Design, Synthesis, and Antiviral Activity of Novel Ribonucleosides of 1,2,3‐Triazolylbenzyl‐aminophosphonates

Abstract

A novel series of ribonucleosides of 1,2,3‐triazolylbenzyl‐aminophosphonates was synthesized through the Kabachnik–Fields reaction using I₂ as catalyst followed by copper‐catalyzed cycloaddition of the azide–alkyne reaction (CuAAC). All structures of the newly prepared compounds were characterized by ¹H NMR, ¹³C NMR, and HRMS spectra. The structures of 2e, 2f, 3d, and 3g were further confirmed by X‐ray diffraction analysis. These compounds were tested against various strains of DNA and RNA viruses; compounds 4b and 4c showed a modest inhibitory activity against respiratory syncytial virus (RSV) and compound 4h displayed modest inhibitory activity against Coxsackie virus B4.

Introduction

Currently, most of the human beings in the world suffer from different kinds of diseases caused by DNA and RNA viruses. These diseases are mostly diagnosed but difficult to cure. Vaccination is a reliable tool to fight viral diseases, but it is only available against few viruses. The difficulties associated with national or worldwide vaccination programs make antiviral chemotherapy an even more practical approach in the fight against epidemic viral infections. Nucleoside analogs are synthetic compounds that are structurally similar to natural nucleosides and can serve as building blocks of DNA and RNA. They can act as competitive inhibitors of viral and cellular DNA and RNA polymerases or alternatively can be incorporated into growing DNA and RNA strands causing chain termination 1.

α‐Aminophosphonates are defined as structural analogs of natural amino acids. They are considered as an important class of compounds with diverse and interesting biological activities. Some of the aminophosphonates were described as anticancer agents 2, enzyme inhibitors 3, peptide mimetics 4, antibiotics and pharmacological agents 5. They have also been reported to be interesting carriers for the transport of hydrophilic molecules across bilayer lipid membranes 6. The α‐aminophosphonate derivatives are often synthesized via the Kabachnik–Fields reaction by coupling of a carbonyl compound, an amine, and a hydroxyphosphoryl compound using various catalysts 7, 8, 9.

1,2,3‐Triazoles were prepared by Huisgen in the 1960s 10 using the 1,3‐dipolar cycloaddition reaction with acetylenes. After approximately four decades, this reaction has acquired considerable attention owing to the introduction of copper(I) as catalyst by Medal and then by Sharpless 11, 12, 13. The copper‐catalyzed cycloaddition of azides and alkynes (CuAAC) also known as “click chemistry” offers a simple access to the 1,4‐isomer in very short reaction times.

Further, nucleosides containing 1,2,3‐triazole ring have been of special interest in drug development research. Some synthetic triazoles have displayed interesting biological activities and several analogs have been tested against hepatitis C and HIV‐1 viruses 14, 15, 16, 17, 18. Moreover, nucleoside and acyclonucleoside analogs containing 1,2,3‐triazole and phosphonate structures have been described as potent antiviral agents 19, 20, 21.

Herein, we describe the synthesis of novel hybrid molecules containing triazolyl‐nucleoside linked to α‐aminophosphonates by a phenyl ring. The choice of these structures is based on the combination of both pharmacophore parts, the phenyl‐triazolyl‐riboside and the α‐aminophosphonates, which are known to have significant pharmacological properties. Our synthesis strategy is based on the use of two reactions: Kabachnick–Fields reaction and 1,3‐dipolar cycloaddition. The compounds obtained were tested against selected DNA and RNA viruses.

Results and discussion

Chemistry

The synthesis of the desired compounds (4a–j and 5a–j) is depicted in Scheme 1. Initially, the α‐aminophosphonate compounds were prepared in good yields via the Kabachnik–Fields reaction. The 4‐[(trimethylsilyl)ethynyl]benzaldehyde 1 was reacted with diethylphosphite and corresponding amine in acetonitrile using molecular iodine as catalyst 22, 23, 24. The latter is low‐priced, readily available, non‐metallic, and non‐toxic. The mixture was stirred at room temperature for 1 h to get compounds 2a–j. The next step is deprotection of the trimethylsilyl group. For this purpose, tetrabutylammonium fluoride (TBAF) in tetrahydrofurane (THF) was used to give the terminal alkyne 25. The structures of 2e, 2f, 3d, and 3g were confirmed by X‐ray diffraction (Fig. 1). According to the crystal data, the structures are similar for these compounds. The P—C bond has a staggered conformation, with the two six‐membered groups with respect to the P=O double bond. The two benzene rings are almost perpendicular in all four compounds. In each crystal structure (2e, 3d, and 3g), the molecules are arranged as centrosymmetric or pseudocentrosymmetric dimers related by two N—H⋯O=P hydrogen bonds. On the other hand, in the crystal structure of 2f, the hydrogen bond N—H⋯O=P is not found, and the molecules are arranged as centrosymmetric dimers linked by C_methyl—H⋯O=P hydrogen bonds 26.

Scheme 1.

Reagents and conditions: (i) R‐NH₂ (1.2 equiv.), H(O)P(OEt)₂ (1.2 equiv.), I₂ (0.2 equiv.), MeCN, r.t., 1 h; (ii) TBAF (1 equiv.), THF, r.t., 30 min; (iii) azido‐ribose (2.5 equiv.), CuI (0.1 equiv.), Et₃N (1.1 equiv.), MWI, 5 min; (iv) MeONa (1 equiv.), MeOH, r.t., 30 min.

Figure 1.

X‐ray crystallographic structures of compounds 2e, 2f, 3d, and 3g. Displacement ellipsoids are drawn at the 50% probability level.

Next, the 1,2,3‐triazolyl‐nucleosides were prepared using the 1,3‐dipolar cycloaddition reaction. For this, the terminal alkynes 3a–j and β‐azido‐ribose 27 were coupled using the Cu alkyne‐azide cycloaddition in basic medium (triethylamine) and the reaction was carried out under microwave irradiation 28. Microwave heating has been shown to increase reaction yields and to speed up reaction time 29, β‐azido‐ribose is slightly unstable under micro‐wave conditions and was used in excess. The configuration at the anomeric carbon C1′ is retained as it is present in the β‐azido‐ribose. The hydroxyl functions were protected by benzoyl groups prior to the CuAAC reaction in order to increase the solubility of the compounds. The structures of all compounds were confirmed on the basis of ¹H, ¹³C NMR spectra as well as by high‐resolution mass spectrometry. In the ¹H NMR spectra of the intermediates, the triazole proton appears as a singlet in the aromatic region while the anomeric proton appears as a multiplet around 6 ppm.

The last step involves the removal of the benzoyl protecting groups from O2′, O3′, and O5′ positions of D‐ribose 4a–j using sodium methoxide (NaOMe) in methanol 30 to afford the desired 1,2,3‐triazole nucleosides 5a–j (Table 1).

Table 1.

Results of protected (4a–j) and deprotected (5a–j) triazolo nucleoside phosphonates. 

Entry	R	Compounda)	Yieldb) (%)	Compounda)	Yieldc) (%)
1		4a	95	5a	98
2		4b	90	5b	99
3		4c	92	5c	98
4		4d	94	5d	99
5		4e	75	5e	95
6		4f	89	5f	98
7		4g	90	5g	98
8		4h	78	5h	95
9		4i	84	5i	96
10		4j	80	5j	97

^a)All products were characterized by ¹H NMR, ¹³C NMR, and mass spectrometry.

^b)Yields of isolated products for the CuAAC reaction.

^c)Yields of isolated products for the protection reaction.

