Synthesis of Novel Triazolo Cyclobutane Nucleoside Analogs
Thi Thu Thuy Tran,†,* Ngoc Thang Ngo,†Thi Ha Dinh,†Giang Vo-Thanh,‡and Stéphanie Legoupy§
†Institute of Natural Products Chemistry, Vietnam Academy of Science and Technology, Hanoi, Vietnam.
*E-mail: thuytran.inpc@gmail.com
‡Equipe de Catalyse Moléculaire-ICMMO, Bât 420 Université Paris-Sud 11, 91405 Orsay Cedex, France
§LUNAM Université, Université d'Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 49045 ANGERS cedex, France
Received October 3, 2014, Accepted January 10, 2015, Published online April 24, 2015
Synthesis of triazolo-cyclobutane nucleosides analogs is reported. These molecules have been obtained by a short and efficient sequence involving a click azide-alkyne cycloaddition following bycis-hydroxylation in the key step.
Keywords: Nucleoside analogs, Click chemistry,cis-Dihydroxylation, Triazolo-cyclobutane
Introduction
Nucleoside analogs have interesting biological activities espe- cially as antiviral or anticancer agents. Besides modification of the ribosyl ring by various five-membered carbasugars,1atten- tion has been directed toward carbocyclic derivatives such as abacavir,2carbovir,3entecavir,4cyclobut-A, and cyclobut-G5 (Figure 1). However, as ribavirin6was reported as therapeutic agent in HCV infection, synthesis of various triazolo- nucleoside analogs have been reported.7
In course of our research program toward nucleoside ana- logs, we have already prepared cyclobutene analogs of carbo- vir 1,8compounds 2with a methylene spacer between the carbocycle and the heterocycle,9nucleosides analogs with a methylene unit103and4, and mono- and polyhydroxylated analogs116and7(Figure 2). We then planned to prepare tri- hydroxylated nucleoside analogs bearing a 1,2,3-triazole moi- etyIandIIvia click azide-alkyne cycloaddition12following bycis-dihydroxylation.
Experimental
Commercially available reagents and solvents were purified and dried, when necessary, by standard methods just prior to use. NMR spectra were recorded on a Bruker AV500 (Rheinstetten, Germany) spectrometer at 500 and 125 MHz for1H and13C, respectively, with TMS as internal standard.
EI-MS spectra were recorded on a LC/MSD Agilent Series 1100 (Santa Clara, CA, USA) instrument. HR-EIS-MS spectra were recorded on a microTOF-QII 10027 (Bruker Daltonics, Bremen, Germany). Elemental analyses were performed at CNRS ISCN, Gif sur Yvette. The optical rotation was deter- mined with a Perkin-Elmer (Waltham, MA, USA) automatic
HO N
N N
N NH2 HO
N N NH
N NH2
HN O
Cyclobut-A, B = Adenine Cyclobut-G, B = Guanine
Abacavir Carbovir
HO
HO B
HO N
N NH
N NH2
O
Entecavir OH
HO N
HO OH N N
NH2 O
Ribavirin
Figure 1.Carbocyclic nucleoside analogs.
HO NN N
R HO NN N
R OH
HO I HO II OH
B
HO HO B HO B B OH
B = adenine or thymine
B = various bases B = adenine
or thymine
HO B
OH
HO B
HO OH
HO B
HO OH
B = adenine
or thymine B = adenine or thymine
1 2 3 4 5
6 7
B = adenine or thymine B = adenine
or thymine
Figure 2.Cyclobutene and cyclobutane nucleoside analogs.
polarimeter. Melting points were recorded on a Buchi B-545 (Switzerland) apparatus and uncorrected.
