Chemical stability of 4'-azidocytidine and its prodrug balapiravir.
BACKGROUND
R1479, a 4'-azidocytidine nucleoside analog, was developed for the treatment of Hepatitis C virus infection. Balapiravir (R1626) is the tri-isobutyrate ester prodrug of R1479 under clinical development to improve exposure of R1479 upon oral administration.


OBJECTIVE
The chemical stability and the rate of azide release of R1479 and balapiravir were studied.


METHODS
R1479 and balapiravir solutions were prepared at different pH values and stored at various temperatures. An ion pair high-performance liquid chromatography (HPLC) method with gradient elution was employed to analyze the prodrug, parent, and degradation products. Azide was measured using a reversed phase HPLC method with UV detection after formation of the 3,5-dinitrobenzoyl azide derivative with 3,5-dinitrobenzoyl chloride. The data were analyzed using initial rate and conventional first-order kinetic methods.


RESULTS
R1479 degrades to cytosine and azide in aqueous solutions, whereas balapiravir mainly degrades to R1479 and mono- and diesters of R1479. The rates of azide release from R1479 and balapiravir were generally comparable with the corresponding amount formed of cytosine.


CONCLUSIONS
Azide release is pH dependent and is faster in acidic solutions than in neutral solutions. The amount of azide released is significantly less from balapiravir than that from R1479, suggesting a potential advantage of the prodrug over the parent drug.
Li
Fujun
F
XenoPort, Inc., Santa Clara, CA 95051, USA. fujun_li@yahoo.com
Wu
Xiaoyang
X
Hadig
Xu
X
Huang
Sujuan
S
Hong
Lei
L
Tran
Tony
T
Brandl
Michael
M
Alfredson
Tom
T
D000998:Antiviral Agents / Q000737:chemistry*; D001386:Azides / Q000737:chemistry; D055598:Chemical Phenomena; D003562:Cytidine / Q000031:analogs & derivatives* / Q000737:chemistry; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D009705:Nucleosides / Q000737:chemistry*; D011355:Prodrugs / Q000737:chemistry*
D000998:Antiviral Agents; D001386:Azides; D009705:Nucleosides; D011355:Prodrugs; D003562:Cytidine; C508950:4'-azidocytidine; C530825:balapiravir