Biological testing

The antiviral activities of the synthesized compounds (4a–j, 5a–j) were tested against different viruses: HIV‐1 and HIV‐2 in MT4 cell cultures; herpes simplex virus‐1 (HSV‐1) (Kos strain), herpes simplex virus‐2 (HSV‐2) (G strain), HSV‐1 thymidine kinase deficient, acyclovir‐resistant (TK⁻ Kos, ACV^r), vaccinia virus, vesicular stomatitis virus (VSV), adenovirus‐2, varicella‐zoster virus (VZV) (Oka strain and TK⁻ 07/1 strain), human cytomegalovirus (HCMV) (AD‐169 and Davis strain) in human embryonic lung (HEL) cells; VSV, Coxsackie virus B4, and respiratory syncytial virus (RSV) in HeLa cells; parainfluenza‐3 virus, reovirus‐1, Sindbis virus, Coxsackie virus B4, and Punta Toro virus in Vero cells; feline corona virus (FIPV) and feline herpes virus in Crandell‐Rees Feline Kidney (CRFK) cells, influenza A H1N1 subtype, influenza A H3N2 subtype, and influenza B virus in MDCK (Madin–Darby canine kidney) cells. The following reference compounds were included: tenofovir (PMPA), AMD3100, ganciclovir, cidofovir, acyclovir, brivudin, the lectins Hippeastrum hybrid agglutinin (HHA) and Urtica dioica agglutinin (UDA), dextran sulfate (molecular weight 10000, DS‐10000), ribavirin, oseltamivir carboxylate, amantadine and rimantadine, zalcitabine and alovudine. The antiviral activity was expressed as the EC₅₀: the compound concentration required to reduce virus‐induced cytopathogenicity or viral plaque formation by 50%. The cytotoxicity of the tested compounds toward the uninfected host cells was defined as the minimum cytotoxic concentration (MCC) that causes a microscopically detectable alteration of normal cell morphology. The 50% cytotoxic concentration (CC₅₀), causing a 50% decrease in cell viability was determined using a colorimetric 3‐(4,5‐dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxyphenyl)‐2‐(4‐sulfophenyl)‐2H‐tetrazolium (MTS) assay system.

The tested compounds (4a–j, 5a–j) displayed no antiviral activity against the different viruses tested except for compounds 4b and 4c that showed a slight inhibition of respiratory syncytial virus replication (Table 2) and compounds 5c, 5f, and 5g that displayed weak activity against both TK⁺ and TK⁻ VZV strains (see Supporting Information). Although compound 4h had some activity against Coxsackie virus B4 in Vero cell cultures, no activity was seen in HeLa cells (Tables 2 and 3).

Table 2.

Cytotoxicity and antiviral activity of some compounds in HeLa cell cultures. 

Compound	Minimum cytotoxic concentrationa) (μM)	EC50 b) (μM)
		Vesicular stomatitis virus	Coxsackie virus B4	Respiratory syncytial virus
4a	>50	>50	>50	>50
4b	>100	>100	>100	47.5 ± 3.5
4c	>100	>100	>100	51.5 ± 9.2
4d	>100	>100	>100	≥72.5 ± 38.9
5i	20	>4	>4	>4
5j	≥20	>20	>20	>20
DS‐10.000 (μg/mL)	>100	12	>100	1.3 ± 0.7
Ribavirin	>250	22	146	2.9 ± 1.3

^a)Required to cause a microscopically detectable alteration of normal cell morphology.

^b)Required to reduce virus‐induced cytopathogenicity by 50%.

Table 3.

Cytotoxicity and antiviral activity of 4h in Vero cell cultures. 

Compound	Minimum cytotoxic concentrationa) (μM)	EC50 b) (μM)
		Parainfluenza‐3 virus	Reovirus‐1	Sindbis virus	Coxsackie virus B4	Punta Toro virus
4h	>100	>100	>100	>100	20	>100
DS‐10.000 (μg/mL)	>100	>100	>100	8.9	>100	8.9
Ribavirin	>250	85	>250	>250	>250	112

^a)Required to cause a microscopically detectable alteration of normal cell morphology.

^b)Required to reduce virus‐induced cytopathogenicity by 50%.

Conclusion

A series of novel 1,2,3‐triazolyl ribosides linked to α‐aminophosphonates (4a–j, 5a–j) were successfully prepared in high yield via the Kabachnik–Fields reaction and a Cu(I)‐catalyzed alkyne‐azide cycloaddition under microwave irradiation. The synthesized compounds were evaluated against a broad range of DNA and RNA viruses, some of them showing modest activity against respiratory syncytial virus (compounds 4b and 4c) and varicella‐zoster virus (compounds 5c, 5f, and 5g).

Experimental

Chemistry

General

Reactions were carried out in a microwave oven model AVM510/WP/WH. Reactions were monitored by thin layer chromatography (TLC) on precoated silica gel 60 F254 (Merck, Darmstadt, Germany); UV light was used for visualization of the spots. All products were purified by column chromatography on silica gel (100–200 mesh; Merck). ¹H NMR and ¹³C NMR spectra were recorded on a Bruker 300 and 75 MHz spectrometer, respectively, SiMe₄ was used as internal standard. Chemical shifts are given in ppm and coupling constants (J) in MHz and multiplicity is reported as s (singlet), d (doublet), t (triplet), q (quartet), and m (multiplet). Mass spectra were produced by ESI/MS and MALDI‐TOF‐MS.

General procedure for the synthesis of diethyl [(4‐(2‐(trimethylsilyl)ethynyl)phenyl)(aryl or alkylamino)methyl]phosphonates 2a–j

The compounds 2a–j were synthesized by reaction of commercial (Sigma–Aldrich) 4‐[(trimethylsilyl)ethynyl]benzaldehyde 1 (1 mmol), diethylphosphite (1.2 equiv.), and corresponding amine (1.2 equiv.) in acetonitrile (3 mL) using molecular iodine (0.2 equiv.) as catalyst at room temperature, the reaction mixture was stirred at room temperature for 1 h. Then, the solvent was removed under reduced pressure. The resulting residue was purified by column chromatography using ethyl acetate/hexane as eluent.

Diethyl [(4‐(2‐(trimethylsilyl)ethynyl)phenyl)(phenylamino)methyl]phosphonate 2a

Yield: 95%; Rf: 0.40; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.22 (s, 9H, —CH₃), 1.06 (t, 3H, —CH₃, J = 6.9 Hz), 1.20 (t, 3H, —CH₃, J = 6.9 Hz), 3.60–3.68 (m, 1H, —OCH₂—), 3.83–3.92 (m, 1H, —OCH₂—), 3.97–4.08 (m, 2H, —OCH₂—), 4.62 (d, 1H, CHP, J = 23.7 Hz), 5.17 (s, 1H, NH), 6.47 (d, 2H, Ar—H, J = 8.1 Hz), 6.61 (t, 1H, Ar—H, J = 7.2 Hz), 7.01 (t, 2H, Ar—H, J = 7.8 Hz), 7.33–738 (m, 4H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.06 (Si—CH₃), 16.32–16.58 (CH₃), 55.20 (CHP), 63.43–63.52 (CH₂), 94.74, 104.86 (≡C—), 114.01, 118.69, 127.84, 129.28, 132.26 (phenyl—CH), 122.81, 136.76, 146.35 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₂₂H₃₀NO₃PSi: 415.54, found: 417.00; HRMS (M+K): calcd. for C₂₂H₃₀NO₃PSiK: 454.13642, found: 454.13539.

Diethyl [2‐chlorophenylamino][(4‐(2‐(trimethylsilyl)ethynyl)phenyl]methylphosphonate 2b

Yield: 90%; Rf: 0.45; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.10 (s, 9H, —CH₃), 1.02 (t, 3H, —CH₃, J = 6.9 Hz), 1.10 (t, 3H, —CH₃, J = 6.9 Hz), 3.56 (m, 1H, —OCH₂—), 3.81 (m, 1H, —OCH₂—), 3.95 (m, 2H, —OCH₂—), 4.54 (d, 1H, CHP, J = 24.3 Hz), 5.14 (br s, 1H, NH), 6.15 (d, 1H, Ar—H, J = 7.8 Hz), 6.63 (t, 1H, Ar—H, J = 7.2 Hz), 6.71 (t, 2H, Ar—H, J = 7.5 Hz), 6.93–7.19 (m, 4H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.00 (Si—CH₃), 16.07–16.50 (CH₃), 54.99 (CHP), 63.15–63.68 (CH₂), 94.83, 104.76 (≡C—), 112.73, 117.82, 118.78, 122.42, 127.06, 127.70, 129.39, 132.46 (phenyl—CH), 122.96 (C—Cl), 120.08, 136.06, 142.29 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₂₂H₂₉ClNO₃PSi: 449.98, found: 451.00; HRMS (M+K): calcd. for C₂₂H₂₉ClNO₃PSiK: 488.09744, found: 488.09631.

