Approaches Towards Atropisomerically Stable and Conformationally Pure Diarylamines

Abstract

Diarylamines possess two potentially atropisomeric C-N axes, however there are few examples of atropisomerically stable diarylamines in the literature as the contiguous axes can allow for low energy racemization pathways via concerted bond rotations. Herein we describe highly atropisomerically stable diarylamines that possess barriers to racemization of 30-36 kcal/mol, corresponding to half-lives to racemization on the decade to century time scale at room temperature. Investigation of the factors that led to the high stereochemical stability suggests that increased conjugation of the aniline lone pair of electrons into a more electron deficient aryl ring, coupled with intramolecular hydrogen bonding, locked the corresponding axis into a defined planar conformation, disfavoring the lower energy racemization pathways.

Graphical Abstract

INTRODUCTION

Atropisomerism is a type of axial chirality that arises from differential substitution about a rotationally restricted bond. While chemists have recognized atropisomerism as a key component of natural products^1,2 and chiral catalysts^3–5 for decades, it has also recently become increasingly prevalent in drug discovery, with numerous atropisomers currently in the clinic.^6–10 As bond rotation about the axis can lead to racemization, atropisomers can span the gamut of stereochemical stability, with the classical definition of atropisomerism being conformers that interconvert with a half-life of more than 1000s at a given temperature. LaPlante^11,12 has expanded upon this definition and classified atropisomers based on their barrier to racemization (ΔG_rac) and half-life of racemization at 37 °C: Class-1 (ΔG_rac <20 kcal/mol; t_1/2 <10 s), Class-2 (20 kcal/mol<ΔG_rac<28 kcal/mol; 10 s<t_1/2 >4.5 years), and Class-3 (ΔG_rac>29 kcal/mol; t_1/2 > 4.5 years). It should be noted that Class-1 atropisomers do not meet the classical definition of atropisomerism, but rather exist as non-isolable enantiomeric conformations.

Acyclic diarylamines, which possess two contiguous potentially atropisomeric C-N axes, are one of the most privileged scaffolds in modern drug discovery. Indeed, a search of the Protein Data Bank reveals over 1500 unique diarylamine/protein co-crystal structures, with the C-N axes existing in diverse conformations ranging from planar to orthogonal depending upon the structural attributes of the diarylamine. Many diarylamines, including the FDA approved drugs Bosutinib, Imatinib, and Mefenamic Acid, (Scheme 1A) possess at least one C-N axis that exists in a chiral ‘Class-1 atropisomeric’ conformation when bound to their respective target.

Scheme 1.

Atropisomerism in diarylamines

In these examples of diarylamines, one of the aryl groups (in red) is significantly more electron deficient, resulting in the corresponding C-N axis favoring one of two potential planar conformations, designated here as cis or trans, to maximize conjugation stabilization of the N- lone pair electrons. The second C-N axis, with the more electron rich aryl, can then favor non-planar potentially chiral conformations to minimize torsional strain.

Cis and trans conformations of a diarylamine have vastly different space filling properties with respect to the orientation of the 4 ortho substituents about the diarylamine axes, and can result in conformational diastereomers when the 2^nd axis is in a chiral conformation. As such, cis and trans diarylamine conformations would be expected to have differential biological activities, and the ability to control these conformations would have implications in the design of functional small molecules.

Despite the ubiquity of diarylamines in pharmaceutically relevant scaffolds, their axial chirality has remained less studied than other classes of atropisomer as the two contiguous axes allow for lower energy ‘concerted gearing’ mechanisms of racemization where the planar axis interconverts between cis and trans conformations simultaneously to the 2^nd axis interconverting between atropisomeric conformations. (Scheme 2).¹³

Scheme 2.

Racemization mechanisms of diarylamines

Kawabata was the first to disclose atropisomerically stable diarylamines when his group discovered that diarylamines that possess an intramolecular Hydrogen-bond between an ortho-imine and the diarylamine N-H, as well as one electron poor aryl group,^14,15 existed as ‘near’ Class-3 atropisomers (Scheme 1B). Inspired by Kawabata, we designed N-aryl quinoids that possessed a 5-membered intramolecular N-H-O Hydrogen-bond, finding they could exist as Class-3 atropisomers with ΔG_rac approaching 30 kcal/mol (Scheme 1B).¹⁶ Both Kawabata and our group postulated that the intramolecular Hydrogen-bond disfavored the concerted gearing mechanism by locking the planar axis in a single conformation. More recently, Clayden¹⁷ published a seminal study wherein his group evaluated the amount of steric hindrance needed at each of the four ortho positions of acyclic diarylamines to obtain atropisomerically stable acyclic diarylamines without intramolecular Hydrogen-bonding, obtaining one compound with a ΔG_rac of 31.1 kcal/mol. In this work, Clayden also disclosed a useful linear free energy relationship (LFER) between the barrier to isomerization and the Charton steric parameters (ν) of the four ortho-substituents of the diarylamine C-N axes.

While proving that diarylamines can exist as stable atropisomers, the scaffolds from our lab and Clayden’s work needed at least one quaternary substituent adjacent to the axis to exist as Class-3 atropisomers, while the stereochemical stability of the Kawabata scaffolds proved sensitive to the electronics of the system, requiring 2,4 nitro substitution on the ring whose C-N axis is locked in a planar conformation. Each of these issues limit the use of these scaffolds in medicinal chemical and other functional endeavors. Furthermore, there has been no work on stereochemically stable diarylamines that possess common heterocycles that are seen in the majority of diarylamine containing pharmaceuticals. Herein we report a series of highly atropisomerically stable diarylamines (ΔG_rac up to 36 kcal/mol) based upon pharmaceutically relevant 4-aminoquinoline scaffolds that are isolable in pure cis or trans conformations as determined by intramolecular Hydrogen-bonding.

RESULTS AND DISCUSSION

While Kawabata’s and our previous work postulated that the introduction of intramolecular Hydrogen-bonding can lead to stable diarylamine atropisomers, the Hydrogen-bonding handles were limited to imines or quinoid carbonyls, thus we first set out to evaluate different ortho substitutions that could potentially participate in Hydrogen-bonding with the diarylamine N-H. We initially turned our attention to nitro substitution as in naphthyl based diarylamine 2a, where the Hydrogen-bonding would be expected to preorganize the planar C-N axis into a cis conformation. 2a was synthesized using standard Chan-Lam conditions (Scheme 3) and stereochemically pure samples of each atropisomer were obtained via semi-preparative HPLC using a chiral stationary phase. We observed that 2a had a ΔG_rac of 31.5 kcal/mol when determined at 135 °C in diphenyl ether by observing racemization of an enantiopure sample by HPLC on a chiral stationary phase at set time points (see SI for more details).

Scheme 3.

The synthesis and stereochemical stability of 2a

Conditions: a) 1.0 eq. 1a, 3.0 eq. 1b, 2.0 eq. Cu(OAc)₂, 5.0 eq. Et₃N, 0.1M Dichloroethane.

The observed stereochemical stability of 2a is in line with Clayden’s analysis. While direct application of Clayden’s LFER (ΔG_pred= 60.7*ν_R1+55.8*ν_R2+53.2*ν_R3+26.6*ν_R4-49) to this case is not possible due to the absence of a Charton value for the nitro group in the literature, using an estimated ν for NO₂ of between 0.6 and 0.8 (between the values of Phenyl and methyl ketone) yields a range of predicted ΔG_rac between 31.3kcal/mol and 32.6 kcal/mol that encompasses our experimentally determined stereochemical stability.

