Divergent Total Syntheses of Hetero-Oligomeric Iridoid Glycosides

Abstract

Divergent total syntheses of the hetero-oligomeric iridoid glycosides mainly found in Dipsacus asper were achieved. Thus, loganin (1), which is important as a monomer unit, was efficiently synthesized by stereoselective reductive cyclization using secologanin (2) as a substrate. Sequential condensation reactions of derivatives of 1 and 2 as monomer units led to the first enantioselective total syntheses of the heterooligomers cantleyoside, (E)-aldosecologanin, dipsaperine, (3R, 5S)-5-carboxyvincosidic acid 22-loganin ester, and dipsanoside A.

Bioinspired Total Synthesis of (+)-Kopsiyunnanine B

“…All analytical data of the synthetic 1 agreed with the reported data of the natural product, except for the optical rotation. The sign of the rotation of the natural and synthetic products were opposite, leading us to question the absolute stereochemistry (synthetic 1; 18 D −15.9 (c 0.1, CHCl 3 ). On the other hand, the electronic circular dichroism (ECD) spectra were in perfect agreement.…”

“…We have recently achieved a collective total synthesis of monoterpenoid indole alkaloids along a biosynthetic tree diagram. [13][14][15][16][17][18][19][20][21] In this study, we conceived an alternative biosynthetic hypothesis for 1 (Chart 2). Our proposed biosynthesis begins with a connection by the reductive amination of tryptamine and secologanin (2).…”