Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2017 Jul 1.
Published in final edited form as: J Heterocycl Chem. 2015 Jun 4;53(4):1065–1073. doi: 10.1002/jhet.2372

Synthesis and chemical reactivity of a 6-Me-3,2-hydroxypyridinone dithiazolide with primary amines: a route to new hexadentate chelators for hard metal(III) ions

Sylvie L Pailloux a, Sean Nguyen a, Stephanie Zhou a, Marisa E Hom a, Michelle N Keyser a, Danil Smiles a, Kenneth N Raymond a
PMCID: PMC5029124  NIHMSID: NIHMS699195  PMID: 27667855

Abstract

A hydroxypyridinone building block, bifunctionalized with thiazoline, has been prepared from orthogonally protected 2-(3-(benzyloxy)-4-(ethoxycarbonyl)-6-methyl-2-oxopyridin-1(2H)-yl) acetic acid. The reactivity of the dithiazolide has been explored with two primary amines, leading to the synthesis and characterization of four new hexadentate ligands. Their complexes with selected hard trivalent ions pertinent to potential molecular imaging applications have been surveyed.

Graphical Abstract

graphic file with name nihms699195u1.jpg

INTRODUCTION

Hydroxypyridinones (HOPOs) have been developed for the last 20 years as chelators for hard metal ions [1]. The HOPO 6 membered ring has three major isomers [1]: 3,4-HOPO, 3,2-HOPO, and 1,2-HOPO, as depicted in Figure 1. Some HOPOs have been used in pharmaceutical applications, since their affinity for iron makes them good candidates for treating metal overload, protozoic and bacterial infections, as well as neurodegeneration [2]. HOPOs also have been employed as MMP inhibitors as well as for antidiabetic and anticancer treatments when coordinated to d-block elements such as Zn, Mo, V, Ru and Os [3]. Additionally, HOPOs with Gd and Ga have been utilized as imaging probes and as decorporation agents of actinides [4]. Lastly, several studies of luminescence performance of 1,2-HOPO complexes with europium have been published and they display good quantum yields [5,6].

Figure 1.

Figure 1

Open in a new tab

Examples of the hydroxypyridinone family.

We have developed powerful MRI contrast agents involving 1,2-HOPO and 1-Me-3,2-HOPO which have been connected with a tripodal primary amine (TREN, TACN, Mesyl) to form hexadentate ligands that strongly complex Gd(III) [7,8,9]. These complexes have two or three sites available for water coordination (q), improving the relaxivity of the complex by a factor of 2 or 3 in comparison to all other contrast agents currently on the market, which have a q=1. To allow the incorporation of solubilizing moieties (dendrimers) or the conjugation to nano-supports (MS2, Ester Amine (EA) dendrimer), one HOPO moiety has been replaced by a terephthalamide (TAM) that has two amides built into the motif [10,11,12]. However, the thermodynamic stability of the Gd complexes is lowered when more than one HOPO unit is substituted by a TAM moiety [13, 14].

To mitigate the thermodynamic stability problem, a new hydroxypyridinone (6-Me-3,2-HOPO) has been developed and is described herein. This scaffold enables functionalization of the 1-N position, allowing for structural adjustment and the formation of neutral complexes with M(III) metal ions. This chemistry also supports the formation of a cage environment, which increases the kinetic stability of the complex [1,4]. With the exception of work by Gopalan [15], Rapoport [16] and Van der Eycken [17] very little work has been reported on 3,2-HOPOs that enables reactivity at the 1-N position or leads to the development of new HOPO systems. We describe herein a scalable synthesis for a new HOPO derivative bi-functionalized at positions 1 and 4 with thiazolide rings. Facile reaction of this reagent with primary amines enables for the synthesis of tripodal and bi-macrocyclic cage ligands that are capable of hexadentate coordination with hard metal ions such as Gd(III) and Ga(III).

RESULTS AND DISCUSSION

The formation of the HOPO ring 3 (Scheme 1) followed a procedure described by Feist [18]. However yields obtained were typically lower by 20 – 30%. The 1H NMR spectrum was consistent with previously described results [13, 18], and the 13C NMR spectrum showed a characteristic peak at δ (ppm) 102.18 for the only carbon in the ring carrying a proton [13]. A single X-ray diffraction determination of 3 has been previously described [13].

Scheme 1.

Scheme 1

Open in a new tab

Synthesis of bifunctionalized 6-methyl-3,2-HOPOs, 5 and 6.

The reaction of HOPO 3 with tert-butyl iodoacetate presents a possible competition between N-alkylation and O-alkylation. This was previously addressed by us through the use of cetylpyridinium for phase transfer that favors the O-alkylation [13]. In a second approach, we studied the use of strong bases such as 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) which favors O- over N-alkylation in a homogeneous mixture [19, 20]. By using this approach we succeeded in synthesizing 6-Me-3,2-HOPO(Bn) 4 with better yield and reproducibility as well as a simpler purification. 1H and 13C NMR spectra for 4 were consistent with previously described spectra [13]. Specifically, the 13C NMR spectrum contains a diagnostic methylene carbon δ (ppm) 74.04. The molecular structure of 4 was unequivocally confirmed by single crystal X-ray diffraction structure determination. Compound 5 results from N-alkylation of the enolate of an amide (Scheme 1). We first envisaged the synthesis of the diester 5 using potassium on alumina [13]. In this case the tert-butyl ester 5 was obtained with moderate yield. Alternatively, by using potassium carbonate in DMF, the O-alkylated 5a was also obtained (Scheme 2).

Scheme 2.

Scheme 2

Open in a new tab

O-alkylation of the enolate form of 6-Me-3,2-HOPO 4.

In comparison with 5, 5a is considered to be more thermodynamically stable due to higher aromaticity. The 1H NMR spectra of thermodynamic 5a and kinetic 5 compounds are presented in Figure 2. The methylene resonance for the O-alkylated compound 5a shows a more aromatic shift (δ = 6.96 ppm) than the N-alkylated compound 5 (δ = 6.19 ppm). In addition the molecular structure 5 was confirmed by single X-ray crystallography diffraction methods.

Figure 2.

Figure 2

Open in a new tab

1H NMR comparison between resulting products of competitive N- 5, (bottom) vs O-alkylation 5a (top)

Functional similarity between hydroxypyridinone and quinolinone systems suggested the development of a one-step selective N-alkylation over O-alkylation of compound 4 through the use of magnesium tert-butoxide [21]. In the present system, it is expected that the Mg(II) ion coordinates with the carbonyl O-atom of the cyclic amide to form a five-membered ring intermediate (Scheme 3) that favors N-alkylation, producing compound 6 with 80% yield [21]. It is noted that the acid 6 was first obtained by acid hydrolysis of the tert-butyl ester 5 with high yield (Scheme 1).

Scheme 3.

Scheme 3

Open in a new tab

Possible mechanism of N-Alkylation of 6-Me-3,2-HOPO 4.

The amide bond formation was first attempted by generating the N-hydroxysuccinimide (NHS) active ester intermediate, 6a (Scheme 4). Compound 10c, was obtained with moderate yield. Saponification of the ester function of 10c was obtained, but the activation of position 4 in active ester NHS or thiazolide failed. Benzyl group of compound 10c was removed in acidic condition and permitted the synthesis of the Gd complex 12c in the following step.