We next sought to evaluate the atropisomer stability of analogs of 2a based on the pharmaceutically privileged 4-aminoquinoline scaffold. We were able to expediently obtain compound 2b via a S_NAr based strategy (Scheme 4) and obtained stereochemically pure samples of each atropisomer via semi-preparative HPLC on a chiral stationary phase. Surprisingly, 2b proved to be significantly more stereochemically stable than 2a with a ΔG_rac 34.5 kcal/mol when measured at 148 °C in p-xylenes, corresponding to an estimated t_(1/2) of racemization on the decades timescale at 37 °C.

Scheme 4:

The stereochemical stability of 4-aminoquinolines in ‘cis’ conformation

Conditions: a) 3.0 eq. PhB(OH)₂, 10% Pd(OAc)₂, 20% sPhos, 0.2M 3:1 Toluene: H₂O, 5 eq. K₃PO₄.

Analysis of the small molecule x-ray structure of 2b offered some insights on the ground-state origins of the high stereochemical stability of this system. First, 2b was observed in the intramolecular Hydrogen-bonding containing cis conformation. The structures also revealed that the quinoline C-N bond was shorter (1.35 Å) than what would be expected for the naphthyl C-N bond in naphthyl based diarylamines (~1.41 Å),¹⁷ offering evidence that the increased stereochemical stability of 2b compared to 2a was a result of increased conjugation of the aniline into the quinoline. This increased conjugation would be expected to disfavor conformations where conjugation is broken, such as those needed in the concerted gearing mechanism of racemization, while also amplifying torsional strain at the transition state of racemization due to the shortening of the C-N axis.

We were also able to obtain compounds 2c, where the bromines were replaced with phenyls, and 2d, where the nitro group is replaced with an ester. Each of these compounds existed as Class-3 atropisomers with ΔG_rac determined to be between 32–34 kcal/mol in xylenes. A comparison of the ΔG_rac of 2a and 2c, which possess the same ortho substitutions, (31.5 kcal/mol and 33.0 kcal/mol respectively) suggest that increased conjugation into the quinoline increases the ΔG_rac by ~1.5 kcal/mol versus naphthyl. To probe the role of Hydrogen-bonding in the observed stereochemical stabilities, we determined the ΔG_rac of 2c in different solvents observing increased ΔG_rac in the more polar solvents DMF and ethylene glycol (33.0 kcal/mol in xylenes vs. 33.8 kcal/mol in DMF and 34.2 kcal/mol in ethylene glycol). The increased observed ΔG_rac in the more polar solvents (DMF and ethylene glycol) suggests that increased conjugation into the quinoline ring is the major reason for the observed increase in stereochemical stability, as more polar solvents could be expected to lower barriers that depend largely upon Hydrogen-bonding but raise barriers that depend upon charge separation brought about by delocalization.

Intrigued by these results we next sought to evaluate whether we could render a known pharmaceutically relevant scaffold atropisomerically stable. We settled on the scaffold of bosutinib and neratinib,¹⁸ FDA approved multi-kinase inhibitors with indications for the treatment of Chronic Myeloid Leukemia and HER2 positive breast cancer respectively. Analysis of co-crystal structures of bosutinib (Scheme 1A) bound to its various targets revealed that bosutinib bound them with the quinoline C-N axis in a planar trans conformation, suggesting that we would have to place the prospective Hydrogen-bonding handle at a position peri- relative to the quinoline C-N axis in order to enforce this conformation and to achieve atropisomer stability. This also offered an opportunity to evaluate whether there would be any differences in stereochemical stability between diarylamines in the cis or trans conformations. We were able to synthesize bosutinib analogs with peri substitution using standard quinoline syntheses (see experimental section).

Inspired by recent work from Lectka,¹⁹ wherein his group observed strong Hydrogen-bonding interaction between proximal fluorines and amide NHs, we initially evaluated peri fluorine substituted 2e and were quite surprised when we observed no racemization after prolonged heating at 170 °C in diphenyl ether, meaning that the ΔG_rac was greater than 36 kcal/mol. These stabilities are in line with exemplary high stereochemically stable atropisomers such as BINOL and BINAP.

Intrigued by the high stereochemical stability of 2e, we postulated that we could move away from quaternary substitutions to more pharmaceutically relevant smaller substitutions such as trifluoromethyl or iso-propyl, and still maintain Class-3 atropisomerism. Indeed, ortho-isopropyl substituted 2f and 2g and ortho-trifluoromethyl substituted 2h each existed as Class-3 atropisomers, with ΔG_rac greater than 29 kcal/mol at 90 °C in toluene, a benchmark stability that is considered atropisomerically stable enough for drug development. We also determined ΔG_rac for 2f in the more polar, and potentially hydrogen bonding solvents DMF, and ethylene glycol, observing increases in stability of ~1 kcal/mol in each compared to toluene (29.9 kcal/mol for DMF, and 30.2 kcal/mol for ethylene glycol), suggesting that as with the compounds in scheme 4, increased conjugation into the quinoline is a major driver of the observed increased stereochemical stability. Nonetheless, ¹H NMR offers evidence for the presence of intramolecular Hydrogen-bonding between the diarylamine N-H and the peri-fluorine as we observed strong H-F coupling in the ¹H NMR of each peri-fluoro analog (J values of ~ 27 Hz, See SI), in line with Lectka’s observations in his systems. Analysis of the X-ray structure of 2g further supports intramolecular Hydrogen-bonding as the quinoline C-N axis is observed in the intramolecular Hydrogen-bonding capable trans conformation.

We also evaluated whether other peri substitutions could yield similarly high stereochemical stabilities, finding peri-methoxy substituted bosutinib analog 2i also exists as a Class-3 atropisomer with a ΔG_rac of 29.2 kcal/mol when determined at 90 °C in toluene. An X-ray structure of 2i revealed similar trends to that of 2g, with the quinoline C-N axis being observed in the intramolecular hydrogen-containing trans conformation, with a shortened quinoline C-N axis. On the other hand, analogs that possessed peri substitutions that did not possess the capability for intramolecular Hydrogen-bonding (2j, 2k and 2l) were found to possess significantly lower barriers to interconversion. Compound 2j, which has a peri-methyl, possessed a ΔG_rac of 26.2 kcal/mol when determined in toluene at 55 °C, which is ~3 kcal/mol lower than similar analogs (i.e., 2f, 2i) that possessed a Hydrogen-bonding capable handle in the peri position. Analog 2k which possesses no peri-substitution possessed an even lower ΔG_rac of 24.1 kcal/mol. This offers evidence that intramolecular Hydrogen-bonding has some influence on the observed stereochemical stability of this class of diarylamines, as the larger methyl group would be expected to have a larger steric contribution to the barrier than fluorine or methoxy in the absence of H-bonding.²⁰ It should be noted that there is some precedence in the literature that larger peri substitution can lead to lower barriers to rotation of some bonds²¹ which could explain the lower stability of 2j, however the lower relative stereochemical stability of 2k, as well as the observed H-F coupling by ¹H NMR in the peri-fluoro compounds suggests intramolecular Hydrogen-bonding plays a role in the increased observed stereochemical stabilities of the diarylamines in scheme 5.

Scheme 5.

Study of stereochemical stability of 4-aminoquinolines in ‘trans’ conformation

Finally, compound 2l, which also possesses no peri Hydrogen-bonding handle, but an ortho tert-butyl group possessed a ΔG_rac of ~34.0 kcal/mol, which is at least 2 kcal/mol lower than that of 2e. This observed stereochemical stability is largely in line with what would be expected based on the observed stabilities for the compounds described in scheme 4 (2b-2d), offering evidence that the stereochemical stability of compounds 2b-2d and 2l are largely a result of increased conjugation into the more electron poor quinoline ring with the nitro, ester or nitrile acting as an electron withdrawing group to further increase conjugation into the quinoline ring. While Hydrogen-bonding for compounds 2b-2d contributes little to the observed increase in stereochemical stability, Hydrogen-bonding does appear to enforce the planar C-N axis to be in a cis conformation, at least in the ground state conformations. It should be noted that each of the analogs in scheme 5 that did not possess intramolecular Hydrogen-bonding possessed broad ¹H NMR spectra that are likely due to the presence of tautomers that are not observed with any of the diarylamines that possess intramolecular Hydrogen-bonding.

