Y. Huang, F. Bennett, A. Buevich et al.
Tetrahedron Letters 72 (2021) 153066
to bis-carbamate 23 was accomplished with cesium carbonate at
room temperature. The silyl ether, ethyl enolether, and tert-butyl
carbamates were cleaved simultaneously in one pot using warm
dilute aqueous HCl in THF over the course of two days, revealing
the desired nucleoside 6 [13].
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
The initial phosphorylation during the metabolic step-wise
transformation of a nucleoside to its NTP can be rate-limiting as
observed with 20-F guanosine analogs, and measurements of cell-
based activity may not accurately reflect the intrinsic potency of
the active NTP metabolite [14]. To ascertain their effectiveness as
potential antiviral agents both nucleosides 5 and 6 were converted
to the corresponding 50-O-triphosphates 24a and 25a [15]. Their
inhibitory activity against wild-type HCV NS5B polymerase was
evaluated along with other relevant nucleoside triphosphates
(Table 1) [16].
Appendix A. Supplementary data
Supplementary data to this article can be found online at
References
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A.; Vacca, J. P. WO2012142075 A1 20121018. (c) Girijavallabhan, V.;
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Y.-H.; Hong, Q.; Liu, Z.; Pan, W.; Pu, H.; Rossman, R.; Truong, Q.; Vibulbhan, B.;
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Nucleosides, Nucleotides Nucleic Acids 2016, 35, 277-294.
A direct comparison of the b-ethynyl 24a with its methyl
counterpart (24c) revealed a modest 3–4 fold boost in potency
in the uridine nucleoside series. This effect was more pronounced
with a hydroxyl group in the C20-
a position (24b vs. 24d) [4]. In
the guanosine example, this effect was reversed, the acetylene
25a being approximately 2-fold less potent than the known
methyl analogue 25b. Importantly, both novel nucleoside triphos-
phates 24a and 25a exhibit comparable potency with the triphos-
phate derived from Sofosbuvir 24e and clearly merit further
consideration.
In summary, we have synthesized biologically relevant nucle-
osides bearing an ethynyl at the C20- b-position and an amino as
the
a-moiety from inexpensive and readily available uridine and
guanosine. Our route highlighted a key synthetic transformation,
in which a tethered aminohydroxylation was employed to pre-
pare a highly functionalized ribose core with diastereospecificity.
To evaluate their potential as anti-HCV agents, the corresponding
50-O-triphosphates were prepared and their inhibitory activity
against wild type NS5B polymerase was measured. While the
ethynyl amino uridine derivative 24a was approximately 3 times
more potent that the C20- b-Me analogue 24c, the introduction of
the ethynyl group into guanosine 25a had the opposite effect.
Ultimately, both triphosphates have IC50’s in the low single digit
lM range, comparable to the metabolite 24e formed on adminis-
tration of Sofosbuvir. Application of this and other studies related
to the nucleosides described in this paper will be presented
elsewhere.
[8] (a) T. J. Donohoe and S. Mesch, in Asymmetric Synthesis II, ed. M. Christmann
and S. Brase, 2012, pp. 17–27.; (b) Donohoe, T.; Bataille, C.J.R; Gattrell, W.;
Kloesges, J.; Rossignol, E.; Org. Lett., 2007, 9, 1725. (c) Donohoe, T.; Johnson, P.;
Pye, R.; Org. Biomol. Chem., 2003, 1, 2025. (d) Donohoe, T.; Callens, C.;
Thompson, A.; Org. Lett., 2009, 11, 2305. (e) Donohoe, T.; Callens, C.;
Thompson, A.; Lacy, A.; Winter, C.; Eur. J. Org. Chem. 2012, 655.
[9] Bennett, F.; Huang, Y.; Wang, L.; Bogen, S. L.; Kerekes, A. D.; Girijavallabhan, V.;
Butora, G.; Truong, Q.; Davies, I.; Weber, A. E. WO2014078463.
Table 1
Activities of the nucleoside triphosphates against NS5B polymerase.
[11] (a) Ohira, S.; Synth. Commun. 1989, 19, 561. (b) Muller, S.; Liepold, B.; Roth, G.
J.; Bestmann, H-J. Synlett., 1996, 521. (c) Roth, G. J.; Liepold, B.; Muller, S. G.;
Bestmann, H-J. Synthesis, 2004, 59.
[12] MS and NMR for Compound 5. 1H NMR (599 MHz, CD3OD): d8.10(d; J = 8.12
Hz; 1H); 5.90 (s; 1H); 5.67 (d; J = 8.11 Hz; 1H); 4.26 (d; J = 8.22 Hz; 1H); 3.93-
3.94 (m; 2H); 3.75 (dd; J = 12.32; 2.93 Hz; 1H); 3.22 (t; J = 8.46 Hz; 1H); 2.92
(s; 1H). 13C NMR (151 MHz, CD3OD): d166.28,152.72,143.95,142.50,136.17,
120.99,108.72,102.23,92.70,84.86,84.48,75.97,61.81,60.75,59.66,59.64,59.64,
59.62,24.93,20.88, 20.87, 14.09, [M+1]=268.27.
[13] MS and NMR for Compound 6. 1H NMR (599 MHz, CD3OD) d 8.16 (s, 1H), 5.93
(s, 1H), 4.53 (d, J = 7.9 Hz, 1H), 4.06 (dt, J = 7.9, 3.2 Hz, 1H), 3.96 (dd, J = 12.4,
2.8 Hz, 1H), 3.82 (dd, J = 12.4, 3.6 Hz, 1H), 2.70 (s, 1H). 13C NMR (151 MHz,
CD3OD) d 159.46, 155.49, 153.02, 138.05, 117.49, 91.70, 84.98, 84.27, 76.01,
75.69, 62.36, 61.46.[M+1]=307.17.
[14] Furman,; P. A., Muramami, E., Niu, C., Lam, A. M., Espiritu, C., Bansal, S., Bao, H.,
Tolstykh, T., Sreuer, H. M., Keilman, M., Zennou, V., Bourne, N., Veselenak, R. L.,
Chang, W., Ross, B. S., Du, J., Otto, M. J., Sofia, M. J. Antiviral Res. 91 2011 120.
[15] General Preparation of Nucleoside 5‘-Triphosphates The preparation 5’-
triphosphates.(24a-c and 25a-b) were carried under contractual agreement
with TriLink biotechnologies, San Diego, CA.and analysed as the
NTP
24a
24b
24c
24d
24e
25a
25b
a
b
IC50
3.2
(lM)
0.09
11
a
0.43
1.1 b,[14]
1.3
triethylammonium salts. Triphosphates 24d and 24e were prepared in
a
similar manner and examined as the dimethylhexylammonium salts and
sodium salts, respectively. For example: A solution of the nucleoside (0.05
mmol) in trimethylphosphate (1 ml) was placed under an atmosphere of
nitrogen. To this solution was added proton sponge (17 mg; 0.08 mmol) and
the resulting mixture was cooled in an ice bath. Phosphoryl trichloride (32 mg;
0.6
a
Prepared and tested as dimethylhexylammonium salts
Prepared and tested as sodium salts.
b
3