Reaction of ethyl (R)-oxiranecarboxylate (2a) with various nucleobases (adenine, 6-chloropurine, thymine, cytosine, N6-benzoyladenine, 4-methoxy-5-methylpyrimidin-2(1H)-one and 4-methoxypyrimidin-2(1H)-one) afforded ethyl 3-substituted-2-hydroxypropanoates 4-10. Enantioselectivity of this reaction is dependent on the type of the base: 6-chloropurine, N6-benzoyladenine, 4-methoxy-5-methylpyrimidin-2(1H)-one, thymine and cytosine gave optically pure R enantiomers. In other cases, partial or complete racemization occurred. Optically pure ethyl (R)-3-(6-chloropurin-9-yl)-2-hydroxypropanoate (5a) was hydrolyzed to give (R)-3-(6-chloropurin-9-yl)-2-hydroxypropanoic acid (11). Reactions of 11 with various primary or secondary amines led to N6-substituted (R)-3-(adenin-9-yl)-2-hydroxypropanoic acids 14-19. Enantiomeric purity was determined from 1H NMR spectra measured in the presence of (-)-(R)-1-(9-anthryl)-2,2,2-trifluoroethan-1-ol.
乙基(R)-环氧丙酸乙酯(2a)与各种核碱基(腺嘌呤、6-氯嘌呤、胸腺嘧啶、胞嘧啶、N6-苯甲酰腺嘌呤、4-甲氧基-5-甲基嘧啶-2(1H)-酮和4-甲氧基嘧啶-2(1H)-酮)反应生成乙基3-取代-2-羟基丙酸酯4-10。该反应的对映选择性取决于碱基的类型:6-氯嘌呤、N6-苯甲酰腺嘌呤、4-甲氧基-5-甲基嘧啶-2(1H)-酮、胸腺嘧啶和胞嘧啶生成光学纯R对映异构体。在其他情况下,部分或完全消旋发生。光学纯乙基(R)-3-(6-氯嘌呤-9-基)-2-羟基丙酸酯(5a)水解得到(R)-3-(6-氯嘌呤-9-基)-2-羟基丙酸(11)。11与各种一级或二级胺的反应导致N6-取代(R)-3-(腺嘌呤-9-基)-2-羟基丙酸14-19。对映纯度是通过在(-)-(R)-1-(9-蒽基)-2,2,2-三氟乙醇存在下测定的1H NMR谱来确定的。