To further investigate the origins of the observed stereochemical stabilities, we generated conformational energy profiles for the cis to trans interconversion of 2b and 2f (see SI) using the DFT B3LYP/6–31G level of theory. For 2b, the conformational energy profile offered further evidence that the quinoline C-N axis was preorganized into a cis conformation via intramolecular Hydrogen-bonding between one of the nitro oxygens and the diarylamine N-H. The cis conformation of 2b was predicted to be 8.86 kcal/mol lower in energy than the trans conformation which did not possess intramolecular H-bonding, corroborating what we observed in the x-ray structure. The predicted conformational energy profile for 2f reveals a similar trend, with intramolecular Hydrogen-bonding resulting in the trans conformation predicted to be 3.84 kcal/mol lower in energy than the cis conformation that does not possess intramolecular Hydrogen-bonding. Both energy profiles predict large (>30 kcal/mol) energetic barriers to interconversion between cis and trans conformations due to breaking of conjugation between the electron deficient quinoline and the nitrogen lone pair of electrons, offering evidence that the concerted gearing mechanism of racemization is significantly impeded, perhaps explaining the increased observed stereochemical stabilities.

CONCLUSION

In conclusion, this work lays out a strategy to obtain highly atropisomerically stable and conformationally defined diarylamines through the incorporation of increased conjugation into an electron poor heterocyclic scaffold and the introduction of intramolecular Hydrogen-bonding using simple moieties (i.e., F, OMe, NO_2, CO₂R). When these features are employed together, we are able for the first time to obtain diarylamines that exist as Class-3 atropisomers that do not possess an ortho tert-butyl substitution. Our studies suggest that increased conjugation is the major contributor to increased stereochemical stability in these diarylamines, with intramolecular Hydrogen-bonding having minimal effect on the observed ΔG_rac for ortho-substituents, however a somewhat significant effect (>2 kcal/mol) for peri substituents that can partake in Hydrogen-bonding. While the contribution of intramolecular Hydrogen-bonding to the stereochemical stability of these classes of diarylamines may be less than previously postulated, it is notable that Hydrogen-bonding does allow for the design of diarylamines in a defined cis or trans conformation.

This work significantly increases the scope and potential of stereochemically stable diarylamines in the literature. The prevalence of potentially atropisomeric diarylamines in drug discovery should render the findings in this work useful for the design of small molecules with conformations tuned towards a specific target.⁶ Finally this work opens up opportunities in asymmetric catalysis, as diarylamines are novel targets for asymmetric synthesis, and also represent unexplored chiral scaffolds for chiral ligands and catalysts.²²

EXPERIMENTAL SECTION

Materials and General Methods.

¹H and ¹³C NMR spectra were recorded on Varian VNMRS 400 MHz, Varian Inova 500 MHz, spectrometers at 25 °C, unless otherwise noted. All chemical shifts were reported in parts per million (ppm) and were internally referenced to residual protio solvents, unless otherwise noted. Fluorine spectra were referenced to an external TFA standard. Spectral data were reported as follows: chemical shift (multiplicity [singlet (s), doublet (d), triplet (t), quartet (q), pentet (p), and multiplet (m)], coupling constants [Hz], integration). Carbon spectra were recorded with complete proton decoupling. Conventional mass spectra were obtained using Advion ExpressionS CMS (APCI, ASAP). All chemicals used were purchased from Combi Blocks, Sigma Aldrich, TCI, Frontier Scientific, Acros Organics, Strem, Oakwood, Matrix Scientific, Cambridge Isotope Laboratories, or Fisher and were used as received without further purification, unless otherwise noted. All normal phase flash column chromatography (FCC) was performed using Grade 60 Silica Gel (230–400 mesh) purchased from Fisher Scientific. Normal phase flash chromatography was performed on a Biotage Isolera One with Biotage SNAP cartridges (KP Sil 10g-50g) or via manual FCC. Enantioselectivities were recorded using an Agilent 1100 series HPLC using a chiral stationary phase. CHIRALPAK IA, and semipreparative CHIRALPAK IC columns were purchased from Diacel Technologies Corporation. All reactions were heated using oil baths as the heating source unless noted.

Synthesis of N-(5’-(tert-butyl)-[1,1’:3’,1”-terphenyl]-4’-yl)-2-nitronaphthalen-1-amine (2a).

To a 15 mL screw cap glass vial charged with activated 4 Å MS (139 mg) was added (2-nitronaphthalen-1-yl)boronic acid (1a, 50 mg, 0.232 mmol, 1 equiv), 5’-(tert-butyl)-[1,1’:3’,1”-terphenyl]-4’-amine (1b, 210 mg, 0.696 mmol, 3 equiv), copper acetate (83 mg, 0.464 mmol, 2 equiv), triethylamine (0.161 mL, 1.16 mmol, 5 equiv), and 1,2-dichloroethane (2.32 mL, 0.1M). The reaction was allowed to stir at room temperature under ambient air for 48 hours, at which time the reaction mixture was then diluted with ethyl acetate (30 mL) and washed with brine (30 mL), dried over anhydrous sodium sulfate and concentrated in vacuo The obtained residue was purified using flash silica gel column chromatography (gradient up to 5% ethyl acetate in hexanes) to give N-(5’-(tert-butyl)-[1,1’:3’,1”-terphenyl]-4’-yl)-2-nitronaphthalen-1-amine (2a, 64 mg, 58% yield), as an orange solid. ¹H NMR (500 MHz, CDCl₃) δ 11.17 (s, 1H), 7.87 (d, J = 2.2 Hz, 1H), 7.79 (d, J = 9.3 Hz, 1H), 7.70 – 7.63 (m, 2H), 7.53 – 7.43 (m, 4H), 7.39 (dt, J = 15.0, 5.7 Hz, 2H), 7.29 (d, J = 2.1 Hz, 1H), 7.08 – 7.00 (m, 1H), 6.89 (t, J = 7.4 Hz, 1H), 6.81 (dd, J = 8.4, 4.4 Hz, 3H), 6.58 (s, 2H), 1.72 (s, 9H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 145.2, 144.3, 140.5, 139.7, 139.3, 139.1, 137.8, 137.1, 131.1, 129.4, 128.8, 128.4, 128.3, 128.1, 127.5, 127.3, 127.0, 126.5, 125.7, 125.7, 125.1, 124.8, 121.1, 121.0, 118.8, 118.7, 77.2, 36.0, 30.7. HRMS Calculated for C₃₂H₂₉N₂O₂ [M+H]⁺ : 473.2229; Found 473.2246.

Synthesis of N-(2-(tert-butyl)phenyl)-3-nitroquinolin-4-amine (des-Br 2b).

In a 15 mL screw cap glass vial was added 4-chloro-3-nitroquinoline (500 mg, 2.396 mmol, 1 equiv), 2-tert-butyl aniline (0.560 mL, 3.594 mmol, 1.5 equiv), pyridine (0.037 mL, 4.792 mmol, 2 equiv), and 1,2-diethoxyethane (8 mL, 0.3M). The reaction vial was heated at 110 °C for 24 hours. The reaction mixture was extracted in ethyl acetate (30 mL X 3), and the organic layer was washed with brine (30 mL), and dried over anhydrous sodium sulphate. The organic layer was concentrated in vacuo and the obtained residue was purified using flash silica gel column chromatography (gradient up to 10% ethyl acetate in hexanes) to give N-(2-(tert-butyl)phenyl)-3-nitroquinolin-4-amine (des-Br 2b, 558 mg, 72% yield) as a yellow-orange solid. ¹H NMR (400 MHz, CDCl₃) δ 11.13 (s, 1H), 9.48 (s, 1H), 7.98 (d, J = 8.4 Hz, 1H), 7.64 (dd, J = 8.3, 7.0 Hz, 1H), 7.60 (d, J = 8.1 Hz, 1H), 7.40 (d, J = 8.7 Hz, 1H), 7.30 (t, J = 7.5 Hz, 1H), 7.11 (dd, J = 10.9, 4.5 Hz, 2H), 6.87 (d, J = 7.8 Hz, 1H), 1.57 (s, 9H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 150.5, 147.2, 146.9, 144.0, 139.1, 132.3, 130.3, 127.9, 127.6, 127.3, 127.1, 125.3, 118.4, 35.2, 30.4. MS (APCI) Calculated for C₁₉H₂₀N₃O₂ [M+H]⁺ : 322.38; Found 322.41.