Diethyl [2‐bromophenylamino][(4‐(2‐(trimethylsilyl)ethynyl)phenyl]methylphosphonate 2c

Yield: 89%; Rf: 0.45; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.10 (s, 9H, —CH₃), 0.99 (t, 3H, —CH₃, J = 7.2 Hz), 1.07 (t, 3H, —CH₃, J = 7.2 Hz), 3.57 (m, 1H, —OCH₂—), 3.76 (m, 1H, —OCH₂—), 3.91 (m, 2H, —OCH₂—), 4.54 (d, 1H, CHP, J = 24.6 Hz), 5.21 (br s, 1H, NH), 6.12 (d, 1H, Ar—H, J = 8.1 Hz), 6.63 (t, 1H, Ar—H, J = 7.5 Hz), 6.71 (t, 2H, Ar—H, J = 7.5 Hz), 7.15–7.29 (m, 4H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.00 (Si—CH₃), 16.30–16.52 (CH₃), 55.20 (CHP), 63.43–63.72 (CH₂), 94.83, 104.76 (≡C—), 110.57 (C—Br), 112.77, 119.27, 127.60, 128.36, 132.46–132.52 (phenyl—CH), 122.87, 135.91, 143.07 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₂₂H₂₉BrNO₃PSi: 494.43, found: 496.00; HRMS (M+Na): calcd. for C₂₂H₂₉BrNO₃PSiNa: 516.07299, found: 516.07122.

Diethyl [4‐bromophenylamino][(4‐(2‐(trimethylsilyl)ethynyl)phenyl]methylphosphonate 2d

Yield: 92%; Rf: 0.40; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.02 (s, 9H, —CH₃), 0.92 (t, 3H, —CH₃, J = 6.3 Hz), 1.02 (t, 3H, —CH₃, J = 6.3 Hz), 3.49 (m, 1H, —OCH₂—), 3.71 (m, 1H, —OCH₂—), 3.88 (m, 2H, —OCH₂—), 4.42 (d, 1H, CHP, J = 24.3 Hz), 4.65 (br s, 1H, NH), 6.17 (d, 2H, Ar—H, J = 9.0 Hz), 6.93 (d, 2H, Ar—H, J = 8.7 Hz), 7.12 (d, 2H, Ar—H, J = 8.1 Hz), 7.19 (d, 2H, Ar—H, J = 8.1 Hz). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.00 (Si—CH₃), 16.28–16.53 (CH₃), 55.15 (CHP), 63.44–63.67 (CH₂), 94.98, 104.62 (≡C—), 110.49 (C—Br), 115.58, 127.70, 131.98–132.36 (phenyl—CH), 122.95, 136.02, 145.11 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₂₂H₂₉BrNO₃PSi: 494.43, found: 494.90; HRMS (M+Na): calcd. for C₂₂H₂₉BrNO₃PSiNa: 516.07299, found: 516.07251.

Diethyl [4‐fluorophenylamino][(4‐(2‐(trimethylsilyl)ethynyl)phenyl]methylphosphonate 2e

Yield: 77%; Rf: 0.36; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.01 (s, 9H, —CH₃), 0.91 (t, 3H, —CH₃, J = 6.7 Hz), 1.07 (t, 3H, —CH₃, J = 6.7 Hz), 3.44 (m, 1H, —OCH₂—), 3.74 (m, 1H, —OCH₂—), 3.87 (m, 2H, —OCH₂—), 4.44 (d, 1H, CHP, J = 24.3 Hz), 5.20 (br s, 1H, NH), 6.25 (d, 2H, Ar—H, J = 6.6 Hz), 6.55 (d, 2H, Ar—H, J = 6.6 Hz), 7.15–7.22 (m, 4H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.00 (Si—CH₃), 16.25–16.51 (CH₃), 55.73 (CHP), 63.55–63.64 (CH₂), 94.87, 104.70 (≡C—), 114.95–115.84, 127.82, 132.31 (phenyl—CH), 122.87, 136.32, 142.58 (phenyl—C), 154.84 (C—F). ESI‐MS (M+H), m/z calcd. for C₂₂H₂₉FNO₃PSi: 433.53, found: 434.80; HRMS (M+K): calcd. for C₂₂H₂₉FNO₃PSiK: 472.12699, found: 472.12658.

Diethyl [4‐chloro‐2‐methylphenylamino][(4‐(2‐(trimethylsilyl)ethynyl)phenyl]methylphosphonate 2f

Yield: 87%; Rf: 0.43; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.01 (s, 9H, —CH₃), 0.89 (t, 3H, —CH₃, J = 6.9 Hz), 1.02 (t, 3H, —CH₃, J = 6.9 Hz), 1.99 (s, 3H, Ar—CH₃), 3.48 (m, 1H, —OCH₂—), 3.72 (m, 1H, —OCH₂—), 3.86 (m, 2H, —OCH₂—), 4.43 (d, 1H, CHP, J = 24.6 Hz), 4.54 (s, 1H, NH), 6.00 (d, 1H, Ar—H, J = 8.4 Hz), 6.93 (d, 1H, Ar—H, J = 8.4 Hz), 6.76 (s, 1H, Ar—H), 7.14–7.22 (m, 4H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.00 (Si—CH₃), 16.26–16.51, 17.38 (CH₃), 55.26 (CHP), 63.40–63.53 (CH₂), 94.81, 104.74 (≡C—), 124.81 (C—Cl), 112.56, 126.58, 127.59, 129.96–132.28 (phenyl—CH), 122.90, 136.27, 142.92 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₂₃H₃₁ClNO₃PSi: 464.01, found: 465.10; HRMS (M+K): calcd. for C₂₃H₃₁ClNO₃PSiK: 502,11309, found: 502.11199.

Diethyl (4‐(2‐(trimethylsilyl)ethynyl)phenyl)(2‐naphthalenylamino)methylphosphonate 2g

Yield: 88%; Rf: 0.50; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.26 (s, 9H, —CH₃), 1.18 (t, 3H, —CH₃, J = 6.9 Hz), 1.31 (t, 3H, —CH₃, J = 6.9 Hz), 3.78 (m, 1H, —OCH₂—), 4.01 (m, 1H, —OCH₂—), 4.15 (m, 2H, —OCH₂—), 4.94 (d, 1H, CHP, J = 24.3 Hz), 6.10 (br s, 1H, NH), 6.69 (s, 1H, Ar—H), 6.61 (d, 1H, Ar—H, J = 7.2 Hz), 7.20–7.74 (m, 9H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.00 (Si—CH₃), 16.13–16.52 (CH₃), 55.09 (CHP), 63.00–63.64 (CH₂), 94.77, 104.80 (≡C—), 106.48, 118.16, 122.80, 126.12, 127.69–132.30 (phenyl—CH), 123.97, 126.85, 134.74, 136.43, 143.99 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₂₆H₃₂NO₃PSi: 465.60, found: 467.20; HRMS (M+Na): calcd. for C₂₆H₃₂NO₃PSiNa: 488.17813, found: 488.17658.

Diethyl (benzylamino)(4‐(2‐(trimethylsilyl)ethynyl)phenyl)methylphosphonate 2h

Yield: 78%; Rf: 0.50; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.70 (s, 9H, —CH₃), 0.97 (t, 3H, —CH₃, J = 6.9 Hz), 1.10 (t, 3H, —CH₃, J = 6.9 Hz), 2.27 (br s, 1H, NH), 3.31 (d, 1H, CHP, J = 24.5 Hz), 3.64 (m, 2H, —CH₂—NH—), 3.78–3.98 (m, 4H, —OCH₂—), 7.04–7.13 (m, 5H, Ar—H), 7.20 (d, 2H, Ar—H, J = 8.1 Hz), 7.33 (d, 2H, Ar—H, J = 8.1 Hz). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.06 (Si—CH₃), 16.25–16.48 (CH₃), 51.08 (CH₂—N), 58.40 (CHP), 61.75–63.10 (CH₂), 94.54, 104.87 (≡C—), 127.22, 128.33–132.08 (phenyl—CH), 122.65, 136.42–139.10 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₂₃H₃₂NO₃PSi: 429.56, found: 431.00; HRMS (M+H): calcd. for C₂₃H₃₂NO₃PSi: 430.19618, found: 430.19647.

