Asymmetric synthesis of amino-substituted apio dideoxynucleosides as potential anti-HBV agent

Abstract

Apio dideoxynucleosides는 3TC와 같은 nonclassical nucleosides에 속하는 물질로 항바이러스 효과가 있는 것으로 보고되었다. Apio dideoxynucleosides 중 LJ-45는 라세미체로 강한 항 HBV (Hepatitis B Virus) 활성을 나타내었다. 대부분의 약물의 경우, 약효는 라세미체 중 하나의 enantiomer에 의존하고 다른 enantiomer는 주로 독성 등 부작용의 원인이 되므로 LJ-45의 enantiomer들을 각각 합성하여 이들의 항바이러스 작용 및 독성을 비교하고자 실험에 착수하였다. L-serine methylester로부터, Seebach's chemistry를 이용하여 입체선택적으로 중요중간체인 amino sugar acetates (17과 23)를 합성하고 이들을 Mitsunobu 반응을 이용하여 핵산 염기와 축합함으로써 (2R,4R)- and (2S,4S)-LJ-45체를 합성할 수 있었다. 이들 (2R,4R)- LJ-45는 항 HBV효과는 없는 것으로 나타났다. 따라서 다른 enantiomer인 (2S,4S)-LJ-45체에 항 HBV 활성이 있을 것으로 사료되어 현재 (2S,4S)-LJ-45체의 활성을 측정 중에 있다.;Apio dideoxynucleosides in which 4'-hydroxymethyl group moves to C3' position exhibit interesting biological activity like anti-HIV activity. Recently, we have reported the synthesis of racemic amino and azido substituted apio dideoxynucleosides as potential antiviral agents, among which adenine derivative, (±)-LJ-45 was found to be active against hepatitis B virus (HBV). Since biological activity of racemic mixture generally resides in one enantiomer, it was of interest to synthesize each enantiomeric pure form of (±)-LJ-45 and to find out which enantiomer is responsible for anti-HBV activity of (±)-LJ-45. For the synthesis of enantiomeric pure stereoisomer, we utilized Seebach's chemistry to fix the stereochemistry of C3' position. Two nucleosides, (2R,4R)-LJ-45 and (2S,4S)-LJ-45, were synthesized, starting from chiral amino acid, (-)-L-serine methyl ester via oxazolidine carboxylate 6 as a key chiral intermediate. Ozonolysis of 16 and 22 gave the amino apio sugar moiety (17 and 23), respectively. Lact ols (17 and 23) were directly condensed with 6-chloropurine under the standard Mitsunobu conditions to give amino substituted apio dideoxynucleosides (19 and 24), respectively. Aminolysis and deprotection of 19 and 24 gave (2R,4R)-LJ-45 (20a) and (2S,4S)-LJ-45 (26a), respectively. Anti-HBV activity and cytotoxicity of the final nucleosides 20a and 20b were determined in 2.2.15 cells, but both compounds exhibited neither significant anti-HBV activity nor cytotoxicity up to 100 μM. Since biological activity of racemic mixture generally resides in one enantiomer, anti-HBV activity of LJ-45 may reside in (2S,4S)-LJ-45. Further biological evaluation of (2S,4S)-LJ-45 against HBV is in progress in our laboratory.