Synthesis of N-(2,4-dibromo-6-(tert-butyl)phenyl)-3-nitroquinolin-4-amine (2b).

In a 15 mL screw cap glass vial, was added N-(2-(tert-butyl) phenyl)-3-nitroquinolin-4-amine (des-Br 2b, 800 mg, 2.49 mmol, 1 equiv), and DMF (8.3 mL, 0.3M) followed by N-Bromosuccinimide (930 mg, 5.229 mmol, 2.1 equiv.). The reaction mixture was allowed to stir at room temperature for 12 hours. The reaction mixture was diluted with water (20 mL) and extracted in ethyl acetate (30 X 3 mL). The organic layer was washed with brine (30 mL), and dried over anhydrous sodium sulphate. The organic layer was concentrated in vacuo and the obtained residue was purified using flash silica gel column chromatography (gradient up to 10% ethyl acetate in hexanes) to give N-(2,4-dibromo-6-(tert-butyl)phenyl)-3-nitroquinolin-4-amine (2b, 1.0g, 83% yield), as a yellow solid. ¹H NMR (400 MHz, CDCl₃) δ 11.27 (s, 1H), 9.51 (s, 1H), 8.00 (d, J = 8.4 Hz, 1H), 7.72 (d, J = 2.1 Hz, 1H), 7.70 (dd, J = 7.0, 1.3 Hz, 1H), 7.67 (d, J = 1.8 Hz, 1H), 7.26 – 7.19 (m, 1H), 7.18 – 7.10 (m, 1H), 1.47 (s, 9H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 150.1, 149.9, 147.9, 147.2, 136.2, 134.5, 134.5, 134.4, 132.7, 130.7, 126.1, 125.9, 125.1, 124.9, 122.5, 118.9, 36.5, 30.4. HRMS Calculated for C₁₉H₁₈Br₂N₃O₂ [M+H]⁺ : 477.9766; Found 477.9768.

Synthesis of N-(5’-(tert-butyl)-[1,1’:3’,1”-terphenyl]-4’-yl)-3-nitroquinolin-4-amine (2c).

To a 15 mL screw cap glass vial, was added N-(2,4-dibromo-6-(tert-butyl)phenyl)-3-nitroquinolin-4-amine (2b, 466 mg, 0.977 mmol, 1 equiv), phenylboronic acid (357 mg, 2.93 mmol, 3 equiv), palladium acetate (22mg, 0.0977 mmol, 0.1 equiv), sphos (80 mg, 0.195 mmol, 0.2 equiv), and tripotassium phosphate (1.03g, 4.86 mmol, 5 equiv). The reaction vial was then purged with nitrogen 3 times and toluene (3.25 mL) and water (1.3 mL) were subsequently added. The reaction was heated at 120 °C in an oil bath for 24 hours. The reaction mixture was extracted in ethyl acetate (10 mL X 3) and the organic layers were combined and washed with brine (30 mL) and dried over anhydrous sodium sulphate. The organic layer was concentrated in vacuo and was purified using silica gel column chromatography (gradient up to 10% ethyl acetate in hexanes) to give N-(5’-(tert-butyl)-[1,1’:3’,1”-terphenyl]-4’-yl)-3-nitroquinolin-4-amine (2c, 259.0 mg, 56% yield), as a yellow solid.¹H NMR (500 MHz, CDCl₃) δ 11.21 (s, 1H), 9.10 (s, 1H), 7.90 (d, J = 2.0 Hz, 1H), 7.77 (d, J = 7.9 Hz, 1H), 7.68 (d, J = 7.2 Hz, 2H), 7.58 (t, J = 7.6 Hz, 1H), 7.49 (t, J = 7.6 Hz, 2H), 7.42 – 7.33 (m, 3H), 7.07 (t, J = 7.3 Hz, 1H), 6.96 (t, J = 7.4 Hz, 1H), 6.89 (t, J = 7.6 Hz, 1H), 6.67 (d, J = 6.6 Hz, 2H), 1.67 (s, 9H). ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 149.6, 148.2, 146.5, 146.1, 140.7, 140.7, 140.2, 138.7, 135.9, 132.1, 129.9, 128.9, 128.6, 128.2, 127.9, 127.7, 127.1, 127.1, 126.8, 126.1, 126.0, 125.2, 119.3, 36.0, 30.8. HRMS: Calculated for: C₃₁H₂₈N₃O₂ [M+H]⁺ :474.2182, found : 474.2237

Synthesis of ethyl 4-((2-(tert-butyl)phenyl)amino)quinoline-3-carboxylate (des-Br 2d).

To a mixture of 4-chloro quinoline 3-ethylcoarboxylate (500 mg, 2.12 mmol, 1 equiv.) and 2-tert-butylaniline (477 mg, 3.18 mmol, 1.5 equiv.) in 1,2-diethoxy ethane (10 mL, 0.2M) was added pyridine (781 uL, 9.54 mmol, 4.5 equiv.). The reaction mixture was heated to 100 °C for 12 hours, at which time the reaction mixture was allowed to cool to room temperature and diluted with ethyl acetate (60 mL), washed with brine (30 mL) and dried over anhydrous sodium sulphate. The organic layer was concentrated in vacuo and the obtained residue was purified using flash silica gel column chromatography (gradient up to 60% ethyl acetate in hexanes) to give ethyl 4-((2-(tert-butyl)phenyl)amino)quinoline-3-carboxylate (des-Br 2d, 330 mg, 44% yield), as a yellow solid. ¹H NMR (500 MHz, CDCl₃) δ 10.82 (s, 1H), 9.26 (s, 1H), 7.94 (d, J = 8.2 Hz, 1H), 7.55 (t, J = 8.4 Hz, 2H), 7.34 (d, J = 8.6 Hz, 1H), 7.20 (t, J = 7.5 Hz, 1H), 7.03 (dd, J = 11.7, 7.2 Hz, 2H), 6.82 (d, J = 7.7 Hz, 1H), 4.45 (q, J = 7.1 Hz, 2H), 1.57 (s, 9H), 1.45 (t, J = 7.1 Hz, 3H). ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 169.4, 153.7, 151.6, 151.6, 150.5, 150.4, 137.8, 134.1, 134.1, 134.1, 131.0, 130.2, 130.2, 130.2, 130.0, 125.9, 124.5, 124.1, 121.3, 119.0, 102.6, 61.1, 36.4, 30.4, 14.2. MS (APCI) Calculated for C₂₂H₂₅N₂O₂ [M+H]⁺ : 349.1916; Found 349.1918.

Synthesis of ethyl 4-((2,4-dibromo-6-(tert-butyl)phenyl)amino)quinoline-3-carboxylate (2d).

