Phyllanthostatin 1-Phyllanthoside Orthoacid Rearrangement

Solvolysis of phyllanthoside (lb) in 1:9 ethanol-water (14 days at room temperature) consumed about 54% of the starting glycoside and afforded the S3'-monoacetyl derivative 1f and phyllanthostatins 1 (1a) and 4 (le) in 8-10% yields accompanied by five related products of orthoacid rearrangement and/or deacetylation. Several additional minor transformation products were detected by HPLC analyses. When phyllathostatin 1 (la) was subjected to the same solvolysis reaction for 21.5 h, approximately half rearranged to phyllanthoside (lb). After 4 days the product composition resembled that from phyllanthoside. Discovery of the phyllanthostatin 1 ⇄phyllanthoside orthoacid rearrangement revealed a very important aspect of Phyllanthus glycoside chemistry and provided the first examples of 0–3 ⇄ O–4 acetyl migrations in a glucopyranoside.