((1S,4R)-4-((tert-Butyldiphenylsilyloxy)methyl-2)-cyclo- butenyl)methyl methane-sulfonate (10).To a cold solution (0C) of alcohol 9(10 g, 28.4 mmol) and methanesulfonyl chloride (4.39 g, 38.3 mmol) in CH2Cl2(20 mL) was added slowly triethylamine (5.7 g, 56.4 mmol) under argon. The resulting mixture was stirred at rt for 1 h. Water (3 mL) was added and the aqueous layer was extracted with EtOAc (3 × 15 mL). The combined organic phase was dried over Na2SO4
and evaporated to dryness. The residue was purified by column chromatography on silica gel (n-hexane/ethyl acetate 4:1) to yield10(8.3 g, 85%) as a colorless oil.1H NMR (500 MHz, CDCl3) δ7.66 (dd, 4H, J= 6.0 and 2.0 Hz), 7.44–7.38 (m, 6H), 6.18 (d, 1H,J= 2.5 Hz), 6.10 (d, 1H, J= 2.5 Hz), 4.57 (dd, 1H,J= 9.5 and 6.5 Hz), 4.38 (dd, 1H,J= 9.5 and 8.0 Hz), 3.82 (dd, 1H,J= 11.5 and 6.0 Hz), 3.75 (dd, 1H,J= 11.5 and 8.0 Hz), 3.84–3.30 (m, 1H), 3.23–3.20 (m, 1H), 2.90 (s, 3H), 1.05 (s, 9H).13C NMR (125 MHz, CDCl3)δ139.0, 137.1, 135.6 (4C), 133.5, 133.3, 129.8, 129.7, 127.7 (4C), 70.8, 63.4, 47.5, 44.4, 37.2, 26.9 (3C), 19.2. Anal. calcd. for C23H30SiSO4: C, 64.15, H, 7.02, S, 7.49. Found C, 64.11, H, 7.05, S, 7.43.
(((1R,4S)-4-(Azidomethyl)cyclobut-2-enyl)methoxy) (tert- butyl)diphenylsilane (11).To a solution of mesylate10(8.3 g, 24.4 mmol) in anhydrous DMF (50 mL) was added sodium azide (6.3 g, 97.6 mmol) under argon atmosphere. The reac- tion mixture was then stirred at 55C for 12 h. After cooling to room temperature, ice water (100 mL) was added. The aque- ous layer was extracted with EtOAc (4 × 70 mL). The com- bined organic layers were dried over Na2SO4 and concentrated under reduced pressure. Purification of the crude product by column chromatography on silica gel (n-hexane/
ethyl acetate 95:5) afforded azide11(7.6 g, 82%) as colorless oil. 1H NMR (500 MHz, CDCl3) δ 7.68–7.66 (m, 4H), 7.46–7.38 (m, 6H), 6.22 (d, 1H, J= 2.5 Hz), 6.08 (d, 1H, J= 2.5 Hz), 3.83–3.75 (m, 2H), 3.62 (dd, 1H, J= 12.0 and 6.0 Hz), 3.41 (dd, 1H, J= 12.0 and 8.5 Hz), 3.23–3.17 (m, 2H), 1.05 (s, 9H). 13C NMR (125 MHz, CDCl3) δ 138.5, 138.4, 135.6 (4C), 133.7, 133.6, 129.7 (2C), 127.7 (4C), 63.6, 52.0, 48.0, 45.0, 26.9 (3C), 19.2. MSm/z= 399 (M + Na)+. Anal. calcd. for C22H27SiN3O: C, 69.98, H, 7.21, N, 11.13. Found C, 69.75, H, 7.25, N, 10.82.
General Procedure for the Azide-Alkyne Huisgen Cycloaddtion. To a solution of azide11(0.3 g, 0.79 mmol) and selected alkyne (1.2 eq) in tBuOH (2 mL) were added sodium ascorbate 200 mol% (0.32 g, 1.58 mmol, in 1 mL H2O) and 20 mol% CuSO4.5H2O (40.5 mg, 0.16 mmol, in 1 mL H2O) under argon atmosphere. The reaction mixture was stirred overnight at room temperature and then saturated NH4OH solution (5 mL) was added. The mixture was extracted with ethyl acetate (3 × 15 mL). The combined organic layers were dried over Na2SO4 and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (n-hexane/EtOAc) to afford the 1,2,3-triazolocyclobutene.