Diethyl (dodecylamino)(4‐(2‐(trimethylsilyl)ethynyl)phenyl)methylphosphonate 2i

Yield: 88%; Rf: 0.40; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.07 (s, 9H, —CH₃), 0.63 (m, 6H, —OCH₂CH₃, —CH₃), 0.87–1.24 (m, 23H, —CH₂—, —OCH₂CH₃), 2.25 (m, 2H, —CH₂—NH—), 3.18 (br s, 1H, NH), 3.68–3.93 (m, 4H, —OCH₂—), 5.26 (d, 1H, CHP, J = 23.4 Hz), 7.17 (d, 2H, Ar—H, J = 8.2 Hz), 7.59 (d, 2H, Ar—H, J = 8.2 Hz). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.00 (Si—CH₃), 14.00, 16.25–16.48 (CH₃), 22.50, 27.00, 29.11–37.56 (CH₂), 59.56 (CHP), 63.09–63.25 (CH₂), 94.54, 104.87 (≡C—), 128.64, 132.05 (phenyl—CH), 123.06, 135.00 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₂₈H₅₀NO₃PSi: 507.76, found: 509.40; HRMS (M+H): calcd. for C₂₈H₅₀NO₃PSi: 508.33703, found: 508.33659.

Diethyl (octadecylamino)(4‐(2‐(trimethylsilyl)ethynyl)phenyl)methylphosphonate 2j

Yield: 86%; Rf: 0.40; Eluent: ethyl acetate/hexane, 7:3 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.25 (t, 9H, —CH₃), 0.86 (m, 6H, —OCH₂CH₃, —CH₃), 1.05–1.70 (m, 35H, —CH₂—, —OCH₂CH₃), 2.53 (m, 2H, —CH₂—NH—), 3.43 (br s, 1H, NH), 3.78–4.16 (m, 4H, —OCH₂—, CHP), 7.36 (d, 2H, Ar—H, J = 8.2 Hz), 7.62 (d, 2H, Ar—H, J = 8.2 Hz). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 0.00 (Si—CH₃), 14.19, 16.00–16.50 (CH₃), 22.74, 26.88–27.23, 29.51–30.30, 32.06, 29.11–37.56 (CH₂), 59.50 (CHP), 63.00–63.50 (CH₂), 94.50, 104.00 (≡C—), 128.50, 132.00 (phenyl—CH), 123.00, 135.00 (phenyl—C). ESI‐MS (M+H), m/z calcd. for C₃₄H₆₂NO₃PSi: 591.92, found: 593.50; HRMS (M+H): calcd. for C₃₄H₆₂NO₃PSi: 592.43093, found: 592.42999.

General procedure for the synthesis of diethyl [(4‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)(aryl or alkylamino)(phenyl)methyl]phosphonates 4a–j

The trimethylsilyl ethynyl phenyl α‐aminophosphonates 2 (0.7 mmol) were reacted with tetrabutylammonium fluoride (1 equiv.) in tetrahydrofurane (2.5 mL). After 30 min of stirring at room temperature, the reaction mixture was purified by silica gel column chromatography to get ethynyl phenyl α‐aminophosphonates (3a–j).

The terminal alkyne 3 (0.5 mmol) and β‐azido‐ribose (2.5 equiv.) and triethyl amine (1.1 equiv.) were mixed with CuI (0.1 equiv.). The reaction mixture was homogenized in dry acetonitrile (1 mL) and stirred for 5 min. The solvent was evaporated under vacuum. The reaction mixture was then irradiated at the power level 400 W for 2–5 min. The residue was purified on silica gel using ethyl acetate/hexane as eluent.

Diethyl [(4‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(phenylamino)methyl]phosphonate 4a

Yield: 95%; Rf: 0.45; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.11 (t, 3H, —CH₃, J = 6.9 Hz), 1.26 (t, 3H, —CH₃, J = 6.9 Hz), 3.72 (m, 1H, —OCH₂—), 3.95 (m, 1H, —OCH₂—), 4.11 (m, 2H, —OCH₂—), 4.60 (m, 1H, H_5′), 4.77 (d, 1H, CHP, J = 25.2 Hz), 4.85–4.91 (m, 1H, H_5′,H_4′, H_3′, NH), 6.16 (m, 1H, H_2′), 6.30 (m, 1H, H_1′), 6.53–6.74 (m, 4H, Ar—H), 7.13 (m, 2H, Ar—H), 7.31–7.68 (m, 12H, Ar—H, CH—triazole), 7.89–8.08 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 15.54, 15.80 (CH₃), 54.30 (CHP), 62.64–62.76 (C5′, CH₂), 70.87 (C2′), 74.61 (C3′), 80.58 (C4′), 89.73 (C1′), 113.26, 117.87, 125.30, 127.86, 128.52, 129.13, 133.05 (phenyl—CH, triazole—CH), 135.51, 145.66, 147.22 (phenyl—C, triazole—C), 164.37, 164.48, 165.40 (CO). ESI‐MS (M+H), m/z calcd. for C₄₅H₄₃N₄O₁₀P: 830.82, found: 831.40; HRMS (M+K): calcd. for C₄₅H₄₃N₄O₁₀PK: 869.23484, found: 869.23435.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(2‐chlorophenylamino)methyl]phosphonate 4b

Yield: 90%; Rf: 0.45; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.12 (t, 3H, —CH₃, J = 6.9 Hz), 1.29 (t, 3H, —CH₃, J = 6.9 Hz), 3.70 (m, 1H, —OCH₂—), 3.81 (m, 1H, —OCH₂—), 3.95–4.23 (m, 2H, —OCH₂—), 4.61 (m, 1H, H_5′), 4.77–4.90 (m, 3H, CHP, H_5′,H_4′), 5.45 (m, 1H, H_3′), 5.70 (br s, 1H, NH), 6.17 (m, 1H, H_2′), 6.30 (m, 1H, H_1′), 6.46–6.66 (m, 3H, Ar—H), 6.86–6.98 (m, 2H, Ar—H), 7.15–7.67 (m, 12H, Ar—H, CH—triazole), 7.88–8.05 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.25, 16.48 (CH₃), 54.85 (CHP), 63.15–63.64 (C5′, CH₂), 71.56 (C2′), 75.29 (C3′), 81.21 (C4′), 90.41 (C1′), 112.76, 117.66, 118.67, 122.33, 126.03, 128.18, 128.64, 129.35, 133.73 (phenyl—CH, triazole—CH), 120.09 (C—Cl), 135.56, 142.19, 147.78 (phenyl—C, triazole—C), 165.36, 165.40, 166.47 (CO). ESI‐MS (M+H), m/z calcd. for C₄₅H₄₂ClN₄O₁₀P: 865.26, found: 865.50; HRMS (M+K): calcd. for C₄₅H₄₂ClN₄O₁₀PK: 903.19587, found: 903.19617.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(2‐bromophenylamino)methyl]phosphonate 4c

Yield: 92%; Rf: 0.45; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.09–1.25 (t, 6H, —CH₃), 3.79 (m, 1H, —OCH₂—), 3.92 (m, 1H, —OCH₂—), 3.94–3.99 (m, 2H, —OCH₂—), 4.52 (m, 1H, H_5′), 4.67–4.82 (m, 4H, CHP, NH, H_5′,H_4′), 5.45 (m, 1H, H_3′), 6.04 (m, 1H, H_2′), 6.19 (m, 1H, H_1′), 6.33–6.66 (m, 3H, Ar—H), 6.94 (m, 2H, Ar—H), 7.19–7.46 (m, 12H, Ar—H, CH—triazole), 7.79–8.03 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.27, 16.50 (CH₃), 55.08 (CHP), 63.43–63.69 (C5′, CH₂), 71.55 (C2′), 75.24 (C3′), 81.27 (C4′), 90.41 (C1′), 110.59 (C—Br), 112.81, 118.53, 119.16, 126.05, 128.12–129.89, 132.51, 133.50 (phenyl—CH, triazole—CH), 135.52, 143.19–147.83 (phenyl—C, triazole—C), 165.04–166.08 (CO). ESI‐MS (M+H), m/z calcd. for C₄₅H₄₂BrN₄O₁₀P: 909.71, found: 910.70; HRMS (M+K): calcd. for C₄₅H₄₂BrN₄O₁₀PK: 947.14535, found: 947.14589.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(4‐bromophenylamino)methyl]phosphonate 4d