In a 15 mL screw cap glass vial, was added ethyl 4-((2-(tert-butyl) phenyl) amino) quinoline-3-carboxylate (des-Br 2d, 100 mg, 0.287 mmol, 1 equiv), and DMF (8.3 mL, 0.3M) followed by N-Bromosuccinimide (122 mg, 0.689 mmol, 2.4 equiv). The reaction mixture was allowed to stir at room temperature for 12 hours. The reaction mixture was diluted with water 20 mL and extracted in ethyl acetate (30 mL X 3). The organic layers were combined and washed with brine (30 mL), and dried over anhydrous sodium sulphate. The organic layer was concentrated in vacuo and the obtained residue was purified using flash silica gel column chromatography (gradient up to 60% ethyl acetate in hexanes) to give 4-((2,4-dibromo-6-(tert-butyl)phenyl)amino)quinoline-3-carboxylate (2d, 109 mg, 75% yield), as a yellow solid. ¹H NMR (400 MHz, CDCl₃) δ 11.17 (s, 1H), 9.27 (s, 1H), 7.94 (d, J = 8.0 Hz, 1H), 7.65 (dd, J = 13.3, 2.2 Hz, 2H), 7.61 – 7.55 (m, 1H), 7.11 (d, J = 7.8 Hz, 1H), 7.07 – 7.01 (m, 1H), 4.45 (q, J = 7.1 Hz, 2H), 1.47 (t, J = 7.1 Hz, 3H), 1.44 (s, 9H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 169.4, 153.7, 151.6, 151.6, 150.5, 150.4, 137.8, 134.1, 134.1, 134.1, 131.0, 130.2, 130.2, 130.2, 130.0, 125.9, 124.5, 124.1, 121.3, 119.0, 102.6, 61.1, 36.4, 30.4, 14.2. HRMS Calculated for C₂₂H₂₃Br₂N₂O₂ [M+H]⁺ : 504.0048; Found 504.0050.

Synthesis of 4-((2-(tert-butyl)phenyl)amino)-5-fluoroquinoline-3-carbonitrile (des-Br 2e).

In a 15 mL screw cap glass vial, was added 4-chloro-5-fluoroquinoline-3-carbonitrile (1000 mg, 4.856 mmol, 1 equiv), 2-(tert-butyl) aniline (1.13 mL, 7.28 mmol, 1.5 equiv), pyridine (0.782 mL, 9.708 mmol, 2 equiv), and 1,2-diethoxyethane (16 mL, 0.3M). The reaction vial was then heated at 110 °C for 24 hours. The reaction mixture was extracted in ethyl acetate (30 mL X 3), and the organic layer was washed with brine (30 mL), and dried over anhydrous sodium sulphate. The organic layer was concentrated in vacuo and purified using flash silica gel column chromatography (gradient up to 60% ethyl acetate in hexanes) to give 4-((2-(tert-butyl)phenyl)amino)-5-fluoroquinoline-3-carbonitrile (des-Br 2e, 686 mg, 51% yield) as a yellow-orange solid. ¹H NMR (400 MHz, CDCl₃). δ 8.53 (s, 1H), 8.46 (d, J = 25.9 Hz, 1H), 7.84 (dd, J = 8.5, 0.8 Hz, 1H), 7.69 (td, J = 8.2, 6.1 Hz, 1H), 7.56 (dd, J = 8.0, 1.3 Hz, 1H), 7.43 (td, J = 7.8, 1.7 Hz, 1H), 7.33 (td, J = 7.4, 1.4 Hz, 1H), 7.28 (dd, J = 7.7, 1.6 Hz, 1H), 7.26 – 7.21 (m, 1H), 1.47 (s, 9H). ¹³C{¹H} NMR (101 MHz, CDCl₃). δ 160.9, 158.5, 154.8, 151.6 (d, J = 4.7 Hz), 150.5, 147.3, 136.2, 131.3 (d, J = 11.7 Hz), 129.7, 129.2, 127.7, 127.0, 126.6 (d, J = 3.3 Hz), 115.9, 111.8 (d, J = 24.9 Hz), 108.9 (d, J = 5.9 Hz), 87.2, 35.2, 30.7. ¹⁹F NMR (376 MHz, CDCl₃). δ −113.62 (ddd, J = 25.9, 14.8, 6.0 Hz). MS (APCI) Calculated for C₂₀H₁₉FN₃ [M+H]⁺ : 320.15; Found 320.21.

Synthesis of 4-((2,4-dibromo-6-(tert-butyl)phenyl)amino)-5-fluoroquinoline-3-carbonitrile (2e).

To a stirred solution of 4-((2-(tert-butyl)phenyl)amino)-5-fluoroquinoline-3-carbonitrile (des-Br 2e, 100 mg, 0.313 mmol, 1 equiv.) in DMF (1 mL, 0.3 M) was added N-Bromosuccinimide (134 mg, 0.752 mmol, 2.4 equiv.) at room temperature and the mixture was stirred for 12 hours, at which point it was diluted with ethyl acetate (30 mL) and water (30 mL). The organic layer was washed with brine (15 mL). dried over sodium sulphate, and concentrated in vacuo. The concentrated residue was purified using flash silica gel chromatography (gradient to 60% ethyl acetate in hexanes) to give 4-((2,4-dibromo-6-(tert-butyl)phenyl)amino)-5-fluoroquinoline-3-carbonitrile (2e, 110 mg, 74% yield) as a yellow solid. ¹H NMR (400 MHz, CDCl₃). δ 8.56 (s, 1H), 8.24 (d, J = 26.9 Hz, 1H), 7.87 (d, J = 8.5 Hz, 1H), 7.76 (d, J = 2.0 Hz, 1H), 7.75 – 7.68 (m, 1H), 7.62 (d, J = 2.0 Hz, 1H), 7.28 (dd, J = 14.8, 7.9 Hz, 1H), 1.43 (s, 9H). ¹³C{¹H} NMR (101 MHz, CDCl₃). δ 160.8, 158.3, 154.4, 152.9, 151.0 (d, J = 5.0 Hz), 150.6, 133.4 (d, J = 7.8 Hz), 133.2, 131.4 (d, J = 11.9 Hz), 130.3 (d, J = 7.7 Hz), 127.7, 126.9, 123.9, 115.8, 112.1 (d, J = 24.3 Hz), 108.2 (d, J = 6.1 Hz), 87.5, 36.3, 30.6. ¹⁹F NMR (376 MHz, CDCl₃). δ −112.82 (ddd, J = 26.7, 14.8, 5.9 Hz). HRMS Calculated for C₂₀H₁₇Br₂FN₃ [M+H]⁺ : 475.9773; Found 475.9774.

Synthesis of 2-cyano-N-(2,4-dibromo-6-isopropyl-3-methoxyphenyl) acetamide (1f).

To a stirred solution of 2-cyanoacetic acid (323 mg, 3.84 mmol, 2 equiv) in DMF (19 ml, 0.1M) was added EDC.HCl (323 mg, 3.84 mmol, 2 equiv.) followed by DIPEA (1.3 mL, 7.6 mmol, 4 equiv.) and 2,4-dibromo-6-isopropyl-3-methoxyaniline at room temperature. The reaction mixture was heated at 60 °C for 6 hours. The reaction mixture was then diluted with ethyl acetate (30 mL) and washed with water (30 mL X 3) and brine (30 mL). The organic layer was dried over anhydrous sodium sulphate, concentrated in vacuo, and purified using flash silica gel chromatography (gradient up to 50% ethyl acetate in hexanes) to give 2-cyano-N-(2,4-dibromo-6-isopropyl-3-methoxyphenyl) acetamide (1f, 630 mg, 86% yield). ¹H NMR (400 MHz, DMSO-d6): δ 10.06 (s, 1H), 7.61 (s, 1H), 3.95 (s, 2H), 3.78 (s, 3H), 3.09 – 2.92 (m, 1H), 1.12 (d, J = 6.9 Hz, 6H). ¹³C{¹H} NMR (101 MHz, DMSO-d6): δ 161.7, 151.9, 145.6, 134.1, 129.3, 129.3, 119.9, 116.7, 115.7, 60.2, 39.5, 28.6, 25.4. MS (APCI): Calculated for C₁₃H₁₄Br₂N₂O₂ [M+H]⁺: 388.9; Found: 388.9 m/z.