4-(((tert-Butyldiphenylsilyl)oxy)methyl)-1-(((1S,4R)-4- (((tert-butyldiphenylsilyl)oxy)methyl) cyclobut-2-en-1-yl) methyl)-1H-1,2,3-triazole (12). Yield: 97%. White solid, mp 97–98C.1H NMR (500 MHz, CDCl3)δ7.70–7.66 (m, 8H), 7.46–7.37 (m, 12H), 7.33 (s, 1H), 6.06 (2d overlap, 2H,J= 2.5 Hz), 4.89 (s, 2H), 4.77 (dd, 1H,J= 13.5 and 5.0 Hz), 4.42 (dd, 1H,J= 13.5 and 10.5 Hz), 3.80 (dd, 1H,J= 11.5 and 5.5 Hz), 3.78 (dd, 1H, J= 11.5 and 8.5 Hz), 3.46–3.43 (m, 1H), 3.27–3.26 (m, 1H), 1.09 (s, 18H).13C NMR (125 MHz, CDCl3)δ148.1, 138.4, 138.2, 135.6 (2C), 135.5 (2C), 133.4, 133.2, 129.8 (2C), 127.7 (4C), 121.6, 63.4, 58.7, 51.0, 47.5, 45.5, 26.9 (3C), 26.8 (3C), 19.24, 19.22. HRMS: C41H49N3O2Si2 calcd. for [M + H]+: 672.3436, found: 672.3441.
Benzyl 1-(((1S,4R)-4-(((tert-butyldiphenylsilyl)oxy) methyl)cyclobut-2-en-1-yl) methyl)-1H-1,2,3-triazole-4- carboxylate (13). Yield: 95%. White solid, mp 63–64C .1H NMR (500 MHz, CDCl3)δ8.05 (s, 1H), 7.65 (dd,J= 9.0 and 3.5 Hz, 4H), 7.50–7.31 (m, 11H), 6.07 (m, 2H), 5.40 (s, 2H), 4.85 (dd, 1H, J= 14.0 and 6.0 Hz), 4.51 (dd, 1H, J= 14.0 and 10.5 Hz), 3.87 (dd, 1H,J= 11.0 and 5.0 Hz), 3.75 (dd, 1H, J= 11.0 and 8.5 Hz), 3.48 (dt, 1H, J= 10.0 and 5.0 Hz), 3.25 (dt, 1H,J= 10.0 and 5.0 Hz), 1.07 (s, 9H). 13C NMR (125 MHz, CDCl3) δ 160.6, 139.9, 138.6, 137.7, 135.6 (2C), 135.5 (2C), 133.3, 133.2, 129.9, 129.8, 128.6 (3C), 128.5 (2C), 128.4, 127.80 (4C), 127.5, 66.8, 63.3, 51.4, 47.6, 45.3, 26.9 (3C), 19.2. HRMS: C32H35N3O3Si calcd. for [M + H]+: 538.2520, found: 538.2525.
1-(((1S,4R)-4-(((tert-Butyldiphenylsilyl)oxy)methyl cyclobut-2-enyl)methyl)-4-(3-(trifluoromethyl)phenyl)-1H- 1,2,3-triazole (14).Yield: 98%. Colorless oil.1H NMR (500 MHz, CDCl3)δ7.79 (s, 1H), 7.68–7.66 (m, 5H), 7.59–7.53 (m, 2H), 7.46–7.43 (m, 2H), 7.41–7.38 (m, 5H), 6.14 (d, 1H, J= 2.5 Hz), 6.10 (d, 1H,J= 2.5 Hz), 4.86 (dd, 1H,J= 13.5 and 6.0 Hz), 4.55 (dd, 1H, J= 13.5 and 10.0 Hz), 3.90 (dd, 1H,J= 11.0 and 5.0 Hz), 3.80 (dd, 1H,J= 11.0 and 8.0 Hz), 3.57–3.53 (m, 1H), 3.30–3.27 (m, 1H), 1.05 (s, 9H). 13C NMR (125 MHz, CDCl3)δ146.3, 138.5, 138.0, 135.6 (2C), 135.5 (2C), 133.4, 133.2, 131.6, 129.9, 129.8, 129.3, 128.9, 127.8 (4C), 125.1, 124.6, 123.0, 122.5, 120.1, 63.4, 51.2, 47.6, 45.5, 26.9 (3C), 19.3. HRMS: C31H32N3OF3Si calcd.
for [M + H]+: 548.2340, found: 548.2345.