Yield: 94%; Rf: 0.45; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.11 (t, 3H, —CH₃, J = 6.3 Hz), 1.29 (t, 3H, —CH₃, J = 6.3 Hz), 3.69 (m, 1H, —OCH₂—), 3.93 (m, 1H, —OCH₂—), 4.12 (m, 2H, —OCH₂—), 4.59 (m, 1H, H_5′), 4.70 (d, 1H, CHP, J = 24.3 Hz), 4.78–4.89 (m, 3H, H_5′, H_4′, H_3′), 5.20 (br s, 1H, NH), 6.17 (m, 1H, H_2′), 6.31 (m, 1H, H_1′), 6.54 (m, 3H, Ar—H), 7.15 (m, 2H, Ar—H), 7.31–7.63 (m, 12H, Ar—H, CH—triazole), 7.85–8.07 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.21, 16.48 (CH₃), 54.85 (CHP), 63.38–63.60 (C5′, CH₂), 71.59 (C2′), 75.25 (C3′), 81.20 (C4′), 90.41 (C1′), 110.16 (C—Br), 115.56, 118.82, 126.03, 128.27–129.86, 131.87, 133.71 (phenyl—CH, triazole—CH), 135.67, 145.32–147.74 (phenyl—C, triazole—C), 165.04–166.06 (CO). ESI‐MS (M+H), m/z calcd. for C₄₅H₄₂BrN₄O₁₀P: 909.71, found: 911.30; HRMS (M+Na): calcd. for C₄₅H₄₂BrN₄O₁₀PNa: 931.17141, found: 931.17355.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(4‐fluorophenylamino)methyl]phosphonate 4e

Yield: 75%; Rf: 0.40; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.12 (t, 3H, —CH₃, J = 6.9 Hz), 1.30 (t, 3H, —CH₃, J = 6.9 Hz), 3.72 (m, 1H, —OCH₂—), 3.97 (m, 1H, —OCH₂—), 4.13 (m, 2H, —OCH₂—), 4.60 (m, 1H, H_5′), 4.78–4.89 (m, 4H, CHP, H_5′, H_4′, H_3′), 5.15 (br s, 1H, NH), 6.16 (m, 1H, H_2′), 6.30 (m, 1H, H_1′), 6.54 (m, 3H, Ar—H), 6.82 (m, 2H, Ar—H), 7.32–7.67 (m, 12H, Ar—H, CH—triazole), 7.91–8.10 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.22–16.48 (CH₃), 55.60 (CHP), 63.33–63.51 (C5′, CH₂), 71.59 (C2′), 75.28 (C3′), 81.25 (C4′), 90.42 (C1′), 114.88–115.81, 118.63, 126.03, 128.28–129.88, 133.45, 133.88 (phenyl—CH, triazole—CH), 135.96, 142.46–147.83 (phenyl—C), 154.76 (triazole—C), 157.89 (C—F), 165.06–166.08 (CO). ESI‐MS (M+H), m/z calcd. for C₄₅H₄₂FN₄O₁₀P: 848.81, found: 849.10; HRMS (M+K): calcd. for C₄₅H₄₂FN₄O₁₀PK: 887.22542, found: 887.22670.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(4‐chloro‐2‐methylphenylamino)methyl]phosphonate 4f

Yield: 89%; Rf: 0.40; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.13 (t, 3H, —CH₃, J = 6.9 Hz), 1.29 (t, 3H, —CH₃, J = 6.9 Hz), 2.28 (s, 3H, Ar—CH₃), 3.75 (m, 1H, —OCH₂—), 3.98 (m, 1H, —OCH₂—), 4.15 (m, 2H, —OCH₂—), 4.59 (m, 1H, H_5′), 4.63–4.90 (m, 4H, CHP, H_5′, H_4′, H_3′), 5.10 (br s, 1H, NH), 6.17 (m, 1H, H_2′), 6.30 (m, 2H, Ar—H), 6.54 (m, 1H, H_1′), 6.91 (d, 1H, Ar—H, J = 8.4 Hz), 7.03 (s, 1H, Ar—H), 7.33–7.65 (m, 12H, Ar—H, CH—triazole), 7.90–8.05 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.23–16.49, 17.40 (CH₃), 55.13 (CHP), 60.35, 63.36–63.46 (C5′, CH₂), 71.59 (C2′), 75.25 (C3′), 81.22 (C4′), 90.41 (C1′), 112.52, 118.72, 126.05, 128.07–129.94, 133.43–133.87 (phenyl—CH, triazole—CH), 122.80 (C—Cl), 135.79–142.99 (phenyl—C), 147.76 (triazole—C), 165.04–166.06 (CO). ESI‐MS (M+H), m/z calcd. for C₄₆H₄₄ClN₄O₁₀P: 879.29, found: 880.00; HRMS (M+K): calcd. for C₄₆H₄₄ClN₄O₁₀PK: 917.21206, found: 917.21196.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(2‐naphthalenylamino)methyl]phosphonate 4g

Yield: 90%; Rf: 0.45; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.98 (t, 3H, —CH₃, J = 6.9 Hz), 1.19 (t, 3H, —CH₃, J = 6.9 Hz), 3.61 (m, 1H, —OCH₂—), 3.84 (m, 1H, —OCH₂—), 4.03 (m, 2H, —OCH₂—), 4.45 (m, 1H, H_5′), 4.65–4.88 (m, 3H, CHP, H_5′, H_4′), 5.19 (br s, 1H, NH), 6.03 (m, 1H, H_3′), 6.19 (m, 1H, H_2′), 6.38 (d, 1H, H_1′, J = 3.3 Hz), 6.61 (s, 1H, Ar—H), 6.90–7.53 (m, 19H, Ar—H, CH—triazole), 7.76–7.89 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.33–16.51 (CH₃), 54.91 (CHP), 56.91, 63.45–63.59 (C5′, CH₂), 71.59 (C2′), 75.26 (C3′), 81.21 (C4′), 90.41 (C1′), 106.50, 118.20, 118.78, 122.51, 126.34, 127.58–129.88, 133.43–133.86 (phenyl—CH, triazole—CH), 134.78, 136.00, 143.92–144.12 (phenyl—C), 147.84 (triazole—C), 165.03–166.06 (CO). ESI‐MS (M+H), m/z calcd. for C₄₉H₄₅N₄O₁₀P: 880.88, found: 882.00; HRMS (M+H): calcd. for C₄₉H₄₅N₄O₁₀P: 919.25049, found: 919.24998.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(benzylamino)methyl]phosphonate 4h

Yield: 78%; Rf: 0.40; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.08 (t, 3H, —CH₃, J = 6.9 Hz), 1.21 (t, 3H, —CH₃, J = 6.9 Hz), 3.06 (br s, 1H, NH), 3.48 (d, 1H, CHP, J = 23.4 Hz), 3.72 (m, 2H, —CH₂—NH—), 3.76–4.02 (m, 4H, —OCH₂—), 4.55 (m, 1H, H_5′), 4.77–4.82 (m, 2H, H_4′, H_5′), 6.06 (m, 1H, H_3′), 6.21 (m, 1H, H_2′), 6.46 (m, 1H, H_1′, J = 3.6 Hz), 7.17–7.47 (m, 16H, Ar—H, CH—triazole), 7.60 (d, 2H, Ar—H, J = 7.8 Hz), 7.76–7.89 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.32–16.48 (CH₃), 51.28 (CHP), 62.92–63.57 (C5′, CH₂), 71.64 (C2′), 75.28 (C3′), 81.26 (C4′), 90.42 (C1′), 118.56, 125.89, 127.18, 128.36–129.89, 133.47–133.88 (phenyl—CH, triazole—CH), 135.50, 139.19 (phenyl—C), 148.01 (triazole—C), 165.07–166.09 (CO). ESI‐MS (M+H), m/z calcd. for C₄₆H₄₅N₄O₁₀P: 844.84, found: 845.40; HRMS (M+K): calcd. for C₄₆H₄₅N₄O₁₀PK: 883.25049, found: 883.24988.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(dodecylamino)methyl]phosphonate 4i