Synthesis of 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-5-fluoroquinoline-3-carbonitrile (2f).

To a mixture of 3-fluoroaniline (31 mg, 0.21 mmol, 1.1 equiv.) and alpha-cyanoamide 1f (100 mg, 0.25 mmol, 1 equiv.) was added triethyl orthoformate (1.25 mL) in isopropanol (2 mL, 0.1 M) at room temperature. The reaction mixture was heated at 130 °C for 12 hours. After cooling down the reaction mixture, it was charged with water (2 mL) and heated to 130 °C for 10 min. The reaction mixture was then cooled down to room temperature and diluted with ethyl acetate (10 mL). The organic layer was collected and washed with water (30 mL X 3), brine (30 mL) and dried over sodium sulphate. The residue was purified using flash silica gel chromatography (gradient to 20% ethyl acetate in hexanes) to give 125 mg of a sticky oil that was dissolved in n-butyronitrile (2.1 mL 0.1 M), charged with POCl₃ (5 equiv.) and heated to 110 °C for 12 hours. After cooling down to room temperature, sat. NaHCO₃ (10 mL) was added and the mixture let stir for 10 min. The reaction mixture was diluted with ethyl acetate (30 mL) and the organic layer was washed with water (30 mL X 3), brine (30 mL) and dried over anhydrous sodium sulphate. The concentrated residue was purified using flash silica gel chromatography (gradient to 60% ethyl acetate in hexanes) to give of 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-5-fluoroquinoline-3-carbonitrile (2f, 75 mg, 60% yield) as a yellow solid.¹H NMR (400 MHz, CDCl₃) δ 8.54 (s, 1H), 8.18 (d, J = 26.0 Hz, 1H), 7.87 (d, J = 8.4 Hz, 1H), 7.72 (td, J = 8.2, 6.1 Hz, 1H), 7.55 (s, 1H), 7.28 (ddd, J = 14.7, 7.9, 1.1 Hz, 2H), 3.92 (s, 3H), 3.25 – 3.07 (m, 1H), 1.26 (d, J = 6.9 Hz, 3H), 1.23 (d, J = 6.9 Hz, 3H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 160.88, 158.39, 154.46, 152.97, 150.85 (d, J = 5.1 Hz), 150.6, 146.5, 133.2, 131.5 (d, J = 14.0 Hz), 129.9, 129.9, 126.8, 122.0, 119.8, 115.6, 112.2 (d, J = 25.0 Hz), 108.2 (d, J = 6.1 Hz), 107.9, 86.8, 60.5, 29.6, 23.8, 22.4. ¹⁹F NMR (376 MHz, CDCl₃) δ −112.51 (ddd, J = 26.1, 14.7, 6.1 Hz).HRMS Calculated for C₂₂H₂₁Br₂FN₃O₃ [M+H]⁺ : 491.9722; Found 491.9733.

Synthesis of 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-5-fluoro-6,7-dimethoxyquinoline-3-carbonitrile (2g).

To a mixture of 3-fluoro-4,5-dimethoxy aniline (177 mg, 0.84 mmol, 1.1 equiv.) and alpha-cyanoamide 1f (300 mg, 0.769 mmol, 1 equiv.) was added triethyl orthoformate (2 mL) in isopropanol (8.4 mL, 0.1 M) at room temperature. The reaction mixture was heated at 130 °C for 12 hours. After cooling to room temperature water (2 mL) was added and the mixture was heated to 130 °C for 10 min. The reaction mixture was then cooled down to room temperature and diluted with ethyl acetate (30 mL). The organic layer was collected and was washed with water (30 mL X 3), brine (30 mL) and dried over anhydrous sodium sulphate. The concentrated residue was purified using flash silica gel chromatography (gradient up to 20% ethyl acetate in hexanes) to give 400 mg of a sticky oil that was diluted in n-butyronitrile (8.4 mL, 0.1 M). POCl₃ (5 equiv.) was added and the reaction mixture was stirred in oil bath at 110 °C for 12 hours. After cooling down to room temperature, sat. NaHCO₃ (10 mL) was added and the mixture let stir for 10 min. The reaction mixture was diluted with ethyl acetate (30 mL) and the organic layer was collected and washed with water (30 mL X 3), brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The concentrated residue was purified using flash silica gel chromatography (gradient to 60% ethyl acetate in hexanes) to give 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-5-fluoro-6,7-dimethoxyquinoline-3-carbonitrile (2g, 242 mg, 63% yield) as a yellow solid. ¹H NMR (400 MHz, CDCl₃): δ 8.42 (s, 1H), 7.95 (d, J = 24.6 Hz, 1H), 7.54 (s, 1H), 7.26 (s, 1H), 4.05 (s, 3H), 4.04 (s, 3H), 3.91 (s, 3H), 3.22 – 3.06 (m, 1H), 1.26 (d, J = 6.9 Hz, 3H), 1.22 (d, J = 6.9 Hz, 3H). ¹³C{¹H} NMR (101 MHz, CDCl₃): δ 156.7 (d, J = 7.6 Hz), 156.7, 153.8, 153.7, 152.9, 151., 150.2, 150.2 (d, J = 4.8 Hz), 146.6, 146.4 (d, J = 2.1 Hz), 146.4, 136.6, 136.5, 133.5, 129.9, 122.1, 119.6, 115.8, 106.1, 103.1, 85.7, 77.2, 62.1, 60.4, 60.4, 56.5, 29.5, 23.8, 22.4. ¹⁹F NMR (376 MHz, CDCl₃): δ −134.03 (d, J = 24.7 Hz). HRMS Calculated for C₂₀H₁₇Br₂FN₃ [M+H]⁺ : 551.9934; Found 551.9945.

Synthesis of 5-fluoro-4-((5-methoxy-2(trifluoromethyl)phenyl)amino)quinoline-3-carbonitrile (des-Br 2h):

In a 15 mL screw cap glass vial was added 4-chloro-5-fluoroquinoline-3-carbonitrile (1000 mg, 4.85 mmol, 1 equiv), 5-methoxy-2-(trifluoromethyl) aniline (1390 mg, 7.28 mmol, 1.5 equiv), pyridine (0.782 mL, 9.708 mmol, 2 equiv), and 1,2-diethoxyethane (16 mL, 0.3M). The reaction vial was then heated at 110 °C for 24 hours. The reaction mixture was diluted with water and extracted with ethyl acetate (30 mL X 3). The organic layers were combined and washed with brine (30 mL), dried over anhydrous sodium sulfate, and concentrated in vacuo. The obtained residue was purified using flash silica gel column chromatography (gradient up to 60% ethylacetate in hexanes) to give 5-fluoro-4-((5-methoxy-2(trifluoromethyl)phenyl)amino)quinoline-3-carbonitrile (des-Br 2h, 1104 mg, 63% yield) as a yellow-orange solid. ¹H NMR (400 MHz, CDCl₃) δ 8.59 (s, 1H), 8.39 (d, J = 24.5 Hz, 1H), 7.86 (dd, J = 8.4, 0.7 Hz, 1H), 7.75 – 7.66 (m, 2H), 7.32 – 7.21 (m, 1H), 7.01 – 6.93 (m, 2H), 3.86 (s, 3H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 162.7, 160.6, 158.1, 154.0, 150.6 (d, J = 4.5 Hz), 150.5, 136.9, 131.6 (d, J = 9.3 Hz), 128.6 – 128.3 (m), 126.6 (d, J = 2.1 Hz), 123.8 (d, J = 271.8 Hz), 119.3 (q, J = 30.5 Hz), 115.6, 113.4 (d, J = 115.3 Hz), 112.2 (d, J = 24.5 Hz), 109.2 (d, J = 6.3 Hz), 88.7, 55.7 (q, J = 8.1 Hz). ¹⁹F NMR (376 MHz, CDCl₃) δ −60.45 (s), −112.21 – −114.55 (m). MS (APCI) Calculated for C₂₀H₁₉FN₃ [M+H]⁺ : 361.08; Found 362.10.