1-(((1S,4R)-4-((tert-Butyldiphenylsilyl)oxy)methyl) cyclobut-2-en-1-yl)methyl)-4-(3,5-difluorophenyl)-1H-1,2,3- triazole (15).Yield: 94%. Colorless oil.1H NMR (500 MHz, CDCl3)δ7.63 (s, 1H); 7.60–7.58 (m, 4H), 7.37–7.35 (m, 2H), 7.33–7.31 (m, 4H), 7.25–7.23 (m, 2H), 6.70–6.67 (m, 1H), 6.05 (d, 1H, J= 2.5 Hz), 6.02 (d, 1H,J= 2.5 Hz), 4.77 (dd, 1H, J= 13.5 and 6.0 Hz), 4.46 (dd, 1H, J= 13.5 and 10.0 Hz), 3.82 (dd, 1H, J= 11.0 and 5.0 Hz), 3.73 (dd, 1H, J= 11.0 and 8.5 Hz), 3.47–3.45 (m, 1H), 3.20–3.18 (m, 1H), 1.01 (s, 9H).13C NMR (125 MHz, CDCl3)δ164.3 (d,J= 13.0 Hz), 162.4 (d,J= 13.2 Hz), 145.7, 138.5, 137.9, 135.6 (2C), 135.5 (2C), 133.8, 133.3, 133.2, 129.9 (2C), 127.8 (4C), 120.4, 108.5 (d, J= 6.5 Hz), 108.3 (d, J= 6.0 Hz), 103.2 (t, J= 25.0 Hz), 63.4, 51.2, 47.6, 45.5, 26.9 (3C), 1391
19.2. HRMS: C30H31N3OF2Si calcd. for [M + H]+: 516.2277, found: 516.2283.
tert-Butyl-(1-(((1S,4R)-4-((tert-butyldiphenylsily- loxy) methyl)cyclobut-2-enyl)methyl)-1H-1,2,3-triazol-4- yl)methylcarbamate (16). Yield: 82%. White solid, mp 101–102C.1H NMR (500 MHz, CDCl3) δ 7.66–7.64 (m, 4H), 7.51 (s, 1H), 7.46–7.38 (m, 6H), 7.12–7.08 (m, 1H), 6.08 (d, J= 2.5 Hz, 1H), 6.06 (d, J= 2.5 Hz, 1H), 4.78 (dd, J= 14.0 and 6.0 Hz, 1H), 4.45 (dd, J= 14.0 and 10.5 Hz, 1H), 4.39 (m, 2H), 3.86 (dd, J= 11.0 and 5.0 Hz, 1H), 3.76 (dd,J= 11.0 and 8.5 Hz, 1H), 3.45 (ddd,J= 5 Hz, 1H), 3.25 (ddd, J= 5 Hz, 1H), 1.44 (s, 9H), 1.07 (s, 9H). 13C NMR (125 MHz, CDCl3) δ 158.8, 156.9, 138.3, 138.2,135.6, 135.55, 133.4, 133.3, 129.84, 129.82, 127.8, 64.4, 51.1(2C), 47.5, 45.4, 36.1, 28.4, 26.9, 19.2 (2C) . HRMS: C30H40N4O3Si calcd. for [M + H]+: 53.2942, found: 533.2948.
General Procedure for Dihydroxylation of Cyclobutene Nucleoside Analogs Following by Desilylation. 4- MethylmorpholineN-oxide (102 mg, 0.870 mmol) and a 4%
aqueous solution of OsO4(76μL, 3.05 mg, 0.012 mmol) were added to a solution of cyclobutene (0.58 mmol) in a THF:H2O (10:1) mixture (2.5 mL). The reaction mixture was stirred at room temperature for 4 h then 20% NaHSO3 solution (5 mL) was added at 0C. The mixture was extracted with ethyl acetate (5 × 10 mL). The combined organic layers were dried over Na2SO4and concentrated under reduced pressure. The residue containing two isomers was submitted to the deprotec- tion reaction.