Yield: 84%; Rf: 0.50; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.68 (t, 3H, —CH₃, J = 6.6 Hz), 0.97 (t, 3H, —CH₃, J = 6.9 Hz), 0.99–1.32 (m, 23H, —CH₃, —CH₂—), 2.31 (m, 2H, —CH₂—NH—), 3.01 (br s, 1H, NH), 3.67 (m, 1H, —OCH₂—), 3.73–3.99 (m, 4H, —OCH₂—, CHP), 4.42 (m, 1H, H_5′), 4.77–4.82 (m, 2H, H_4′, H_5′), 5.97 (m, 1H, H_3′), 6.11 (m, 1H, H_2′), 6.45 (d, 1H, H_1′, J = 4.0 Hz), 7.19–7.44 (m, 13H, Ar—H, CH—triazole), 7.77–7.89 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 14.50, 16.32–16.47 (CH₃), 22.50, 27.00, 28.72–33.87, 40.21 (CH₂), 55.00 (CHP), 63.00–63.49 (C5′, CH₂), 71.59 (C2′), 75.28 (C3′), 81.31 (C4′), 90.48 (C1′), 119.16, 124.79, 125.71, 126.50, 127.42–133.88 (phenyl—CH, triazole—CH), 135.88–136.76 (phenyl—C), 147.50 (triazole—C), 165.00–166.00 (CO). ESI‐MS (M+H), m/z calcd. for C₅₁H₆₃N₄O₁₀P: 923.04, found: 924.00.

Diethyl [(4‐(1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(octadecylamino)methyl]phosphonate 4j

Yield: 80%; Rf: 0.50; Eluent: ethyl acetate/hexane, 8:2 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.77 (t, 3H, —CH₃, J = 6.6 Hz), 1.06–1.41 (m, 38H, —CH₃, —CH₂—), 2.39 (m, 2H, —CH₂—NH—), 3.05 (br s, 1H, NH), 3.73 (m, 1H, —OCH₂—), 3.84–4.01 (m, 4H, —OCH₂—, CHP), 4.53 (m, 1H, H_5′), 4.80–4.91 (m, 2H, H_4′, H_5′), 6.06 (m, 1H, H_3′), 6.21 (m, 1H, H_2′), 6.47 (d, 1H, H_1′, J = 4.0 Hz), 7.30–7.55 (m, 13H, Ar—H, CH—triazole), 7.88–8.00 (m, 7H, Ar—H). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 14.10, 16.33–16.47 (CH₃), 22.67, 27.18, 29.34–29.82, 31.91, 48.60 (CH₂), 59.50 (CHP), 63.01–63.55 (C5′, CH₂), 71.64 (C2′), 75.27 (C3′), 81.28 (C4′), 90.40 (C1′), 118.40, 125.76, 128.53–129.89, 133.46–133.86 (phenyl—CH, triazole—CH), 135.00 (phenyl—C), 149.00 (triazole—C), 165.05–166.04 (CO). ESI‐MS (M+H), m/z calcd. for C₅₇H₇₅N₄O₁₀P: 1007.20, found: 1007.90; HRMS (M+K): calcd. for C₅₇H₇₅N₄O₁₀PK: 1045.48524, found: 1045.48309.

General procedure for the synthesis of diethyl [(4‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)(aryl or alkylamino)(phenyl)methyl]phosphonates 5a–j

To a solution of 1,2,3‐triazole nucleoside analogs 4 (0.45 mmol) in dry methanol (2.5 mL), sodium methoxide (1 equiv.) was added. The reaction mixture was stirred at room temperature until the reaction was complete (30 min). The neutralization was performed with AmberliteIR120 hydrogen form. Afterwards the residue was filtered and evaporated. The crude product was purified by flash silica gel chromatography.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(phenylamino)methyl]phosphonate 5a

Yield: 98%; Rf: 0.30; Eluent: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.98–1.18 (m, 6H, —CH₃), 3.61 (m, 1H, H‐5′A), 3.69–3.86 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.93–4.02 (m, 4H, —OCH₂—, H‐2′,3′), 4.12 (d, 1H, —OH, J = 5.3 Hz), 4.40 (t, 1H, —OH, J = 5.0 Hz), 4.54 (d, 1H, —OH, J = 5.3 Hz), 4.68 (d, 1H, CHP, J = 24.6 Hz), 4.95 (br s, 1H, NH), 5.93 (d, 1H, H‐1′, J = 6.3 Hz), 6.51–6.58 (m, 3H, Ar—H), 6.98 (t, 2H, Ar—H, J = 7.5 Hz), 7.30 (m, 2H, Ar—H), 7.42 (d, 2H, Ar—H, J = 7.5 Hz), 7.82 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.15–16.41 (CH₃), 54.55 (CHP), 61.88–63.79 (C5′, CH₂), 70.87 (C2′), 75.99 (C3′), 85.84 (C4′), 92.88 (C1′), 113.95, 118.60, 120.00, 125.86, 128.36–129.52 (phenyl—CH, triazole—CH), 135.79, 146.11–146.73 (phenyl—C, triazole—C). ESI‐MS (M+H), m/z calcd. for C₂₄H₃₁N₄O₇P: 518.50, found: 520.00; HRMS (M+K): calcd. for C₂₄H₃₁N₄O₇PK: 557.15619, found: 557.15544.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(2‐chlorophenylamino)methyl]phosphonate 5b

Yield: 99%; Rf: 0.32; Eluent: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.08–1.26 (m, 6H, —CH₃), 3.57–3.61 (m, 1H, H‐5′A), 3.69–3.79 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.84–4.07 (m, 4H, —OCH₂—, H‐2′,3′), 4.11 (d, 1H, —OH, J = 5.3 Hz), 4.38 (t, 1H, —OH, J = 5.0 Hz), 4.52 (d, 1H, —OH, J = 5.3 Hz), 4.72 (d, 1H, CHP, J = 24.6 Hz), 5.24 (br s, 1H, NH), 6.01 (d, 1H, H‐1′, J = 6.3 Hz), 6.43 (d, 1H, Ar—H, J = 8.1 Hz), 6.58 (d, 1H, Ar—H, J = 6.3 Hz), 6.93 (t, 1H, Ar—H, J = 7.2 Hz), 7.20 (m, 1H, Ar—H), 7.47 (t, 2H, Ar—H, J = 6.6 Hz), 7.51 (m, 2H, Ar—H), 7.98 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.01–16.41 (CH₃), 54.50 (CHP), 61.85–63.94 (C5′, CH₂), 70.90 (C2′), 76.03 (C3′), 85.89 (C4′), 92.95 (C1′), 112.75, 117.63, 118.84, 120.01, 122.39, 125.97, 127.76–128.12, 129.26, 133.73 (phenyl—CH, triazole—CH), 120.09 (C—Cl), 129.73, 135.17, 141.96 (phenyl—C), 146.68 (triazole—C). ESI‐MS (M+H), m/z calcd. for C₂₄H₃₀ClN₄O₇P: 552.94, found: 553.80; HRMS (M+K): calcd. for C₂₄H₃₀ClN₄O₇PK: 591.11722, found: 591.11690.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(2‐bromophenylamino)methyl]phosphonate 5c