Scheme 4.

Scheme 4

Open in a new tab

Reactivity of functionalized 6-Me-3,2-HOPO.

To access a cage structure or more soluble structures, the di-thiazolide intermediate 8 was developed (Scheme 4).

Following saponification of 6, the di-acid 7 was combined with TBTU and 2-mercaptothiazolide to give 8 with a good overall yield. Compound 8 displays four characteristic triplets in its 1H NMR spectrum at 4.62, 4.31, 3.42 and 2.88 ppm. These peaks correspond to the four methylene groups present in the two thiazolides fragments.

Primary amines tert-butyl-(2-aminoethyl)carbamate and TREN regioselectively reacted with the thiazolide (on the N side) of 8 with formation of 9 and 9a respectively (Scheme 5). The 1H NMR spectra of 9 and 9a show two methylene signals δ (ppm) 4.32 and 2.89 (9) and 4.30 and 2.98 (9a) corresponding to the resonance of the thiazolide left in position 4 of the ring. The mono-thiazolide of 9 and 9a reacts further with the primary aliphatic amines of TREN and tert-butyl (2-aminoethyl)carbamate respectively to form 10 and 10a. The methylene protons of TREN were observed at δ (ppm) 3.01 and 2.24 for 10 and δ (ppm) 3.19 and 2.53 for 10a in their respective 1H NMR spectra. The macrocyclic cage 10b was obtained by reaction of one equivalent of TREN with one equivalent of 9a using high dilution conditions. In all cases the deprotections of BOC and benzyl groups were achieved by treatment with acid.

Scheme 5.

Scheme 5

Open in a new tab

Synthesis of hexadentate HOPO based ligands 11-11b.

The coordination chemistry of the new hexadentate ligand was surveyed with hard, trivalent cations. In particular, one equivalent of each of the deprotected ligands 11-11b (Scheme 5) and 11c (Scheme 4) was combined with one equivalent of gadolinium chloride hexahydrate (GdCl3·6H2O) at reflux in methanol (MeOH) and in the presence of pyridine. The resulting Gd complex 12-12c was characterized by microanalysis and by mass spectrometry, and the latter showed the expected isotopic distributions and mass/charge values. In general, the coordination of the deprotected ligand 11-11c to the M(III) ions results in broadening of the peaks in the IR spectra compared to the free ligands. In the cases of the Gd complexes with the tripodal ligand (11, 11a, 11c), a shift (ΔνCO~ 30cm) of the band assigned to the carbonyl of the ring toward lower frequency upon coordination was observed from 1660–1650 cm−1 for the ligand to 1630–1620 cm−1 for the complexes 12, 12a, 12c. The bi-macrocycle cage 11b was also complexed to Ga(NO3)3 and GdCl3·6H2O. In these complexes the shift for the carbonyl of the ring stretching frequencies in the IR spectra were not as significant as observed with complex Gd(III) 12b and complex Ga(III) 12d. However, the mass spectra and microanalyses confirmed the formation of these complexes. The Gd(III) complexes 12, 12a and 12c appear to be monomeric with the respective ligands 11-11a and 11c bonded in hexadentate coordination modes. This is in contrast to the Gd(III) complex 12b where it is thought that only two HOPO units coordinate the Gd(III) ion, and that the third HOPO moiety assisted with the formation of polymers by coordinating to a second Gd(III) ion. The Ga(III) ion in complex 12d is assumed to be inside the cage of 11b. This conclusion was reached based upon the size of a similar cage (e.g. BC-TREN-TAM) that has been shown to be more appropriate for the incorporation of Ga(III) ion (radius = 76 pm for 6 coordinate) than Gd(III) ion (radius = 119 pm for 8 coordinate) [22, 23].

In conclusion, an optimal synthesis for a key intermediate dithiazolide HOPO 8 has been developed, that supports formation of four new ligands and their formation of Gd(III) and Ga(III) complexes is described. This work is intended to support MRI and PET molecular imaging.

EXPERIMENTAL

General information

Unless otherwise noted, starting materials were obtained from commercial suppliers and used without further purification. All organic extracts were dried over anhydrous MgSO4 and solvents removed in vacuo. Infrared spectra were recorded with the Nicolet 580 spectrophotometer using KBr tablets. 1H spectra were recorded on a Bruker AVB 300 at 300 MHz, a Bruker AVB 400 at 400 MHz, or a Bruker AVB 600 at 600 MHz. 13C spectra were collected using a Bruker AVB 400 at 100 MHz or a Bruker AVB 600 at 150 MHz. The residual solvent peak or TMS was used as an internal reference. Elemental analysis, mass spectrometry (HR = high resolution; ESI-MS = electrospray ionization mass spectrometry), and X-ray diffraction data were obtained at the analytical facilities at the University of California, Berkeley.

Ethyl 3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxylate (3)

In a round bottom flask diethyl oxalacetate (100.0 g, 0.476 mol, 1 eq.) was dissolved in dry tetrahydrofuran (THF) (600 mL). Chloroacetone (47.0 g, 0.50 mol, 1.05 eq.) was added to the reaction mixture and then ammonia gas was bubbled through the mixture (40 min.), resulting in a red mixture. A catalytic quantity of aluminum chloride (AlCl3, 6.44 g, 0.05 mol, 0.09 eq.) was added slowly, and the mixture was stirred (4 days, 23°C). The yellow heterogeneous mixture was centrifuged (6000 rpm, 30 min.), and the resulting yellow solid was quenched using aqueous 6M HCl solution. The solid was collected by filtration and dried in a desiccator to give 3 as a beige solid (18.1 g, 19%). IR (KBr, ν cm−1): 1678 (C=O, ester), 1644 (C=O, ring).1H NMR (300 MHz, CDCl3 + TMS): δ (ppm): 12.77 (s, 1H), 10.77 (s, 1H), 6.53 (s, 1H), 4.42 (q, J = 7.1 Hz, 2H), 2.34 (s, 3H), 1.42 (t, J = 7.1 Hz, 3H); 13C{1H} NMR (400 MHz, CDCl3 + TMS): (δ, ppm): 169.21, 160.18, 150.74, 133.27, 115.40, 102.20, 62.28, 18.63, 14.09. [M+H]+ calcd for C9H12NO4 198.0766, Found 198.0762 m/z.