To the crude mixture of silylated diols (0.4 mmol) THF (4 mL) was added a solution of TBAF 1 M in THF (800μL). The reaction mixture was stirred at room temperature for 30 min then saturated NH4Cl and ethyl acetate were added.
The organic layer was separated, dried over Na2SO4and con- centrated under reduced pressure. The residue was purified by column chromatography (dichloromethane/methanol 10:1) to successively lead to isomer cis-isomer c then to trans-isomerd.
(1R,2S,3R,4S)-3-(Hydroxymethyl)-4-((4-(hydroxyl- methyl)-1H-1,2,3-triazol-1-yl)methyl) cyclobutane-1,2diol (17c).Yield: 27%. White solid, mp 208–209C.½ α20D + 104 (c 1.450, MeOH). 1H NMR (500 MHz, CD3OD)δ7.96 (s, 1H), 4.77 (dd, J= 14.0 and 9.5 Hz, 1H), 4.68 (s, 2H), 4.67 (dd,J= 14.0 and 5.5 Hz, 1H), 4.39–4.36 (m, 1H), 4.33–4.30 (m, 1H), 3.96–3.88 (m, 2H), 2.91–2.87 (m, 1H), 2.71–2.67 (m, 1H). 13C NMR (125 MHz, CD3OD) δ 148.8, 124.5, 70.5, 69.0, 59.2, 56.5, 47.4, 43.5, 39.9. HRMS: C9H16N3O4,
calcd. for [M + H]+: 230.1135, found: 230.1138.
(1S,2R,3R,4S)-3-(Hydroxymethyl)-4-((4-(hydroxyl methyl)-1H-1,2,3-triazol-1-yl)methyl) cyclobutane-1,2diol (17d). Yield: 33%. White solid, mp 165–166C. ½ α20D −8 (c 2.800, MeOH). 1H NMR (500 MHz, CD3OD)δ7.97 (s, 1H), , 4.69 (s, 2H), 4.68 (dd,J= 14.0 and 7.5 Hz, 1H), 4.58 (dd,J=14.0 and 9.0 Hz, 1H), 4.17 (dd,J= 6.0 and 3.0 Hz, 1H), 4.13 (dd,J= 6.0 Hz, 1H), 3.77 (m, 2H), 2.96–2.91 (m, 1H), 2.47–2.34 (m, 1H). 13C NMR (125 MHz, CD3OD) δ 149.0, 124.2, 70.9, 70.9, 60.7, 56.5, 50.5, 45.2, 44.4. HRMS:
C9H15N3O4Na calcd. for [M + Na]+: 252.0955, found:
252.0957.
Benzyl 1-(((1S,2R,3S,4R)-2,3-dihydroxy-4-(hydroxyl methyl)cyclobutyl)methyl)-1H-1,2,3-triazole-4-carbo-xylate (18c). Yield: 28%. White solid, mp 216–217C.½ α20D + 19 (c 1.200, MeOH). 1H NMR (500 MHz, CD3OD)δ8.55 (s, 1H), 7.47 (d, J= 7.0 Hz, 2H), 7.40–7.35 (m, 3H), 5.38 (s, 2H), 4.85 (dd,J= 14.0 and 9.0 Hz, 1H), 4.73 (dd,J= 14.0 and 5.5 Hz, 1H), 4.37–4.34 (m, 1H), 4.30–4.28 (m, 1H), 3.91 (d, J= 7.0 Hz, 2H), 2.94–2.90 (m, 1H), 2.69–2.66 (m, 1H).13C NMR (125 MHz, CD3OD) δ161.9, 140.2, 137.2, 130.2, 129.6 (2C), 129.5 (2C), 129.4, 70.1, 69.2, 67.7, 59.2, 48.0, 43.1, 39.9. HRMS: C16H20N3O5calcd. for [M + H]+: 334.1397, found: 334.1396.