Yield: 98%; Rf: 0.30; Eluent: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.10–1.20 (m, 6H, —CH₃), 3.59–3.62 (m, 1H, H‐5′A), 3.71–3.88 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.90–4.06 (m, 4H, —OCH₂—, H‐2′,3′), 4.11 (d, 1H, —OH, J = 5.3 Hz), 4.39 (t, 1H, —OH, J = 5.0 Hz), 4.51 (d, 1H, —OH, J = 5.3 Hz), 4.76 (d, 1H, CHP, J = 19.8 Hz), 5.25 (br s, 1H, NH), 5.78 (d, 1H, H‐1′, J = 6.3 Hz), 6.34 (d, 1H, Ar—H, J = 7.2 Hz), 6.43 (t, 1H, Ar—H, J = 7.3 Hz), 6.91 (t, 1H, Ar—H, J = 7.8 Hz), 7.19 (m, 3H, Ar—H), 7.47 (m, 2H, Ar—H), 7.65 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.23–16.46 (CH₃), 54.77 (CHP), 61.87–64.07 (C5′, CH₂), 70.90 (C2′), 76.09 (C3′), 85.95 (C4′), 93.04 (C1′), 110.55 (C—Br), 112.81, 119.36, 119.86, 125.99, 128.17–128.43, 132.52 (phenyl—CH, triazole—CH), 129.74, 135.14, 145.95 (phenyl—C), 146.71 (triazole—C). ESI‐MS (M+H), m/z calcd. for C₂₄H₃₀BrN₄O₇P: 597.40, found: 598.00; HRMS (M+K): calcd. for C₂₄H₃₀BrN₄O₇PK: 635.06671, found: 635.06660.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(4‐bromophenylamino)methyl]phosphonate 5d

Yield: 99%; Rf: 0.33; Eluent: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 1.02–1.27 (m, 6H, —CH₃), 3.65 (m, 1H, H‐5′A), 3.68–3.79 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.84–4.14 (m, 4H, —OCH₂—, H‐2′,3′), 4.21 (d, 1H, —OH, J = 5.3 Hz), 4.48 (t, 1H, —OH, J = 5.0 Hz), 4.66 (d, 1H, —OH, J = 5.3 Hz), 4.74 (d, 1H, CHP, J = 25.2 Hz), 5.25 (br s, 1H, NH), 6.04 (d, 1H, H‐1′, J = 6.2 Hz), 6.49 (d, 2H, Ar—H, J = 8.4 Hz), 7.12 (d, 2H, Ar—H, J = 8.4 Hz), 7.37 (d, 2H, Ar—H, J = 8.0 Hz), 7.53 (d, 2H, Ar—H, J = 7.6 Hz), 8.04 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.15–16.41 (CH₃), 56.48 (CHP), 61.91–63.80 (C5′, CH₂), 70.86 (C2′), 75.92 (C3′), 85.75 (C4′), 92.82 (C1′), 110.14 (C—Br), 115.54, 120.14, 125.92, 128.38, 131.87 (phenyl—CH, triazole—CH), 129.63, 135.39, 145.47 (phenyl—C), 146.74 (triazole—C). ESI‐MS (M+H), m/z calcd. for C₂₄H₃₀BrN₄O₇P: 597.40, found: 598.10; HRMS (M+K): calcd. for C₂₄H₃₀BrN₄O₇PK: 635.06671, found: 635.06616.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(4‐fluorophenylamino)methyl]phosphonate 5e

Yield: 95%; Rf: 0.35; Eluent: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.78–1.18 (m, 6H, —CH₃), 3.60 (m, 1H, H‐5′A), 3.62–3.87 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.93–4.06 (m, 4H, —OCH₂—, H‐2′,3′), 4.11 (d, 1H, —OH, J = 5.3 Hz), 4.39 (t, 1H, —OH, J = 5.0 Hz), 4.55 (d, 1H, —OH, J = 6.2 Hz), 4.63 (d, 1H, CHP, J = 24.6 Hz), 5.29 (br s, 1H, NH), 5.95 (d, 1H, H‐1′, J = 6.4 Hz), 6.46 (d, 2H, Ar—H, J = 8.0 Hz), 6.66 (d, 2H, Ar—H, J = 8.1 Hz), 7.28 (d, 2H, Ar—H, J = 7.6 Hz), 7.44 (d, 2H, Ar—H, J = 7.5 Hz), 7.93 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.10–16.37 (CH₃), 55.14 (CHP), 61.88–63.75 (C5′, CH₂), 70.86 (C2′), 75.96 (C3′), 85.80 (C4′), 92.86 (C1′), 114.89–115.78, 120.07, 125.88, 128.39 (phenyl—CH, triazole—CH), 129.60, 135.65, 142.62 (phenyl—C), 146.75 (triazole—C), 154.67 (C—F). ESI‐MS (M+H), m/z calcd. for C₂₄H₃₀FN₄O₇P: 536.49, found: 538.10; HRMS (M+K): calcd. for C₂₄H₃₀FN₄O₇PK: 575.14677, found: 575.14637.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(4‐chloro‐2‐methylphenylamino)methyl]phosphonate 5f

Yield: 98%; Rf: 0.30; Eluent: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.83–1.02 (m, 6H, —CH₃), 1.96 (s, 3H, Ar—CH₃), 3.49 (m, 1H, H‐5′A), 3.50–3.68 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.71–4.84 (m, 4H, —OCH₂—, H‐2′,3′), 3.94 (d, 1H, —OH, J = 5.0 Hz), 4.12 (t, 1H, —OH, J = 7.0 Hz), 4.21 (d, 1H, —OH, J = 5.0 Hz), 4.36 (br s, 1H, NH), 4.50 (d, 1H, CHP, J = 24.6 Hz), 5.76 (d, 1H, H‐1′, J = 7.6 Hz), 6.02 (d, 2H, Ar—H, J = 8.5 Hz), 6.60 (d, 2H, Ar—H, J = 7.2 Hz), 6.73 (s, 1H, Ar—H), 7.13 (d, 2H, Ar—H, J = 6.6 Hz), 7.32 (d, 2H, Ar—H, J = 6.3 Hz), 7.77 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.29–16.53, 17.45 (CH₃), 54.89 (CHP), 62.01–63.85 (C5′, CH₂), 70.97 (C2′), 76.09 (C3′), 85.93 (C4′), 92.99 (C1′), 112.58, 120.14, 126.07, 126.65, 128.19, 130.10 (phenyl—CH, triazole—CH), 123.00 (C—Cl), 125.01,129.81, 135.52, 142.91 (phenyl—C), 146.83 (triazole—C). ESI‐MS (M+H), m/z calcd. for C₂₅H₃₂ClN₄O₇P: 566.97, found: 568.10; HRMS (M+K): calcd. for C₂₅H₃₂ClN₄O₇PK: 605.13287, found: 605.13238.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(2‐naphthalenylamino)methyl]phosphonate 5g

Yield: 98%; Rf: 0.35; Eluent: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.99–1.38 (m, 6H, —CH₃), 3.65 (m, 1H, H‐5′A), 3.70–3.86 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.96–4.08 (m, 4H, —OCH₂—, H‐2′,3′), 4.18 (d, 1H, —OH, J = 5.4 Hz), 4.46 (t, 1H, —OH, J = 5.3 Hz), 4.61 (d, 1H, —OH, J = 6.0 Hz), 4.90 (d, 1H, CHP, J = 24.0 Hz), 5.35 (br s, 1H, NH), 5.99 (d, 1H, H‐1′, J = 6.6 Hz), 6.72 (s, 1H, Ar—H), 7.01 (d, 1H, Ar—H, J = 8.1 Hz), 7.10 (t, 1H, Ar—H, J = 6.9 Hz), 7.28 (dd, 1H, Ar—H, J = 7.2, 2.1 Hz), 7.39–7.56 (m, 7H, Ar—H), 7.86 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.10–16.38 (CH₃), 54.46 (CHP), 61.89, 63.54–63.84 (C5′, CH₂), 70.84 (C2′), 75.89 (C3′), 85.74 (C4′), 92.79 (C1′), 106.27, 118.16, 120.05, 122.52, 125.83–126.39, 127.54, 128.31, 129.07 (phenyl—CH, triazole—CH), 127.86, 134.68, 135.56, 143.88, 144.06 (phenyl—C), 146.69 (triazole—C). ESI‐MS (M+H), m/z calcd. for C₂₈H₃₃N₄O₇P: 568.56, found: 570.20; HRMS (M+K): calcd. for C₂₈H₃₃N₄O₇PK: 607.17184, found: 607.17152.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(benzylamino)methyl]phosphonate 5h