Ethyl 3-(benzyloxy)-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxylate (4)

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU, 13.6 g, 89.0 mmol, 1.5 eq.) was added to a solution containing 3 (11.5 g, 58.6 mmol, 1 eq.) in isopropanol (200 mL). The reaction mixture was refluxed at 83 °C under N2 before adding benzyl bromide (15.2 g, 88.9 mmol, 1.5 eq.) dropwise. Refluxing was maintained for four hours and then the solvent was evaporated. The resulting dark brown oil was dissolved in dichloromethane (DCM, 30 mL), washed with aqueous 3M HCl solution (2×30 mL), and then with Millipore water (3×30 mL). The organic layers were combined and dried with Na2SO4, and the solvent was evaporated. Diisopropyl ether (250 mL) was added to the oily residue which precipitated after a day and 4 was recovered as a light brown solid (9.43 g, 56%). IR (KBr, ν cm−1):1712 (C=O, ester), 1646(C=O, ring). 1H NMR (300 MHz, CDCl3 + TMS): (δ, ppm): 12.31 (s, 1H), 7.31–7.53 (m, 5H), 6.17 (s, 1H), 5.27 (s, 2H), 4.29 (q, J = 7.1 Hz, 2H), 2.33 (s, 3H), 1.29 (t, J = 7.1 Hz, 3H); 13C{1H} NMR (400 MHz, CDCl3): (δ, ppm): 165.32, 162.20, 144.54, 139.59, 137.26, 133.24, 128.55, 128.27, 128.03, 104.35, 74.01, 61.69, 18.54, 14.11.[M+H]+ calcd for C16H18NO4 288.1236, Found 288.1232 m/z.

Ethyl 3-(benzyloxy)-1-(2-(tert-butoxy)-2-oxoethyl)-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxylate (5)

Dimethoxyethane (5mL) was added under inert conditions to a sample of 4 (0.3 g, 1.04 mmol, 1 eq.) and KF alumina (182 mg, 3.13 mmol, 3 eq.) previously purged with N2. Tert-butyl iodoacetate (182 mg, 3.13 mmol, 3 eq.) was added dropwise under N2. The reaction mixture was heated (2 h, 45 °C) then left to stir (12 h, 23 °C). The alumina was removed by filtration and the filtrate was concentrated to dryness. The residue was purified by flash chromatography using a gradient of MeOH in DCM. The compound (recovered at 5% of MeOH) with the shortest retention time in HPLC C18 was characterized as 5 (146 mg, 35%) and the last eluted was found to be the starting material 4. IR (KBr, ν cm−1):1740 (C=O, ester), 1661 (C=O, ring). 1H NMR (500 MHz, CDCl3): (δ, ppm): 7.49 (d, J = 5.0 Hz, 2H), 7.35 (dd, J = 5.0 Hz, 2H), 7.30 (d, J = 5.0 Hz, 1H), 6.19 (s, 1H), 5.24 (s, 2H), 4.73 (s, 2H), 4.27 (q, J = 7.0 Hz, 2H), 2.38 (s, 3H), 1.48 (s, 9H), 1.27 (t, J = 7.0 Hz, 3H,).13C{1H} NMR (500 MHz, CDCl3) (δ, ppm): 166.5, 165.2, 160.2, 144.9, 139.7, 137.1, 130.3, 128.5, 128.2, 127.9, 104.0, 82.8, 73.8, 61.5, 46.5, 27.9, 20.0, 14.0. [M+H]+ calcd for C22H28NO6: 402.1838, Found 402.1916 m/z. Anal. Calcd (found) for C22H27NO6: C, 65.82 (65.18); H, 6.78 (6.63); N, 3.49 (3.02).

2-(3-(benzyloxy)-4-(ethoxycarbonyl)-6-methyl-2-oxopyridin-1(2H)-yl) acetic acid (6)

Sample of 4 (4.10 g, 14.3 mmol, 1 eq.), magnesium di-tert-butoxide (Mg(OtBu)2, 5.28 g, 31.0 mmol, 2.2 eq.), and potassium tert-butoxide (KOtBu, 1.79 g, 16.0 mmol, 1.1 eq.) were combined in a round bottom flask, purged three times with nitrogen and then THF (200ml) was added. A solution of bromoacetic acid (5.29 g, 38.0 mmol, 2.7 eq.) in dry THF (20 mL) was added dropwise and the reaction mixture was stirred (12 h, 23 °C). The solvent was evaporated, and the dark brown oil was dissolved in dichloromethane (DCM, 30 mL). The mixture was quenched with aqueous 3M HCl solution (2×30 mL) and washed with Millipore water (2×30 mL). The organic layers were collected and dried with Na2SO4, and the solvent was evaporated. Diisopropyl ether was added and the mixture was stirred (12 h, 23 °C) to cause precipitation. The brown solid 6 was collected by filtration and dried to give compound 6 as a beige solid (3.9 g, 80%). IR (KBr, ν cm−1): 1733 (C=O, acid), 1716 (C=O, ester), 1645(C=O, ring). 1H NMR (300 MHz, CDCl3 + TMS): (δ, ppm): 7.28–7.46 (m, 5H), 6.27 (s, 1H), 5.19 (s, 2H), 4.82 (s, 2H), 4.26 (q, J = 7.1 Hz, 2H), 2.26 (s, 3H), 1.28 (t, J = 7.1 Hz, 3H); 13C{1H} NMR (400 MHz, CDCl3 + TMS): (δ, ppm): 170.09, 164.85, 160.94, 144.89, 140.18, 136.92, 131.42, 128.60, 128.27, 128.04, 105.43, 74.24, 61.80, 46.54, 20.15, 14.07. [M-H]− calcd for C18H18NO6 344.1134, Found 344.1147 m/z. Anal. Calcd (found) for C18H19NO6: C, 62.60 (61.45); H, 5.55 (5.69); N, 4.06 (4.16).

Ethyl 3-(benzyloxy)-1-(2-((2,5-dioxopyrrolidin-1-yl)oxy)-2-oxoethyl)-6-methyl-2-oxo-1,2 dihydropyridine-4-carboxylate (6a)

A solution of N-hydroxysuccinimide (NHS, 0.66 g, 5.79 mmol, 2 eq.) and N,N′-dicyclohexylcarbodiimide (DCC, 0.89 g, 4.35 mmol, 1.5 eq.) in dimethylformamide (DMF, 3 mL) was added dropwise to a solution containing 6 (1 g, 2.89 mmol, 1 eq.) in DMF (10 mL) and the mixture was stirred (24 h, 23 °C). The volatile components were removed under vacuum and the residue was dissolved in DCM (20 mL) and water (10 mL). The organic phase was collected and dried over MgSO4 and concentrated until dryness. The residue was crystallized from isopropyl alcohol (10 mL) to give 6a as a white solid (0.78 g, 71%). IR (KBr, ν cm−1): 1707 (C=O, ester), 1648 (C=O, ring). 1H NMR (300MHz, CDCl3): (δ, ppm): 7.31–7.44 (m, 5H), 6.21 (s, 1H), 5.26 (s, 2H,), 5.18 (s, 2H), 4.26 (q, J = 7.1 Hz, 2H), 2.86 (s, 4H), 2.34 (s, 3H), 1.24 (t, J = 7.1 Hz, 3H). Anal. Calcd (found) for C22H22N2O8: C, 59.73 (57.53); H, 5.01 (6.03); N, 6.33 (6.78).

