46(PA1-4) バイユノシド及び関連甘味配糖体の全合成(ポスター発表の部)

抄録

Sweet taste is one of the fascinating field of organic chemistry on the basis of social requirements to find low calorie and high quality taste. Baiyunoside (1) has been characterized as a sweet taste principle of chinese drug, Bai-Yun-Shen (Phlomis betonicoides), by Tanaka and co-workers along with the minor sweet glycoside named phlomisoside I (2). We have designed a general approach to this class of sweet glycosides in order to develop high quality artificial sweeteners. We have already reported an efficient total synthesis of (±)-baiyunol (4), the aglycon of 1 and 2 by means of selective olefin cyclization using mercury(II) triflate/N,N-dimethylaniline complex. We disclose herein the first total synthesis of baiyunoside (1) from (±)-baiyunol (4) via a novel 2' discriminated glycosidation using 2' free glycosyl halide. This novel glycosidation does not accompanied any oligosaccharide formation and this result suggests that very severe steric bulk exist at the newly formed 2' hydroxyl moiety of 6a. As is the case, 6a was entirely inert against a variety of Koenigs-Knorr type glycosidation in order to introduce the xylose moiety. However, Noyori's glycosidation based on a strong affinity between silicon and fluorine was efficiently applied to our purpose. When trimethylsilyl ether 16 was treated with fluorosugar 15 in toluene in the presence of catalytic amount of trimethylsilyl triflate afforded disaccharide 17 and 18 in 38: 62 ratio and in 58% yield. Deprotection of the latter afforded baiyunoside (1) and identified with natural product in every respects. Therefore, we have established a general way to prepare a wide variety of baiyunoside analogs in order to evaluate the taste.