ENZYMATIC-SYNTHESIS OF THE GLYCOSIDES OF CALYSTEGINES B-1 AND B-2 ANDTHEIR GLYCOSIDASE INHIBITORY ACTIVITIES

Several glycosides of calystegines B-1 and B-2 were synthesized by use of rice a-glucosidase and the whole cells of Rhodotorula lactosa, and their glycosidase inhibitory activities were investigated. Incubation of a mixture of calystegine B-1 and maltose with rice cr-glucosidase gave 3-O-alpha-D-glucopyranosylcalystegine B-1 (2, 11.3%). An enzymati c beta-transglucosylation reaction of calystegines B-1 or B-2 with cel lobiose using the whole cells of R. lactosa gave 3-O-beta-D-glucopyran osylcalystegine B-1 (1) (0.9%) or 4-O-beta-D-glucopyranosylcalystegine B-2 (3, 11.2%), respectively, while a similar beta-transgalactosylati on of calystegine B-2 from lactose gave 4-O-beta-D-galactopyranosylcal ystegine B-2 (4, 10.1%). The glycosylation of calystegines B-1 and B-2 markedly decreased or abolished their inhibition against beta-glucosi dase, alpha- or beta-galactosidase. Compound 4 however retained more o r less the potency of calystegine B-2 against trehalase. Interestingly , compound 1 was a noncompetitive inhibitor of rice alpha-glucosidase, with a K-1 value of 0.9 +/- 0.1 mu M. (C) 1997 Elsevier Science Ltd. All rights reserved.