3-(benzyloxy)-1-(carboxymethyl)-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxylic acid (7)

A solution of NaOH (1.33 g, 33.3 mmol, 2.9 eq.) in water (40 mL) was added to a solution containing 6 (3.98 g, 11.5 mmol, 1 eq.) in ethanol (140 mL). The reaction mixture was stirred (1.5 h, 23 °C) and reaction progress was monitored via TLC (DCM:MeOH 9:1). The solvent was evaporated, the resulting dark oil was suspended in ethyl acetate and the solution was concentrated twice to ensure that all the ethanol was removed. The oil was dissolved in water (20 ml) and the flask was placed in an ice bath. Compound 7 was recovered by acidification of the aqueous solution with aqueous 3M HCl solution (50 mL). A light brown precipitate was recovered after stirring (12h, 23°C) then dried to give 7 as a white solid (3.4 g, 98%). IR (KBr, ν (cm−1): 1720 (C=O, acid), 1647 (C=O, ring). 1H NMR (300 MHz, DMSO-d6): (δ, ppm): 7.35–7.49 (m, 5H), 6.25 (s, 1H), 5.09 (s, 2H), 4.79 (s, 2H), 2.31 (s, 3H); 13C{1H} NMR (600 MHz, DMSO-d6): (δ, ppm): 170.30, 167.45, 160.47, 143.48, 142.79, 138.21, 133.18, 129.23, 129.20, 128.95, 103.80, 73.96, 47.10, 20.51. [M+H]+ calcd for C16H16NO6 318.0978 Found 318.0977m/z, [M+Na]+ calcd for C16H15NO6Na 340.0797, Found 340.0804 m/z [M-H]− calcd for C16H14NO6 316.0821, Found 316.0835 m/z. Anal. Calcd (found) for C16H21NO9 (L+3H2O): C, 51.75 (56.46); H, 5.70 (4.90); N, 3.77 (4.12).

3-(benzyloxy)-6-methyl-1-(2-oxo-2-(2-thioxothiazolidin-3-yl)ethyl)-4-(2-thioxothiazolidine-3-carbonyl)pyridin-2(1H)-one (8)

N,N-diisopropylethylamine (DIPEA, 5.00 g, 38.7 mmol, 4.6 eq.) was added dropwise to a suspension of 7 (2.68 g, 8.44 mmol, 1 eq.), O-(Benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium tetrafluoroborate (TBTU, 6.26 g, 19.5 mmol, 2.3 eq.), 4-(dimethylamino)pyridine (DMAP, 0.11 g, 0.925 mmol, 0.11 eq.), and 2-mercaptothiazoline (2.26 g, 19.0 mmol, 2.2 eq.) in DCM (80 mL). After addition, the reaction mixture turned dark brown and it was stirred (40 min., 23°C). The solvent was evaporated and immediately purified using CombiFlash® (gradient of EtOAc in DCM). The fractions were collected at 40% EtOAc, concentrated, and washed with diethyl ether to give 8 as a yellow solid (2.9 g, 66%). IR (KBr, ν cm−1):1699 (C=O amide), 1653 (C=O, ring), 1597 (C=S, thiaz). 1H NMR (300 MHz, CDCl3 + TMS): (δ, ppm): 7.31–7.43 (m, 5H), 6.02 (s, 1H), 5.63 (s, 2H), 5.26 (s, 2H), 4.62 (t, J = 7.5 Hz, 2H), 4.31 (t, J = 7.3 Hz, 2H), 3.42 (t, J = 7.5 Hz, 2H), 2.88 (t, J = 7.3 Hz, 2H), 1.58 (s, 3H). 13C{1H} NMR (400 MHz, CDCl3 + TMS): (δ, ppm): 202.06, 200.79, 168.13, 165.95, 159.22, 141.39, 140.49, 137.57, 132.96, 128.39, 128.33, 128.10, 104.17, 73.87, 55.84, 55.07, 51.29, 29.33, 29.14, 20.47. [M+H]+ calcd for C22H22N3O4S4: 520.0493, Found: 520.0484 m/z. Anal. Calcd (found) for C22H21N3O4S4: C, 50.85 (50.40); H, 4.07 (4.10); N, 8.09 (8.32).

Tert-butyl (2-(2-(3-(benzyloxy)-6-methyl-2-oxo-4-(2-thioxothiazolidine-3-carbonyl)pyridin- 1(2H)-yl)acetamido)ethyl)carbamate (9)

A solution of tert-butyl (2-aminoethyl)carbamate (703 mg, 4.39 mmol, 1.1 eq.) in DCM (40 mL) was added at 1.2 mL/hour using an automated syringe to a solution of 8 (2.00 g, 3.84 mmol, 1 eq.) in DCM (100 mL). The reaction mixture was stirred for four hours after the end of the addition before being concentrated and purified using CombiFlash® (gradient of MeOH in DCM). The fractions were collected (10% MeOH) and evaporated to dryness to give 9 as a light yellow solid (1.87 g, 86%). IR (KBr, ν cm−1): 1697(C=O, ester), 1685 (C=O, amides), 1654 (C=O, ring), 1598 (C=S, thiaz). 1H NMR (300 MHz, CDCl3 + TMS): (δ, ppm): 7.32–7.43 (m, 5H), 6.90 (s, 1H), 6.03 (s, 1H), 5.27 (s, 2H), 4.91 (s, 1H), 4.70 (J = 7.3 Hz, 2H), 2.43 (s, 3H), 1.43 (s, 9H); 13C{1H} NMR (400 MHz, CDCl3 + TMS): (δ, ppm): 200.98, 167.49, 165.76, 159.88, 141.38, 141.28, 137.45, 133.40, 128.44, 128.37, 128.22, 104.75, 79.55, 74.09, 55.07, 50.78, 48.81, 40.30, 29.14, 28.39, 20.52. [M+H]+ calcd for C26H33N4O6S2 561.1842, Found 561.1835 m/z. Anal. Calcd (found) for C26H32N4O6S2: C, 55.70 (55.32); H, 5.75 (4.99); N, 9.99 (9.50).

N,N′,N″-(nitrilotris(ethane-2,1-diyl))tris(2-(3-hydroxy-6-methyl-2-oxo-4-(2-thioxothiazolidine-3-carbonyl)pyridin-1(2H)-yl)acetamide) (9a)

A solution containing TREN (43 mg, 0.29 mmol, 0.53 eq.) and DIPEA (78 mg, 0.60 mmol, 1.1 eq.) in DCM (37 mL) was added at a rate of 1.5 mL/hour using an automated syringe to a solution containing 8 (290 mg, 0.56 mmol, 1 eq.) in DCM (50 mL). The reaction mixture was stirred (12 h, 23 °C), the solvent was evaporated and the mixture purified through CombiFlash® (gradient of MeOH in DCM). The fractions of the column were collected (10% MeOH) and evaporated. The yellow residue was solubilized in a minimum of DCM, followed by a slow precipitation with addition of diethyl ether to give 9a as a yellow solid (143 mg, 57%). IR (KBr, ν cm−1):1700 (C=O, amides), 1655 (C=O, ring), 1600 (C=S, thiaz). 1H NMR (300 MHz, CDCl3 + TMS): (δ, ppm): 8.09 (t, J = 6.2 Hz, 3H), 7.29–7.31 (m, 15H), 5.94 (s, 3H), 5.13 (s, 6H), 4.65 (s, 6H), 4.30 (t, J = 7.3 Hz, 6H), 3.19 (s, 6H), 2.98 (t, J = 7.3 Hz, 6H), 2.53 (s, 6H), 2.17 (s, 9H); 13C{1H} NMR (400 MHz, CDCl3 + TMS): (δ, ppm): δ (ppm): 200.92, 167.01, 175.75, 159.67, 142.12, 141.37, 137.43, 133.46, 128.52, 128.18, 127.79, 104.25, 75.65, 55.24, 50.83, 48.47, 38.54, 29.22, 20.43. [M+H]+ calcd for C63H67N10O12S6 1347.3264, Found 1347.3253 m/z. Anal. Calcd (found) for C63H66N10O12S6: C, 56.15 (55.9); H, 4.94 (5.02); N, 10.39 (10.50).

