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Ashavina, O. Yu.; Флехтер, О. Б.; Галин, Ф. З.; Kabal'nova, N. N.; Балтина, Л. А.; Толстиков, Г. А.

doi:10.1023/a:1024826316939

Cited by 10 publications

(1 citation statement)

References 6 publications

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“…Compound II was obtained in 89% yield by reaction of betulin with excess trifluoroacetic anhydride (1 : 16) in carbon tetrachloride at 0 to 10°C (Scheme 1). Bis-trifluoroacetate II was isolated previously [2] as a mixture with 28-O-trifluoroacetate in the oxidation of betulin with dimethyl sulfoxide activated by trifluoroacetic anhydride.…”

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Betulin 3,28-Bis-O-trifluoroacetate: Synthesis and Molecular Structure

et al. 2010

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The reaction of betulin with excess trifluoroacetic anhydride gave the corresponding 3,28-bis-Otrifluoroacetate whose molecular structure as a slightly bent "stairway" was determined by X-ray analysis.Betulin (I) is a lupane triterpenoid possessing high biological activity (antiphlogistic, choleretic, antiviral, antitumor, immune modulating, etc.) [1]. The main natural source of betulin is birch bark, where its concentration ranges from 10 to 35%. The ease of isolation and purification of betulin determines sharply increased interest in the synthesis of various its derivatives. Esterification of betulin whose molecule possesses two hydroxy groups gave a number of O-acyl derivatives, some of which were found to be promising as anti-HIV agents [1].In the present work we synthesized betulin 3,28-bis-O-trifluoroacetate (II), taking into account that perfluorocarboxylic acid esters are known to exhibit stronger and more diverse biological activity than their fluorine-free analogs. Compound II was obtained in 89% yield by reaction of betulin with excess trifluoroacetic anhydride (1 : 16) in carbon tetrachloride at 0 to 10°C (Scheme 1). Bis-trifluoroacetate II was isolated previously [2] as a mixture with 28-O-trifluoroacetate in the oxidation of betulin with dimethyl sulfoxide activated by trifluoroacetic anhydride.Diester II is an almost colorless crystalline substance, which is readily soluble in chloroform, methylene chloride, and acetone, poorly soluble in ethyl acetate, and even more poorly soluble in alcohol. The structure of compound II was confirmed by the IR and 1 H and 19 F NMR spectra and X-ray analysis. The IR spectrum of II lacked absorption at about 3446 cm -1 , which is typical of initial diol I, but contained a strong ester carbonyl absorption band (1792 cm -1 ); also, absorption bands due to stretching vibrations of C=C (1640 cm -1 ) and C-F bonds (1220 cm -1 ) were observed. Compound II displayed in the 19 F NMR spectrum two signals with equal intensities at δ F -76.08 and -76.49 ppm, which confirmed the presence of two trifluoroacetoxy groups on C 3 and C 28 . In the 1 H NMR spectrum of II protons in the CH 2 O group resonated as

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confidence: 99%