Benzyl 1-(((1S,2S,3R,4R)-2,3-dihydroxy-4-(hydroxyl- methyl)cyclobutyl)methyl)-1H-1,2,3-triazole-4carboxy-late (18d).Yield: 52%. White solid, mp 171–172C.½ α20D −123 (c 2.300, MeOH). 1H NMR (500 MHz, CD3OD) δ8.60 (s, 1H), 7.47 (d, J= 7.0 Hz, 2H), 7.40–7.33 (m, 3H), 5.39 (s, 2H), 4.74 (dd, J= 14.0 and 7.5 Hz, 1H), 4.65 (dd, J= 14.0 and 9.0 Hz, 1H), 4.15–4.11 (m, 2H), 3.79–3.72 (m, 2H), 3.00–2.93 (m, 1H), 2.41–2.37 (m, 1H).13C NMR (125 MHz, CD3OD) δ 161.8, 140.4, 137.2, 129.8, 129.6 (2C), 129.5 (2C), 129.4, 70.9 (2C), 67.7, 60.7, 51.0, 45.1, 44.3. HRMS:
C16H20N3O5calcd. for [M + H]+: 334.1397, found: 334.1399.
(1R,2S,3R,4S)-3-(Hydroxymethyl)-4-((4-(3-(trifluoro- methyl)phenyl)-1H-1,2,3-triazol-1-yl)methyl)cyclo butane- 1,2-diol (19c). Yield: 34%. White solid, mp 222–223C.
α
½ 20D + 22 (c 0.750, MeOH). 1H NMR (500 MHz, DMSO d6)δ8.67 (s, 1H), 8.14 (m, 2H), 7.68 (m, 2H), 5.10 (d,J= 5.0 Hz, 1H), 4.85 (d,J= 5.0 Hz, 1H), 4.68 (dd,J= 14.0 and 9.0 Hz, 1H), 4.61 (dd, J= 14.0 and 6.0 Hz, 1H), 4.44 (dd, J= 5.0 and 4.5 Hz, 1H), 4.20 (m, 2H), 3.74–3.69 (m, 1H), 3.69–3.64 (m, 1H), 2.86–2.79 (m, 1H), 2.54–2.47 (m, 1H).
13C NMR (125 MHz, DMSO d6) δ 144.5, 132.0, 130.1, 129.6 (q, J= 32.0 Hz), 128.8, 125.2, 124.1, 122.4, 121.3, 68.4, 67.7, 57.3, 46.3, 41.6, 38.4. HRMS: C15H17F3N3O3
calcd. for [M + H]+: 344.1217, found: 344.1208.
(1S,2R,3R,4S)-3-(Hydroxymethyl)-4-((4-(3-(trifluoro- methyl)phenyl)-1H-1,2,3-triazol-1-yl)methyl)cyclo butane- 1,2-diol (19d). Yield: 41%. White solid, mp 178–179C.
α
½ 20D −28 (c 1.300, MeOH). 1H NMR (500 MHz, CD3OD) δ 8.51 (s, 1H), 8.16 (s, 1H), 8.09 (dd, J= 4.0 and 3.0 Hz, 1H), 7.65 (m, 2H), 4.76 (dd,J= 14.0 and 7.5 Hz, 1H), 4.66 (dd,J= 14.0 and 9.0 Hz, 1H), 4.20–4.16 (m, 2H), 3.84–3.77 (m, 2H), 3.05–2.99 (m, 1H), 2.46–2.42 (m, 1H).13C NMR (125 MHz, CD3OD) δ 147.3, 133.0, 132.3 (q, J 32.2 Hz), 130.8, 130.1, 125.6 (d,J3.7 Hz), 124.5, 123.2 (d,J3.7 Hz), 123.0, 71.0, 70.9, 60.7, 50.8, 45.2, 44.4. HRMS:
C15H17F3N3O3 calcd. for [M + H]+: 344.1217, found:
344.1211.