Tri-tert-butyl (((2,2′,2″-((((nitrilotris(ethane-2,1-diyl))tris(azanediyl))tris(carbonyl))tris(3-(benzyloxy)-6-methyl-2-oxopyridine-4,1(2H)-diyl))tris(acetyl))tris(azanediyl))tris(ethane-2,1-diyl))tricarbamate (10)

A solution of TREN (0.506 g, 3.45 mmol, 0.36 eq.) and DIPEA (1.52 g, 11.2 mmol, 1.2 eq.) in DCM (50 mL) was added at a rate of 1.5 mL/hour via automated syringe to a solution of 9 (5.31 g, 9.47 mmol, 1 eq.) in DCM (120 mL). After complete addition the mixture was stirred (4 h, 23 °C) before being evaporated and purified using CombiFlash® (gradient of MeOH in DCM). The fractions were collected (5% MeOH) and evaporated to give 10 as a white solid (2.28 g, 49%). IR (KBr, ν cm−1): 1691 (C=O, amide), 1677 (C=O, ester), 1658 (C=O, ring). 1H NMR (300 MHz, CDCl3 + TMS): (δ, ppm): 7.77 (s, 3H), 7.43 (s, 3H), 7.28 (s, 15H), 6.60 (s, 3H), 5.13 (s, 6H), 4.72 (s, 6H), 3.38 (s, 6H), 3.27 (s, 6H), 3.01 (s, 3H), 2.39 (s, 9H), 2.24 (s, 6H), 1.41 (s, 27H); 13C{1H} NMR (400 MHz, CDCl3 + TMS): (δ, ppm): 167.44, 163.23, 160.28, 156.65, 143.81, 140.44, 136.25, 130.81, 128.79, 128.73, 128.63, 105.39, 79.53, 74.70, 51.86, 48.40, 40.37, 40.22, 37.24, 28.38, 20.33. [M+Na]+ calcd for C75H99N13O18Na 1492.7129, Found 1492.7120 m/z, [M+H]+ calcd for C75H100N13O18 1470.7311 Found 1470.7312 m/z. Anal. Calcd (found) for C75H99N13O18 + 3H2O: C, 59.08 (58.92); H, 6.94 (6.72); N, 11.94 (11.98).

Tri-tert-butyl (((1,1′,1″-(((nitrilotris(ethane-2,1-diyl))tris(azanediyl))tris(2-oxoethane-2,1-diyl))tris(3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-1,4-diyl-4-carbonyl))tris(azanediyl))tris(ethane-2,1-diyl))tricarbamate (10a)

A solution containing 9a (0.143 g, 0.106 mmol, 1 eq.) in DCM (50 mL) was added dropwise at a rate of 1.5 mL/hour via automated syringe to a solution of DIPEA (69 mg, 0.53 mmol, 5 eq.) and tert-butyl (2-aminoethyl)carbamate (51 mg, 0.32 mmol, 3 eq.) in DCM (20 mL). The solvent was evaporated and the mixture was purified via CombiFlash® (gradient of MeOH in DCM). The fractions were collected (5% MeOH) and evaporated. The recovered clear oil was re-dissolved in a minimal amount of DCM and precipitated by slow addition of diethyl ether to give 10a as a white solid (63 mg, 41%). IR (KBr, ν cm−1):1710 (C=O, amides), 1690 (C=O, ester), 1650 (C=O, ring), 1H NMR (300 MHz, CDCl3 + TMS): (δ, ppm): 8.16 (s, 3H), 7.93 (s, 3H), 7.35 (s, 15H), 6.59 (s, 3H), 5.17 (s, 6H), 5.06 (s, 3H), 4.80 (s, 6H), 3.28 (s, 12H), 3.14 (s, 6H), 2.64 (s, 6H), 2.27 (s, 9H), 1.41 (s, 27H); 13C{1H} NMR (400 MHz, CDCl3 + TMS) (δ, ppm): 166.91, 163.79, 160.30, 156.07, 143.27, 141.01, 136.01, 130.2, 128.94, 128.85, 128.44, 105.59, 79.30, 74.39, 53.77, 48.38, 40.37, 39.82, 38.79, 28.41, 20.35. [M+H]+ calcd for C75H100N13O18 1470.7311, Found 1470.7306 m/z. Anal. Calcd (found) for C75H99N13O18: C, 61.25 (60.62); H, 6.79 (6.81); N, 12.38 (12.04).

Macrocycle BC-TREN-tris-6-Me-3,2-HOPO(Bn) (10b)

A first solution containing 9a (0.34 g, 0.23mmol, 1 eq.) in DCM (25 mL) was prepared. A second solution of TREN (0.03 g, 0.23 mmol, 1 eq.) and DIPEA (0.12 g, 0.93 mmol, 4 eq.) in DCM (25 mL) was also prepared. Both solutions were simultaneously added to DCM (110 mL) at a rate of 1 mL/hour using automated syringes. The reaction was stirred for 1 day after the end of the addition. TLC showed the formation of a single major spot. The reaction mixture was evaporated and purified using CombiFlash® (gradient of MeOH 0.1% N(Et)3 in DCM). The fractions were collected (5% MeOH) and evaporated to give compound 10b as a light beige solid (142 mg, 53%). IR (KBr, ν cm−1):1720 (C=O, amide), 1654(C=O, ring). 1H NMR (300MHz, CD3OD): (δ, ppm): 7.21 (br s, 15H), 6.27 (br s, 3H), 5.20 (br s, 6H), 4.80 (br s, 6H), 3.45 (br s, 6H), 3.05 (br s, 6H), 2.21 (br s, 21H). 13C{1H} NMR (600Mhz, CDCl3 with a drop of MeOH 600MHz): (δ, ppm): 169.0, 163.53, 159.76, 143.23, 140.71, 135.93, 131.10, 128.09 104.0, 74.17, 50.41, 48.22, 38.43, 36.93, 19.74. [M+H] + calcd for C60H70N11O12 1136.5205, Found 1136.5227 m/z. Anal. Calcd (found) for C60H69N11O12: C, 59.6 (53.25); H, 5.92 (6.75); N, 12.74 (13.20).

