Premium
Über ein neues Glykosidierungsverfahren Synthese von Epipodophyllotoxin‐β‐ D ‐glucopyranosid. 21. Mitt. Über mitosehemmende Naturstoffe [1]
Author(s) -
Kuhn M.,
Von Wartburg A.
Publication year - 1968
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19680510719
Subject(s) - chemistry , pyranose , stereochemistry , glucoside , trisaccharide , glycoside , stereoselectivity , glycosidic bond , aldose , organic chemistry , catalysis , medicine , alternative medicine , pathology , enzyme
A new method for the synthesis of glycosides is described. Epipodophyllotoxin ( 4 ) reacts with 2,3,4,6‐tetra‐O‐acetyl‐β‐ D ‐glucopyranose in the presence of BF 3 ‐etherate at low temperature to yield tetra‐O‐acetyl‐epipodophyllotoxin‐β‐ D ‐glucopyranoside ( 6 ). This compound, which is sensitive to acid and base, can be converted into the free glucoside 8 by zinc acetate catalysed methanolysis. Glycosidation of podophyllotoxin ( 1 ) occurs under the same conditions but is associated with an inversion at C‐1 of the aglycone moiety, leading also to the acetylated epi ‐glucoside 6 . It is assumed that the glycosidation proceeds through a common carbonium ion intermediate ( 12 ), generated from 1 and 4 respectively by the action of BF 3 . The intermediate 12 is substituted by the pyranose component from the less hindered side, giving exclusively 1‐ epi derivatives ( e.g. 6 ). The glycosidation reaction is also highly stereoselective with respect to the glycosidic linkage. The stereochemistry of this bond is determined by the configuration at C‐1 of the pyranose compound employed for the glycosidation. Further experimental evidence for the proposed mechanism consists in the glycosidation of diphenylmethanol ( 14 ) to the corresponding β‐ D ‐glucoside 15 . Scope and limitation of the new glycosidiation method are briefly discussed.