Yield: 95%; Rf: 0.30; Eluent: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.83–1.02 (m, 6H, —CH₃), 2.57 (br s, 1H, NH), 3.27 (m, 2H, —CH₂—NH—), 3.57 (m, 1H, H‐5′A), 3.60–3.71 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.73–3.83 (m, 4H, —OCH₂—, H‐2′,3′), 3.98 (d, 1H, —OH, J = 5.0 Hz), 4.24 (t, 1H, —OH, J = 4.9 Hz), 4.38 (d, 1H, —OH, J = 6.2 Hz), 4.76 (d, 1H, CHP, J = 24.6 Hz), 5.83 (d, 1H, H‐1′, J = 6.3 Hz), 6.98–7.03 (m, 5H, Ar—H), 7.16 (d, 2H, Ar—H, J = 6.31 Hz), 7.45 (d, 7H, Ar—H, J = 6.3 Hz), 7.94 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 16.28–16.47 (CH₃), 54.28 (CHP), 56.00, 62.50–63.50 (C5′, CH₂), 71.00 (C2′), 76.26 (C3′), 84.50 (C4′), 93.22 (C1′), 119.50, 126.03, 127.50, 128.58–130.06 (phenyl—CH, triazole—CH), 135.50, 139.00 (phenyl—C), 147.50 (triazole—C). ESI‐MS (M+H), m/z calcd. for C₂₅H₃₃N₄O₇P: 532.53, found: 534.10; HRMS (M+K): calcd. for C₂₅H₃₃N₄O₇PK: 571.17184, found: 571.17077.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(dodecylamino)methyl]phosphonate 5i

Yield: 96%; Rf: 0.34; Eluant: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.92 (m, 6H, —OCH₂CH₃, —CH₃), 1.15–1.67 (m, 23H, —CH₂—, —OCH₂CH₃), 7.60 (br s, 1H, NH), 2.33 (m, 2H, —CH₂—NH—), 3.52 (m, 1H, H‐5′A), 3.83–3.91 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 3.99–4.20 (m, 5H, —OCH₂—, H‐2′,3′, CHP), 4.31 (d, 1H, —OH, J = 5.0 Hz), 4.63 (t, 1H, —OH, J = 4.9 Hz), 4.91 (d, 1H, —OH, J = 6.1 Hz), 6.12 (d, 1H, H‐1′, J = 6.4 Hz), 7.28 (d, 2H, Ar—H, J = 8.2 Hz), 7.85 (d, 2H, Ar—H, J = 8.2 Hz), 8.07 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 14.50, 16.00–16.50 (CH₃), 22.65, 27.05, 29.26–40.89 (CH₂), 54.50 (CHP), 61.00–61.88 (C5′, CH₂), 70.85 (C2′), 75.64 (C3′), 86.48 (C4′), 92.80 (C1′), 121.10, 125.44, 128.41 (phenyl—CH, triazole—CH), 133.00–135.00 (phenyl—C), 147.0 (triazole—C). ESI‐MS (M+H), m/z calcd. for C₃₀H₅₁N₄O₇P: 610.72, found: 611.00.

Diethyl [(4‐(1‐(β‐D‐ribofuranos‐1‐yl)‐1,2,3‐triazol‐4‐yl)phenyl)(octadecylamino)methyl]phosphonate 5j

Yield: 97%; Rf: 0.36; Eluant: CH₂Cl₂/MeOH, 95:5 v/v; ¹H NMR (300 MHz, CDCl₃) δ (ppm): 0.78 (t, 3H, —CH₃, J = 6.9 Hz), 1.04–1.50 (m, 38H, —CH₃, —CH₂—), 1.99 (br s, 1H, NH), 2.21 (m, 2H, —CH₂—NH—), 3.70 (m, 1H, H‐5′A), 3.75–4.15 (m, 4H, —OCH₂—, H‐5′B, H‐4′), 4.20–4.46 (m, 5H, —OCH₂—, H‐2′,3′, CHP), 4.51 (d, 1H, —OH, J = 5.0 Hz), 4.87 (t, 1H, —OH, J = 5.2 Hz), 5.29 (d, 1H, —OH, J = 5.3 Hz), 5.99 (d, 1H, H_1′, J = 4.0 Hz), 7.34 (d, 2H, Ar—H, J = 8.4 Hz), 7.67 (d, 2H, Ar—H, J = 8.4 Hz), 8.12 (s, 1H, CH—triazole). ¹³C NMR (75 MHz, CDCl₃) δ (ppm): 14.09, 16.00–16.26 (CH₃), 22.67, 24.78, 27.08, 29.10–29.69, 31.91, 33.95 (CH₂), 54.50 (CHP), 63.00–63.61 (C5′, CH₂), 71.50 (C2′), 76.00 (C3′), 86.00 (C4′), 93.00 (C1′), 121.00, 125.44, 128.41 (phenyl—CH, triazole—CH), 133.20–135.10 (phenyl—C), 147.25 (triazole—C). ESI‐MS (M+H), m/z calcd. for C₃₆H₆₃N₄O₇P: 694.88, found: 696.10; HRMS (M+K): calcd. for C₃₆H₆₃N₄O₇PK: 733.40660, found: 733.40525.

Antiviral activity and cytotoxicity assays

The compounds were evaluated against the following viruses: herpes simplex virus type 1 (HSV‐1) strain KOS, thymidine kinase‐deficient (TK⁻) HSV‐1 KOS strain resistant to ACV (ACV^r), herpes simplex virus type 2 (HSV‐2) strains Lyons and G, varicella‐zoster virus (VZV) strain Oka, TK⁻ VZV strain 07−1, human cytomegalovirus (HCMV) strains AD‐169 and Davis, vaccinia virus Lederle strain, respiratory syncytial virus (RSV) strain Long, vesicular stomatitis virus (VSV), Coxsackie B4, parainfluenza 3, influenza virus A (subtypes H1N1, H3N2), influenza virus B, Reovirus‐1, Sindbis, Reovirus‐1, Punta Toro, human immunodeficiency virus type 1 strain III_B, and human immunodeficiency virus type 2 strain ROD. The antiviral, other than anti‐HIV, assays were based on inhibition of virus‐induced cytopathicity or plaque formation in human embryonic lung (HEL) fibroblasts, African green monkey cells (Vero), human epithelial cells (HeLa), or Madin–Darby canine kidney cells. Confluent cell cultures in microtiter 96‐well plates were inoculated with 100 CCID₅₀ of virus (1 CCID₅₀ being the virus dose to infect 50% of the cell cultures) or with 20 plaque forming units (PFU) (VZV) in the presence of varying concentrations of the test compounds. Viral cytopathicity or plaque formation was recorded as soon as it reached completion in the control virus‐infected cell cultures that were not treated with the test compounds. Antiviral activity was expressed as the EC₅₀ or compound concentration required to reduce virus‐induced cytopathogenicity or viral plaque formation by 50%. The methodology of the anti‐HIV assays was as follows: human CEM (∼3 × 10⁵ cells/mL) were infected with 100 CCID₅₀ of HIV‐1(IIIB) or HIV‐2(ROD)/mL and seeded in 200‐μL‐wells of a microtiter plate containing appropriate dilutions of the test compounds. After 4 days of incubation at 37°C, HIV‐induced CEM giant cell formation was examined microscopically.

Cytotoxicity of the test compounds was expressed as the minimum cytotoxic concentration (MCC) or the compound concentration that caused a microscopically detectable alteration of cell morphology. Alternatively, the cytostatic concentration was calculated as the CC₅₀, or the compound concentration required reducing cell proliferation by 50% relative to the number of cells in the untreated controls.

This project was supported by Centre National de Recherche Scientifique et Technique project RS/2011/01 (Rabat, Morocco). The authors thank the University of Frankfurt for logistic support and all members of the instrumental laboratory for their help (NMR, Mass analysis). The authors also wish to express their gratitude to Mrs. Leentje Persoons, Mrs. Frieda De Meyer, Mrs. Lies Van den Heurck, and Mrs. Lizette van Berckelaer for excellent technical assistance. The biological part of this work was supported by the KU Leuven (GOA 10/014).

The authors have declared no conflicts of interest.

Dedication

This paper is dedicated to John A. (Jack) Secrist III (University of Alabama) on the occasion of his retirement, in memory of the fruitful scientific collaboration, and for his large contributions to medicinal chemistry.

Supporting information

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Supporting Data