(1S,2R,3S,4R)-3-((4-(3,5-Difluorophenyl)-1H-1,2,3-tria- zol-1-yl)methyl)-4-(hydroxymethyl) cyclobutane-1,2-diol (20c). Yield: 31%. White solid, mp 219–220C. ½ α20D + 95 (c 2.300, MeOH). 1H NMR (500 MHz, CD3OD)δ8.43 (s,
1H), 7.47–7.42 (m, 2H), 6.95–6.90 (m, 1H), 4.84 (dd,J= 14.0 and 9.5 Hz, 1H), 4.73 (dd,J= 14.0 and 6.0 Hz, 1H), 4.39 (ddd, J= 7.0, 5.5 and 1.5 Hz, 1H), 4.34 (ddd,J= 6.0 and 2.0 Hz, 1H), 4.98–3.92 (m, 2H), 2.99–2.94 (m, 1H), 2.75–2.70 (m, 1H). 13C NMR (125 MHz, CD3OD) δ 165.9 (d, J= 13.0 Hz), 164.0 (d, J= 13.5 Hz), 146.4, 135.5 (t, J= 10 Hz), 123.8, 109.4 (d, J= 6.6 Hz), 109.2 (d,J= 6.6 Hz), 103.9 (t, J= 26.0 Hz), 70.4, 69.1, 59.2, 47.8, 43.4, 40.0. HRMS:
C14H16F2N3O3 calcd. for [M + H]+: 312.1154, found:
312.1153.
(1R,2S,3S,4R)-3-((4-(3,5-Difluorophenyl)-1H-1,2,3-tria- zol-1-yl)methyl)-4-(hydroxymethyl) cyclobutane-1,2-diol (20d). Yield: 39%. White solid, mp 182–183C. ½ α20D −11 (c 1.650, MeOH). 1H NMR (500 MHz, CD3OD)δ8.46 (s, 1H), 7.47–7.42 (m, 2H), 6.95–6.90 (dddd,J= 9.0 and 2.0 Hz, 1H), 4.74 (dd, J= 14.0 and 7.0 Hz, 1H), 4.65 (dd, J= 14.0 and 9.0 Hz, 1H), 4.20–4.16 (m, 2H), 3.84–3.76 (m, 2H), 3.02–2.97 (m, 1H), 2.46–2.41 (m, 1H). 13C NMR (125 MHz, CD3OD) δ165.9 (d,J= 13.3 Hz), 163.9 (d, J= 13.3 Hz), 146.7, 135.4 (t, J= 10 Hz) 123.4, 109.4 (d, J= 6.6 Hz), 109.2 (d, J= 6.6 Hz), 104.0 (t, J= 25.9 Hz), 71.0 70.9, 60.7, 50.8, 45.1, 44.4. HRMS: C14H16F2N3O3 calcd.
for [M + H]+: 312.1154, found: 312.1148.
Results and Discussion
The starting material was the monoacetate8which is available in high enantiomeric excess by an enzymatic acylation as pre- viously described by Huetet al.13Protection of this alcohol as a silyl derivative followed by removal the acetyl group in presence of NH3/MeOH gave the alcohol 9 in good yield (Scheme 1). Treatment of9with methanesulfonyl chloride and triethylamine afforded mesylate10in 85%. Nucleophilic substitution of10with sodium azide at 55C in DMF provided azide11in 82% isolated yield.
Azide11was subjected to azide-alkyne Huisgen cycloaddi- tion reaction with various alkynes. The cycloaddition reaction was carried out under different solvent systems such as EtOH, EtOH:H2O (1:1), MeOH, MeOH:H2O (1:1), propanol, propa- nol:H2O (1:1), BuOH and BuOH:H2O (1:1). The best result was obtained after stirring the reaction mixture overnight at room temperature intBuOH:H2O (1:1) solvent system with Cu(I) (CuSO4.5H2O and sodium ascorbate) as catalyst.
Applying this procedure, we successfully synthesized 1,2,3- triazolocyclobutene 12–16 in good yields (Scheme 2 and Table 1).
The regiochemistry of the azide-alkyne cycloaddition pro- ducts was established by NOESY experiments. Strong NOE
effects have been observed between the proton of triazole's ring and the N-CH2proton, suggesting the 1,4-disubstituted triazole with 1 proton which is close to this CH2 proton (Figure 3).
cis-Hydroxylation of cyclobutene compounds 12–16 by reaction withN-methylmorpholine N-oxide in the presence of osmium tetroxide as catalyst led to a mixture ofcis-aand trans-isomers b (Scheme 3). The subsequent desilylation without purification of the crude mixture provided a mixture of triazolo-cyclobutane nucleoside analogs 17–20c and 17–20d, which were separated by chromatography on silica gel (Table 2). The hydroxylated products of compound 16 could not be separated and purified properly by chromatogra- phy on silica gel.