Diethyl 1,1′-(((((2-(2-(3-(benzyloxy)-4-(ethoxycarbonyl)-6-methyl-2-oxopyridin-1(2H)-yl)-N-methylacetamido)ethyl)azanediyl)bis(ethane-2,1-diyl))bis(azanediyl))bis(2-oxoethane-2,1-diyl))bis(3-(benzyloxy)-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxylate) (10c)

A solution containing DIPEA (90mg, 0.69 mmol, 5 eq.) and tris(2-aminoethyl)amine (TREN, 20 mg, 0.14 mmol, 1 eq.) in DCM (5 mL) was added to a solution of 6a (0.2 g, 0.45 mmol, 3.3 eq.) in dry DCM (5 mL). The reaction mixture was stirred (12h, 23°C) then the organic phase was washed with water (2×5 mL). The organic phase was dried using MgSO4 and concentrated to dryness to give compound 10c as a light beige solid (85 mg, 50%). IR (KBr, ν cm−1): 1731 C=O, ester), 1690 (C=O, amide), 1655 (C=O, ring). 1H NMR (300MHz, CDCl3): (δ, ppm): 7.36–7.38 (m, 2H), 7.23–7.29 (m, 3H), 5.04 (s, 2H), 4.67 (br s, 2H), 4.24 (q, J =7.2 Hz, 2H), 3.21 (br s, 2H), 2.55 (br s, 2H), 2.04 (s, 3H), 1.25 (t, J =7.2 Hz, 3H,). 13C{1H} NMR (CDCl3, 600 MHz): (δ, ppm): 166.89, 164.82, 160.65, 144.70, 141.73, 137.23, 131.20, 128.38, 127.98, 127.73, 104.73, 73.80, 61.66, 52.87, 38.38, 33.96, 20.22, 14.09. [M+H]+ calcd for C60H70N7O15 1128.493, Found: 1128.4914 m/z. Anal. Calcd. (found) for C60C69N7O15: C, 63.87 (64.20); H, 6.16 (5.09); N, 8.69 (8.53).

N,N′,N″-(nitrilotris(ethane-2,1-diyl))tris(1-(2-((2-aminoethyl)amino)-2-oxoethyl)-3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxamide) (11)

A solution containing 10 (231 mg, 0.16 mmol, 1 eq.) in glacial acetic acid (5 mL) and concentrated HCl (5 mL) was added to a DTPA-washed round-bottom flask. The resulting yellow mixture was stirred (12 h, 23 °C) then the solvent was evaporated. The yellow solid was dissolved in a minimal amount of Millipore water and transferred to a centrifuge tube containing diethyl ether. MeOH was added to the biphasic mixture until a white precipitate appeared. The precipitate was centrifuged (6000 rpm, 30 min.), and the process was repeated three times to give 11 as a light yellow crystalline solid (169 mg, 98%). IR (KBr, ν cm−1):1717 (C=O, amide), 1658 (C=O, ring).1H NMR (300 MHz, CD3OD): δ (ppm): 6.44 (s, 2H), 4.83 (br s, 6H), 3.92 (br s, 6H), 3.57 (t, J = 5.7 Hz, 6H), 3.14 (t, J = 5.7 Hz, 6H), 2.27 (s, 9H). 13C{1H} NMR (400 MHz, CDCl3 + TMS): δ (ppm): 167.71, 166.66, 159.17, 145.46, 135.15, 117.24, 102.76, 52.14, 47.54, 38.58, 36.82, 34.52, 19.91. [M+H]+ calcd for C39H58N13O12 900.4328, Found 900.4330 m/z. Anal Calcd for (found) C39H61N13O12Cl4: C, 44.79 (44.32); H, 5.88 (6.51); N, 17.41 (17.02).

1,1′,1″-(((nitrilotris(ethane-2,1-diyl))tris(azanediyl))tris(2-oxoethane-2,1-diyl))tris(N-(2-aminoethyl)-3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxamide) (11a)

A solution containing 10a (148 mg, 0.10 mmol) in glacial acetic acid (2 mL) and concentrated HCl (2 mL) was added to a 25 mL DTPA-washed round-bottom flask. The resulting yellow mixture was stirred (12 h, 23 °C), and then the solvent was evaporated. The yellow solid was dissolved in a minimal amount of Millipore water, and transferred to a centrifuge tube containing diethyl ether. MeOH was added to the biphasic mixture until a white precipitate appeared. The precipitate was centrifuged (6000 rpm, 30 min.), and the process was repeated three times, to give 11a as a light yellow crystalline solid (51 mg, 56%). IR (KBr, ν cm−1): 1691(C=O, amides), 1658 (C=O, ring). 1H NMR (300 MHz, DMSO-d6): (δ, ppm): 8.67 (s, 6H), 8.04 (s, 9H), 6.44 (s, 3H), 4.65 (s, 6H), 3.66, (s, 6H), 3.47 (s, 6H), 3.28 (s, 6H), 2.91(s, 6H), 2.12 (s, 9H).13C{1H} NMR (400 MHz, CDCl3 + TMS): (δ, ppm): 170.24, 167.51, 159.72, 144.29, 136.03, 116.0, 104.58, 54.30, 48.03, 39.12, 37.13, 34.82, 19.07.[M-H]− calcd for C39H56N13O12 898.4171 Found 898.4158 m/z. Anal. Calcd (found) for C39H73Cl4N13O18 (L.4HCl, 6H2O): C, 40.59 (39.05); H, 6.38 (7.10); N, 15.78 (9.60), (very hydroscopic).

Macrocycle BC-TREN-tris-6-Me3,2-HOPO (11b)

A solution containing 10b (142 mg, 0.12 mmol) in concentrated HCl (2 mL) and glacial acetic acid (2 mL) was added to a DTPA-washed round-bottom flask. The reaction was stirred (48 h, 23°C). The solvent was removed and the residue was precipitated using a mixture of water, MeOH and diethyl ether to give compound 11b as a light beige solid (86 mg, 80%). IR (KBr, ν cm−1):1680 (C=O, amides), 1658 (C=O, ring). 1H NMR (300MHz, DMSO-d6): (δ, ppm): 8.65 (OH, br s), 8.45 (NH, br s), 7.87 (NH, br s), 6.35 (3H, s), 4.72 (6H, s), 3.34 (6H,m), 3.10 (6H, m), 2.47(12H, m), 2.09 (9H,s). 13C{1H} NMR (600MHz, DMSO-d6): (δ, ppm): 185.0, 169.7, 159.2, 145.0, 135.6, 117.5, 103.1, 56.5, 46.5, 46.4, 34.8, 34.5, 18.8; [M+H+] calcd for C39H52N11O12 866.3797, Found 866.3792 m/z. Anal Calcd (found) for C39H53N11O12Cl2: C, 49.89 (50.40); H, 5.69 (6.43); N, 16.41 (16.21).