Synthesis of 4-((2,4-dibromo-3-methoxy-6-(trifluoromethyl)phenyl)amino)-5-fluoroquinoline-3-carbonitrile (2h).

To a stirred solution of 4-((2-(trifluoro)phenyl)amino)-5-fluoroquinoline-3-carbonitrile (100 mg, 0.277 mmol, 1 equiv.) in DMF (1 mL, 0.3 M) was added N-Bromosuccinimide (118 mg, 0.66 mmol, 2.4 equiv.) at room temperature and reaction mixture was stirred for 12 hours. The reaction mixture was diluted with ethyl acetate (30 mL) and water (30 mL). The organic layer was collected and washed with brine (15 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The resultant residue was purified using flash silica gel chromatography (gradient up to 60% ethyl acetate in hexanes) to give 4-((2,4-dibromo-3-methoxy-6-(trifluoromethyl)phenyl)amino)-5-fluoroquinoline-3-carbonitrile (2h, 102 mg, 71% yield) as a yellow solid. ¹H NMR (400 MHz, CDCl3). δ 8.58 (s, 1H), 8.36 (d, J = 26.3 Hz, 1H), 7.97 (s, 1H), 7.90 (d, J = 8.1 Hz, 1H), 7.75 (td, J = 8.2, 6.1 Hz, 1H), 7.30 (ddd, J = 14.6, 7.9, 1.0 Hz, 1H), 3.99 (s, 3H). ¹³C{¹H} NMR (101 MHz, CDCl3). δ 160.6, 158.2, (d, J = 16.7 Hz), 153.7, 150.4, 149.9 (d, J = 4.9 Hz), 134.2, 131.8 (d, J = 12.1 Hz), 130.4 (dd, J = 5.2, 2.5 Hz), 127.8, 126.8, 124.3, 123.4, 120.7, 119.1, 115.5, 112.5 (d, J = 24.5 Hz), 108.3 (d, J = 6.2 Hz), 87.7, 77.2, 60.6, 29.6, 14.1. HRMS Calculated for C₁₈H₁₀B_r2F₃N₃O [M+H]+ : 517.9127; Found 517.9123.

Synthesis of 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-5-methoxyquinoline-3-carbonitrile (2i).

To a mixture of m-anisidine (94 mg, 0.84 mmol, 1.1 equiv.) and alpha-cyanoamide 1f (300 mg, 0.77 mmol, 1 equiv.) was added triethyl orthoformate (3.5 mL) in isopropanol (7.7 mL, 0.1 M) at room temperature and reaction mixture was heated at 130 °C for 12 hours. After cooling to room temperature, water (5 mL) was added and the mixture was heated at 130 °C for 10 minutes. The reaction mixture was then cooled to room temperature and diluted with ethyl acetate (60 mL) and washed with water (30 mL X 3) followed by brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The resultant residue was purified using flash silica gel chromatography (gradient up to 20% ethyl acetate in hexanes) to give 310 mg of a sticky oil which was dissolved in n-butyronitrile (7.7 mL, 0.1 M). POCl₃ (5 equiv.) was added and the mixture was stirred at 110 °C for 12 hours. After cooling down to room temperature sat. NaHCO₃ (10 mL) was added and mixture stirred for 10 min. The reaction mixture was diluted with ethyl acetate (30 mL) and washed with water (30 mL X 3) followed by brine (30 mL) and dried over anhydrous sodium sulphate. The concentrated residue was purified using flash silica gel chromatography (gradient up to 60% ethyl acetate in hexanes) to give 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-5-methoxyquinoline-3-carbonitrile (2i, 182 mg, 61% yield) as a yellow solid. ¹H NMR (400 MHz, CDCl₃) δ 9.86 (s, 1H), 8.47 (s, 1H), 7.73 – 7.61 (m, 2H), 7.53 (s, 1H), 6.99 (d, J = 7.6 Hz, 1H), 4.11 (s, 2H), 3.92 (s, 2H), 3.14 (tt, J = 12.6, 6.2 Hz, 1H), 1.27 (d, J = 6.9 Hz, 5H), 1.21 (d, J = 6.8 Hz, 3H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 157.5, 154.3, 153.1, 152.9, 151.0, 146.3, 134.2, 131.6, 131.5, 129.8, 129.7, 123.4, 121.9, 119.1, 116.4, 106.7, 60.6, 57.0, 29.7, 23.9, 22.3. HRMS Calculated for C₂₁H₂₀Br₂N₃O₂ [M+H]⁺ : 503.9922; Found 503.9919.

Synthesis of 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-5,7-dimethylquinoline-3-carbonitrile (2j).

To a mixture of 3,5-dimethyl aniline (51 mg, 0.423 mmol, 1.1 equiv.) and alpha-cyanoamide 1f (150 mg, 0.37mmol, 1 equiv.) was added of triethyl orthoformate (1.5 mL) in isopropanol (3.7 mL, 0.1 M) at room temperature and the mixture was heated at 130 °C for 12 hours. After cooling to room temperature, water (2 mL) was added and the reaction mixture was heated at 130 °C for 10 minutes. The reaction mixture was cooled to room temperature and diluted with ethyl acetate (30 mL) and washed with water (30 mL X 3), brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The concentrated residue was purified using flash silica gel chromatography (gradient up to 20% ethyl acetate in hexanes) to give 100 mg of a sticky oil which was dissolved in n-butyronitrile (3.7 mL, 0.1 M). POCl₃ (5 equiv.) was added and the reaction mixture was heated at 110 °C for 12 hours. After cooling to room temperature, sat. NaHCO₃ (10 mL) was added and the mixture stirred for 10 min. The reaction mixture was then diluted with ethyl acetate (30 mL) and washed with water (30 mL X 3), brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The concentrated residue was purified using flash silica gel chromatography (gradient up to 60% ethyl acetate in hexanes) to give 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-5,7-dimethylquinoline-3-carbonitrile (2j, 97 mg, 83% yield) as a yellow solid. ¹H NMR (500 MHz, CDCl₃) δ 8.46 (s, 1H), 7.68 (s, 1H), 7.52 (s, 1H), 7.37 (s, 1H), 7.19 (s, 1H), 3.91 (s, 3H), 3.07 (s, 3H), 2.49 (s, 3H), 1.25 (d, J = 6.8 Hz, 3H), 1.20 (d, J = 6.8 Hz, 3H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 153.0, 152.9, 152.9, 152.8, 141.9, 133.0, 132.9, 130.0, 129.8, 129.7, 128.6, 119.0, 116.2, 87.2, 60.5, 29.5, 25.5, 24.2, 22.2, 21.3, 21.2. HRMS Calculated for C₂₂H₂₂Br₂N₃O [M+H]⁺ : 502.0130; Found 502.0139.

Synthesis of 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-6,7-dimethoxyquinoline-3-carbonitrile (2k).