The structures of triazolo-cyclobutane nucleoside analogs have been unequivocally assigned by NMR experiments.
The phase-sensitive NOESY experiments of trans-isomers dshowed correlations between H-3/H-6 and H-2/H-5. Similar correlations were absent incis-isomersc(Figure 4).
Compounds17–20cand17–20dwere subjected to antimi- crobial evaluation against E.coli,P.aeruginosa,B. subtillis, S. aureus,A. niger,F. oxysporum,S. cerevisiae, andC. albi- can, cytotoxicity in KB cells, VSV, HSV-1 and 2, HIV-1 and 2, and H5N1 virus. No significant activity was observed for antimicrobial and antiviral activity. However, compounds 17d,18d,19c,19d, and20cshowed moderate cytotoxic activ- ity with IC50 of 39.6–52.4μg/mL against KB cell lines (Table 3, an anticancer agent ellipticine was used as positive control).
OH
OAc
OTBDPS
OH
OTBDPS 11 N3
8 9
a,b c OTBDPS
10 OMs
d
85% 82%
>96.8% ee
70%(2steps) (ref 9)
Scheme 1. Reagents and conditions: (a) tBuPh2SiCl, imidazole, DMF; (b) NH3/MeOH; (c) MsCl, Et3N, CH2Cl2; (d) NaN3, DMF, 55C.
TBDPSO NN N
OTBDPS N3
+ R R
11 12-16
CuSO4.5H2O (20 mol%) NaAsc (200 mol%)
tBuOH/H2O 1/1, r.t.,12h
Scheme 2.Click reactions.
Table 1.Click azide-alkyne cycloaddition.
Entry R Product Yield %a
1 TBDPSO CH2 12 97
2 COOBn 13 95
3 m CF3C6H5 14 98
4 F
F
15 94
5 -CH2-N-Boc 16 82
aIsolated yield.
TBDPSO
1N 5
N 4
N
CF3
H 14
Figure 3.NOESY correlation for14.
1393
Conclusion
In summary, several triazolo-nucleoside analogs were synthe- sized by a short route involving the Huisgen 1,3-dipolar cyclo- addition. Compounds17d,18d,19c,19d, and20cshowed moderate cytotoxic activity against KB cell lines.
Acknowledgments. We thank the Vietnam National Foundation for Science and Technology Development (NAFOSTED) for financially supporting under project No.
104.01.91.09.
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Table 3.Cytotoxic activity of triazolo-cyclobutane nucleoside analogs.
C (μg/mL) 17d 18d 19c 19d 20c Ellipticine
100 80.9 67.1 69.5 73.2 65.9 95.4a
20 40.9 36.6 40.9 39.1 30.5 66.8
4 28.0 13.3 16.1 9.4 11.1 15.7
0.8 9.4 11.5 12.9 8.5 4.5 −5.4
IC50 38.5 45.9 39.8 39.6 52.4 1.01
a% inhibition on KB cell lines.
Table 2.Synthesis of triazolo-cyclobutane nucleoside analogs.
Entry Triazole
Ratio a/b
cis- isomerc
trans- isomerd
Yield %a c/d
1 12 45/55 17c 17d 27/33
2 13 35/65 18c 18d 28/52
3 14 45/55 19c 19d 34/41
4 15 44/56 20c 20d 31/39
aIsolated yield.
TBDPSO NN N R
TBDPSO NN N R
TBDPSO NN N R HO OH
OH HO
a
b +
HO NN N
R
HO NN N
R OH HO
HO OH
c
d TBAF +
12-15
OsO4, NMO THF/H2O
Scheme 3.cis-Dihydroxylations and desilylations of12–16.
1 23
HO 4
OH
5
6
HO
N N N
CF3
H H
1 23
H 4
H
5
6
HO
N N N
CF3
OH HO
19c 19d
Figure 4.NOESY correlations for19cand19d.
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