Triethyl-1,1′,1″-(((nitrilotris(ethane-2,1-diyl))tris(azanediyl))tris(2-oxoethane-2,1-diyl))tris(3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxylate) (11c)

A solution containing 10c (140 mg, 0.12 mmol) in glacial acetic acid (1.5 mL) and concentrated HCl (1.5 mL) was added to a DTPA-washed round-bottom flask. The mixture was stirred (12h, 23°C). The solvent was removed, then the residue was solubilized in a minimum of MeOH and a solid was precipitated with diethyl ether. The solid was recovered after centrifugation of the suspension (6000 rpm, 30 min) to give compound 11c as a light beige solid (100 mg, 95%). IR (KBr, ν cm−1): 1700 (C=O, ester), 1685 (C=O amide), 1655(C=O, ring). 1H NMR (300MHz, CDCl3): (δ, ppm): 10.41 (s, 1H), 8.23 (s, 1H), 6.33 (s, 1H), 4.91 (s, 2H), 4.36 (q, 2H), 3.25 (s, 2H), 2.57 (s, 2H), 2.33 (s, 3H), 1.37 (t, 7.2 Hz, 3H). 13C{1H} NMR (600MHz, CDCl3): (δ, ppm): 167.45, 166.03, 159.38, 147.03, 134.67, 114.25, 102.37, 64.84, 61.00, 48.69, 19.71, 14.03, please note that one methylene is under the MeOH peak. [M+H]+ calcd for C39H52H7O15: 858.3521, Found: 858.3528 m/z. Anal Calcd (found) for C39H52N7O15Cl: C, 52.37 (53.01); H, 5.86 (6.06); N, 10.97 (11.62).

Gd(III)-N,N′,N″-(nitrilotris(ethane-2,1-diyl))tris(1-(2-((2-aminoethyl)amino)-2-oxoethyl)-3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxamide) (12)

A solution of gadolinium (III) chloride hexahydrate (GdCl3·6 H2O, 72 mg, 0.19 mmol, 1.5 eq.) in water (2 mL) was added to a solution containing 11 (139 mg, 0.13 mmol, 1 eq.) in Millipore water (5 mL) and placed in a 25 mL DTPA-washed round-bottom flask. Pyridine (497 mg, 6.28 mmol, 47 eq.) was added to the reaction mixture and was refluxed (12h, 95°C). The solvent was evaporated. The solid was dissolved in a minimal amount of MeOH and added to a centrifuge tube containing diethyl ether. The precipitate was recovered after centrifugation (6000 rpm, 30 min.), and the process was repeated three times, to give complex 12 as a light grey solid (160 mg, 98%). IR (KBr, ν (cm−1):1680 (C=O, amides), 1624(C=O, ring). [M+H]+ calcd for C39H55N13O12Gd 1055.3344, Found 1055.3348 m/z Anal. Calcd (found) for C42H73Gd2N10O20Cl3 (GdL(H2O)2 + Gd·Cl3·6H2O): C, 34.58 (31.19); H, 5.04 (5.63); N, 9.60 (10.54).

Gd-1,1′,1″-(((nitrilotris(ethane-2,1-diyl))tris(azanediyl))tris(2-oxoethane-2,1-diyl))tris(N-(2-aminoethyl)-3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxamide) (12a)

A solution of GdCl3·6 H2O (2.31 mg, 6.22 mmol, 1 eq.) in Millipore water (1 mL) was added to 11a (6.51 mg, 6.22 mmol, 1 eq.) in MeOH (5ml). Pyridine (20 μL) was then added and the reaction mixture was stirred (24 h, 95°C). After cooling, the complex was recovered by precipitation using a minimum of MeOH and addition of diethyl ether until a white precipitate appeared. The precipitate was washed three times with diethyl ether and recovered after centrifugation (6000 rpm, 30 min), to give complex 12a as a light grey solid (6 mg 91%). IR (KBr, ν (cm−1): 1690 (C=O, amide), 1624 (C=O, ring). [M+H]+ calcd for C39H55N13O12Gd 1055.3256, Found 1055.3338 m/z. Anal. Calcd (found) for C39H58N13O17Gd3 (LGd(H2O) + Gd2O3): C, 32.24 (32.04); H, 4.02 (5.33); N, 12.53 (11.06).

Gd-BC-TREN-tris-6-Me3,2-HOPO (12b)

A solution of GdCl3·6 H2O (4.29 mg, 0.01 mmol, 1eq.) in MeOH (2 mL) was added to a solution containing 11b (10 mg, 0.01 mmol, 1 eq.) in MeOH (5 mL), followed by the addition of pyridine (4.25 mg, 0.03 mmol, 3 eq.). The reaction was stirred (24 h, 95°C), then the solvent was removed and the residue was precipitated in a minimum of MeOH with a slow addition of diethyl ether to give complex 12b as a white grey solid (6 mg, 48%). IR (KBr, ν (cm−1):1682 (C=O, amides), 1650 (C=O, ring). [M-H]− calcd for C39H48ClN11O12Gd (L−3Gd+3Cl) 1055.2413, Found 1055.2395 m/z; [M-H]− calcd for C39H50ClN11O13Gd (L−3Gd+3Cl.H2O) 1073.2519, Found 1073.2487 m/z. Anal. Calcd (found) for C40H66N10O20GdCl5 (L−2Gd−32Cl 2H2O + GdCl3·6H2O): C, 32.05 (31.85); H, 4.44 (5.27); N, 9.35 (8.74).

Gd-triethyl-1,1′,1″-(((nitrilotris(ethane-2,1-diyl))tris(azanediyl))tris(2-oxoethane-2,1-diyl))tris(3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxylate) (12c)

A solution of GdCl3·6H2O (40 mg, 0.011 mmol, 1 eq.) in MeOH (5 mL) was added to a solution containing 11c (94 mg, 0.11 mmol, 1 eq.) in MeOH (1 mL), followed by the addition of pyridine (40 mg, 0.326 mmol, 3 eq.). The reaction mixture was stirred (24 h, 95°C). After cooling, the complex was recovered in a minimum of MeOH by slow addition of diethyl ether. The precipitate was washed three times with diethyl ether and recovered after centrifugation (6000 rpm, 30 min) to give complex 12c as a white solid (85 mg, 60 %). IR (KBr, ν (cm−1): 1700 (C=O, ester), 1650 (C=O, amide) 1567 (C=O, ring). [M+H]+ calcd for C39H51Gd2N7O16Cl3 1294.0928, Found 1294.0776 m/z, Anal. Calcd (found) for C39H50Gd2N7O16Cl3: C, 36.20 (32.78); H, 3.90 (5.01); N, 7.72 (7.67).

Ga-BC-TREN-tris-6-Me3,2-HOPO (12d)

A solution of Ga(acetyl acetate) (Ga-Acac 8.48 mg, 0.02 mmol,1 eq.) in MeOH (2 mL) was added to a solution of 11b (20 mg, 0.02 mmol, 1 eq) in MeOH (5 mL) and water (2 mL) followed by the addition of pyridine (131 mg, 1.66 mmol, 72 eq.). The reaction mixture was stirred (24 h, 95 °C). The solvent was removed and the residue was precipitated using a minimum of MeOH and slow addition of diethyl ether. The solid was recovered after centrifugation (6000 rpm, 30 min) to a give 12d as a white powder (8 mg, 36%). IR (KBr, ν (cm−1): 1654 (C=O, amide), 1648 (C=O, ring). [M+H]+ calcd. for C39H49N11O12Ga 932.2812, Found 932.2822 m/z, [M+H+H2O]+ calcd. For C39H50N11O13Ga 950.2924, Found 950.2931 m/z, [M+H+2H2O]+ calcd. for C39H52N11O14Ga 968.3029, Found 968.3042 m/z. Anal. Calcd (found) for C39H64GaN11O26. [LGa+ Ga(OH)4. 2H2O]: C, 33.90 (33.08); H, 4.67 (5.14); N, 11.15 (10.11).

