Synthesis of Hypermodified Nucleosides Related to Phenylalanine Transfer Ribonucleic Acids.

(1)An通过<Phe>1-苄基-7-甲酰基怀伊与由（R）-2-[（R）-7-（甲氧羰基）氨基]-3-（三苯基膦酰基）-丙酸酯，然后甲基化，SO_4氧化，并在吡啶存在下与COCl_2环化缩合。通过裂解环状碳酸酯，再经NaBH_4还原和催化氢解，方便地制备了手性碱光学纯度测定所需的（R ~*，R ~*）-β-羟基丁酸丁及其非对映体。因此，[R-（R*，S*）]-和[S-（R*，R*）-β-羟基丁酸酯的样品显示为光学纯的。（2）核苷水平的合成从3-[2，3，5-三-O-（叔丁基二甲基硅基）-beta-D-呋喃核糖基] Y的Vilsmeier反应开始，经过与（R）-2-[（甲氧羰基）-氨基]-3-（三苯基膦酰基）丙酸酯的Wittig反应、与三甲基硅基重氮甲烷的甲基化、0 s 04氧化、与三光气的环化缩合和催化氢解。所得非对映异构体混合物的色谱分离和随后的脱保护首次得到两种所需的核苷。(3)it已经揭示，在0.25 ℃下，1-苄基-4-甲基-4，9-二氢-1H-咪唑并[1 ; 2-α]嘌呤-9-酮在0.1M MeONa-MeOH中的异构化速率随着7-取代基吸电子性质的增加而增加，并且9-位上的羰基与7-取代基之间的分子内氢键进一步促进了反应性。

(1)An improved synthesis of the key intermediates for the synthesis of [R-(R*, S*)]- and [S-(R*, R*)]-beta-hydroxywybutines, the most probable structures for the minor base from rat liver tRNA^<Phe>, has been achieved by the Wittig reaction between 1-benzyl-7-formylwye and the phosphorane derived from (R)- 2-[(methoxycarbonyl)amino]-3-(triphenylphosphonio)- propanoate, followed by methylation, 0S0_4 oxidation, and cyclo-condensation with COCl_2 in the presence of pyridine. (R*, R*)-beta-Hydroxywybutine and its diastereomer, which were required for the determination of the optical purity of the chiral bases by means of chiral HPLC, were conveniently prepared through pyrolysis of the cyclic carbonate followed by NaBH_4 reduction and catalytic hydrogenolysis. The samples of [R-(R*, S*)]- and [S-(R*, R*)-beta-hydroxywybutines were thus shown to be optically pure.(2)The synthesis at the nucleoside level started with the Vilsmeier reaction of 3-[2,3,5-tris-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]wye and proceeded through the Wittig reaction with (R)-2-[(methoxycarbonyl)-amino]-3-(triphenylphosphonio)propanoate, methylation with trimethyl-silyldiazomethane, 0s04 oxidation, cyclocondensation with triphosgene, and catalytic hydrogenolysis. Chromatographic separation of the resulting diastereomeric mixture and subsequent deprotection afforded the two desired nucleosides for the first time.(3)it has been revealed that the rate of isomerization of l-benzyl-4-methyl-4,9-dihydro- 1H-imidazo[1 ; 2-alpha]purin-9-ones in 0.1 M MeONa-MeOH at .25*C increases with increasing electron-withdrawing nature of the 7-substituent and that the reactivity is further promoted by the intramolecular hydrogen bond between the carbonyl group at the 9-position and the 7-substituent.