The reactions of beta- and alpha-pyranose peracetates with PCl5, and utilization of the products to construct sarsasapogenin glycosides.

The reactions of beta- and alpha-pyranose peracetates with PCl5 gave products regioselectively chlorinated. The reactions of 1,2,3,4,6-penta-O-acetyl-beta-D-glucopyranose (5) and -beta-D-galactopyranose (6) with PCl5 in CCl4 and that of methyl 2,3,4-tri-O-acetyl-beta-D-glucuronatopyranose (7) with PCl5 in toluene gave 2-O-trichloroacetyl-beta-D-pyranosyl chlorides 4, 12 and 14, respectively, as major products, and alpha-D-pyranosyl chlorides 11, 13 and 15, respectively, as minor products. On the other hand, the reactions of compounds 8 and 9 which were alpha-anomers of 5 and 6, respectively, with PCl5 gave as major products transformed acetyl groups at C-6 to -C(Cl) = CCl2 or -C(Cl)2-CCl3 group (16 and 17 from 8 and 18 from 9). The same reaction of 10, which was alpha-anomer of 7, gave alpha-chloride 15 as a major product. The glycosidation of sugar derivative 4 with sarsasapogenin 23 gave beta-glycoside 24 (29.1%) and alpha-glycoside 25 (46.9%), and that of 12 with 23 gave beta-glycoside 26 (24.0%) and alpha-glycoside 27 (40.8%). The improvement of the yields of beta-glycosides 24 and 26 (66.9 and 62.1% for 24 and 26, respectively) in the glycosidations were accomplished by the employment of alpha-bromides 28 and 29 obtained from 4 and 6, respectively. The glycosidations of monoglycosides 30 and 31 obtained by the treatment 24 and 26, respectively, with ammonia-saturated ether with sugar acetate bromides 32 and 34 gave diglycoside derivatives 35 and 33, respectively.