Acknowledgments

This work was supported by NIH (HL069832). The authors wish to thank the mass spectrometry facility (Dr. Andersen Ulla and Dr. Nichiporuck Rita) and the X-ray facility (Dr. Antonio DiPasquale), for their help in collecting the respective data and for interpretation of the X-ray diffraction data. The authors thank Professor Richmond Sarpong for the use of the IR spectrometer and Dr. Jide Xu for scientific discussions.

References and Notes

  • 1.Santos MA, Marques SM, Chaves S. Coord Chem Rev. 2012;256:240. [Google Scholar]
  • 2.Telpoukhovskaia MA, Rodriguez C, Cawthray JF, Scott LE, Page BDG, Ali-Torres J, Sodupe M, Bailey GA, Patrick BO, Orvig C. Metallomics. 2014;6:249. doi: 10.1039/c3mt00135k. [DOI] [PubMed] [Google Scholar]; Evans RW, Kong X, Hider RC. Biochim Biophys Acta, General Subjects. 2012;1820:282. doi: 10.1016/j.bbagen.2011.11.007. [DOI] [PubMed] [Google Scholar]
  • 3.Puerta DT, Lewis JA, Cohen SM. J Am Chem Soc. 2004;126 doi: 10.1021/ja0485513. [DOI] [PubMed] [Google Scholar]; Rangel M, Joao A, MN, Ana Leite A, Pereira E, deCastro B, Sousa C, Yoshikawa Y, Sakurai H. J Inorg Biochem. 2009;103:496. doi: 10.1016/j.jinorgbio.2008.12.019. [DOI] [PubMed] [Google Scholar]
  • 4.Reichert DE, Lewis JS, Anderson CJ. Coord Chem Rev. 1999;184:3. [Google Scholar]; Chang PY, Bunin DI, Gow J, Swezey R, Shinn W, Shuh DK, Abergel RJ. J Chromatograph Separat Techniq. 2013;4:196. [Google Scholar]
  • 5.Moore EG, Xu J, Jocher CJ, Corneillie J, TM, Raymond KN. Inorg Chem. 2010;49:9928. doi: 10.1021/ic101133w. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Moore EG, Samuel APS, Raymond KN. Acc Chem Res. 2009;42:542. doi: 10.1021/ar800211j. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Raymond KN, Pierre VC. Bionconjugate Chem. 2005;16:3. doi: 10.1021/bc049817y. [DOI] [PubMed] [Google Scholar]
  • 8.Werner EJ, Avedano S, Botta M, Hay BP, Moore EG, Aime S, Raymond KN. J Am Chem Soc. 2007;129:1870. doi: 10.1021/ja068026z. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9.Werner EJ, Botta M, Aime S, Raymond KN. Contrast Media Mol Imaging. 2009;4:220. doi: 10.1002/cmmi.281. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Thompson MK, Doble DMJ, Tso LS, Barra S, Botta M, Aime S, Raymond KN. Inorg, Chem. 2004;43:8577. doi: 10.1021/ic048607u. [DOI] [PubMed] [Google Scholar]; Thompson MK, Missellwitz BL, Tso S, Doble DMJ, Schmitt-Willich H, Raymond KN. J Med Chem. 2005;48:3874. doi: 10.1021/jm049041m. [DOI] [PubMed] [Google Scholar]
  • 11.Pierre VC, Botta M, Raymond KN. J Am Chem Soc. 2005;127:504. doi: 10.1021/ja045263y. [DOI] [PubMed] [Google Scholar]
  • 12.Floyd WC, III, Klemm PJ, Smiles DE, Kohlgruber AC, Pierre VC, Mynar JL, Frechet JM, Raymond KN. J Am Chem Soc. 2011;133:2390. doi: 10.1021/ja110582e. [DOI] [PMC free article] [PubMed] [Google Scholar]; Praveena GD, Datta A, Dante RW, Raymond KN, Francis MB. J Am Chem Soc. 2011;133:14704. doi: 10.1021/ja204516p. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 13.Doble DMJ, Melchior M, O’Sullivan B, Siering C, Xu J, Pierre VC, Raymond KN. Inorg Chem. 2003;42:4930. doi: 10.1021/ic026240s. [DOI] [PubMed] [Google Scholar]; Butlin NG, Raymond KN, Xu J, D’Aleo A. WO 2011025790 A1 20110303 PCT Int Appl. 2011; Sanderson PE, Lyle TA, Dorsey BD, Stanton MG, Staas D, Coburn C, Naylor-Olsen AM, Morrissette MM, Selnick HG, Nanterment PG, Williams PD, Stauffer KJ, Burgey C, Isaacs R. WO 2000026211 A1 20000511 PCT Int Appl. 2000
  • 14.Pierre VC, Melchior M, Doble DMJ, Raymond KN. Inorg Chem. 2004;43:8520. doi: 10.1021/ic0493447. [DOI] [PubMed] [Google Scholar]
  • 15.Arumugam J, Brown HA, Jacobs HK, Gopalan AS. Synthesis. 2011;1:57. doi: 10.1055/s-0030-1258337. [DOI] [PMC free article] [PubMed] [Google Scholar]; Martinez G, Arumugam J, Jacobs HK, Gopalan AS. Tetrahedron Letters. 2013;54:630. doi: 10.1016/j.tetlet.2012.11.136. [DOI] [PMC free article] [PubMed] [Google Scholar]; Liu Y, Jacobs HK, Gopalan AS. J Org Chem. 2009;74:782. doi: 10.1021/jo802410u. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Schmidtchen FP, Rapoport H. J Am Chem Soc. 1977;99:7014. doi: 10.1021/ja00463a041. [DOI] [PubMed] [Google Scholar]; Kaval N, Ermolat’ev D, Appukkuttan P, Dehaen W, Kappe OC, Van der Eycken E. J Comb Chem. 2005;7:490. doi: 10.1021/cc0498377. [DOI] [PubMed] [Google Scholar]
  • 17.Feist D. Chem Ber. 1902;35:1540. [Google Scholar]
  • 18.Nishi T, Tabusa F, Tanaka, Ueda T, Shimizu HT, Kanbe T, Kimura Y, Nakagawa K. Chem Pharma Bull. 1983;31:852. doi: 10.1248/cpb.31.852. [DOI] [PubMed] [Google Scholar]
  • 19.Guo ZX, Cammidge AN, Mckillop A, Horwell DC. Tetrahedron Lett. 1999;40:6999. [Google Scholar]
  • 20.Fang YQ, Bio MM, Hansen KB, Potter MS, Clausen A. J Am Chem Soc. 2010;132:15525. doi: 10.1021/ja107709w. [DOI] [PubMed] [Google Scholar]
  • 21.Garrett TM, Mc Murry TJ, Hosseini MW, Reyes ZE, Hahn FE, Raymond KN. J Am Chem Soc. 1991;113:2965. [Google Scholar]; Albrecht M, Franklin SJ, Raymond KN. Inorg Chem. 1994;33:5785. [Google Scholar]
  • 22.http://www.webelements.com

RESOURCES