To a mixture of 3,4-dimethoxyaaniline (120 mg 0.423 mmol, 1.1 equiv.) and alpha-cyanoamide 1f (300 mg. 0.769 mmol, 1 equiv.) was added triethyl orthoformate (4 mL) in isopropanol (4.2 mL, 0.1 M) at room temperature and the reaction mixture was heated at 130 °C for 12 hours. After cooling to room temperature water (2 mL) was added and the mixture was heated at 130 °C for 10 minutes. The reaction mixture was then cooled to room temperature, diluted with ethyl acetate (30 mL), washed with water (30 mL X 3), brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The resultant residue was purified using flash silica gel chromatography (gradient up to 20% ethyl acetate in hexanes) to give 400 mg of a sticky oil which was dissolved in n-butyronitrile (0.1 M). POCl₃ (5 equiv.) was added and the reaction mixture was stirred at 110 °C for 12 hours. After cooling to room temperature sat. NaHCO₃ (10 mL) was added and the mixture stirred for 10 min. The reaction mixture was diluted with ethyl acetate (30 mL), washed with water (30 mL X 3), brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The residue was purified using flash silica gel chromatography (gradient up to 60% ethyl acetate in hexanes to give 4-((2,4-dibromo-6-isopropyl-3-methoxyphenyl)amino)-6,7-dimethoxyquinoline-3-carbonitrile (2k, 297 mg, 77% yield) as a yellow solid. ¹H NMR (400 MHz, CDCl₃) δ 8.47 (s, 1H), 7.52 (s, 1H), 7.34 (s, 1H), 7.26 (br s, 1H), 7.03 (s, 1H), 3.98 (s, 3H), 3.87 (s, 3H), 3.76 (s, 3H), 3.22 – 3.03 (m, 1H), 1.19 (d, J = 6.9 Hz, 3H), 1.12 (d, J = 6.9 Hz, 3H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 153.8, 152.9, 150.8, 149.7, 149.6, 146.4, 146.2, 134.8, 130.0, 129.9, 121.7, 118.7, 116.4, 111.9, 109.2, 99.7, 87.1, 60.5, 60.4, 56.2, 56.2, 55.9, 55.8, 29.2, 23.4, 22.9. HRMS Calculated for C₂₂H₂₂Br₂N₃O₃ [M+H]⁺ : 534.0028; Found 534.0038.

Synthesis of N-(2-(tert-butyl)phenyl)-2-cyanoacetamide (1l).

To a stirred solution of 2-cyanoacetic acid (390 mg, 4.0 mmol, 2 equiv.) in DMF (10 mL), was added EDC.HCl (390 mg, 2.0 mmol, 2 equiv.), 2-tert-butyl aniline (300 mg, 2.0 mmol, 1 equiv.) and DIPEA (1.3 mL, 7.6 mmol, 4 equiv.). The reaction mixture was heated at 80 °C for 16h, upon which time the mixture was diluted with water (30 mL) and extracted with ethyl acetate (30 mL). The organic layer was collected and washed with water (30 mL X 3), brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The resultant residue was purified using flash silica gel chromatography (gradient up to 80% ethyl acetate in hexanes) to give N-(2-(tert-butyl)phenyl)-2-cyanoacetamide (1l, 250 mg, 57 % yield). ¹H NMR (599 MHz, CDCl₃) δ 8.10 (br s, 1H), 7.41 (d, J = 7.8 Hz, 1H), 7.30 (t, J = 8.7 Hz, 1H), 7.22 (t, J = 7.0 Hz, 1H), 7.18 (d, J = 7.4 Hz, 1H), 3.48 (s, 2H), 1.36 (s, 9H). ¹³C{¹H} NMR (151 MHz, CDCl₃) (1:1.5 rotameric mixture) δ 160.4, 160.3, 144.4, 144.3, 133.7, 133.6, 128.8, 128.7, 127.6, 127.6, 127.0, 126.9, 114.7, 34.6, 34.6, 30.6, 30.5, 26.3, 26.3. HRMS Calculated for C₁₃H₁₆N₂O [M+H]⁺: 217.1263; Found: 217.1337 m/z.

Synthesis of 4-((2-(tert-butyl)phenyl)amino)quinoline-3-carbonitrile (des-Br 2l).

To a mixture of aniline (100 mg, 0.423 mmol, 1.1 equiv.) and alpha-cyanoamide 1l (300 mg, 0.38 mmol, 1 equiv.) was added triethyl orthoformate (6 mL) in isopropanol (4.2 mL, 0.1 M) at room temperature. The reaction mixture was heated at 130 °C for 12 hours. After cooling to room temperature, water (2 mL) was added and the reaction was heated at 130 °C for 10 min. The reaction mixture was cooled to room temperature and diluted with ethyl acetate (30 mL) and washed with water (30 mL X 3), brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The resultant residue was purified using flash silica gel chromatography (gradient up to 20% ethyl acetate in hexanes) to give 400 mg of a sticky oil which was diluted in n-butyronitrile (4.2 mL, 0.1 M). POCl₃ (5 equiv.) was added and the reaction mixture was stirred in heating oil bath at 110 °C for 12 hours. After cooling down the reaction mixture to room temperature sat. NaHCO₃ (10 mL) was added and the mixture was stirred for 10 min. The reaction mixture was diluted with ethyl acetate (30 mL) and the organic layer was collected and washed with water (30 mL X 3), brine (30 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The resultant residue was purified using flash silica gel chromatography (gradient up to 60% ethyl acetate in hexanes) to give 4-((2-(tert-butyl)phenyl)amino)quinoline-3-carbonitrile (des-Br 2l, 310 mg, 69% yield) as a yellow solid. ¹H NMR (400 MHz, CDCl₃) δ 8.65 (s, 1H), 8.05 (d, J = 7.6 Hz, 1H), 7.76 (ddd, J = 14.6, 7.9, 4.5 Hz, 2H), 7.57 (dd, J = 8.0, 1.5 Hz, 1H), 7.48 (ddd, J = 8.4, 6.9, 1.2 Hz, 1H), 7.41 – 7.34 (m, 1H), 7.25 (td, J = 7.6, 1.5 Hz, 2H), 7.14 (dd, J = 7.9, 1.2 Hz, 2H), 1.49 (s, 9H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 152.6, 151.6, 149.3, 146.2, 137.5, 131.7, 130.6, 128.9, 128.5, 127.7, 127.2, 126.5, 121.3, 117.9, 116.5, 88.6, 35.3, 30.7. HRMS Calculated for C₂₀H₂₀N₃ [M+H]⁺ : 302.1654; Found 302.1579.

Synthesis of 4-((2,4-dibromo-6-(tert-butyl)phenyl)amino)quinoline-3-carbonitrile (2l).

To a stirred solution of 4-((2-(tert-butyl)phenyl)amino)quinoline-3-carbonitrile (des-Br 2l, 130 mg, 0.313 mmol, 1 equiv.) in DMF (1 mL, 0.3 M) was added N-Bromosucicnimide (185 mg, 0.752 mmol, 2.4 equiv.). The reaction mixture was stirred for 12 hours at room temperature upon which time it was diluted with ethyl acetate (30 mL) and water (30 mL). The organic layer was collected and washed with brine (15 mL), dried over sodium sulfate and concentrate in vacuo. The resultant residue was purified using flash silica gel chromatography (gradient up to 60% ethyl acetate in hexanes) to give 4-((2,4-dibromo-6-(tert-butyl)phenyl)amino)quinoline-3-carbonitrile (2l, 153 mg, 77% yield) as a yellow solid. ¹H NMR (400 MHz, CDCl₃) δ 8.59 (s, 1H), 8.05 (s, 1H), 7.93 (s, 1H), 7.80 (t, J = 7.6 Hz, 1H), 7.73 (s, 1H), 7.66 – 7.54 (m, 2H), 7.15 (s, 1H), 1.41 (s, 9H). ¹³C{¹H} NMR (101 MHz, CDCl₃) δ 152.9, 150.8, 148.8, 133.5, 131.9, 130.7, 130.4, 128.0, 127.0, 123.8, 120.0, 117.4, 116.2, 87.2, 36.4, 30.7. HRMS Calculated for C₂₀H₁₈Br₂N₃ [M+H]⁺ : 457.9867; Found 457.9868.