Glycosylation of cardenolides. VIII. Structures of the by-products of the synthesis by the orthoester method of strophanthidol rhamnosides
The by-products formed in the preparation of strophanthiodol 19-rhamnoside and 3, 19-bisrhamnoside by the orthoester method are 3β,5-dihydroxy-8,19-epoxy-5β,14β, 17α-card-20(22)-enolide and its 3-α-L-rhamnoside. 3β,5-Dihydroxy-8,19-epoxy-5β, 14α,17β-card-20(22)-enolide has been obtained by the action of a solution of HBr in nitromethane on strophanthidol.
SYNTHESIS OF β-D-MANNOSE 1,2-ORTHOACETATES
Synthesis of 3,4,6-tri-O-acetyl-β-D-mannopyranose 1,2-orthoacetates (I) from 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl bromide (II) and various alcohols in the presence of pyridine and substituted pyridines is described. 2,6-Lutidine is a particularly effective acid acceptor in these condensations, and the use of chloroform as a diluent is advantageous. The lutidine-buffered system has afforded a good yield of orthoacetate (I) with several alcohols that barely react with II in the presence of silver ion; this difference is attributed to the dominance of side reactions under the latter conditions. The N-bases also promote a more highly stereoselective orthoester synthesis than does the silver-catalyzed reaction, leading to formation of the OR-exo-diastereoisomer almost exclusively.
Separation of 21-deoxy-δ4-3-oxo-steroids of the pregnane series by thin — Layer chromatographic procedures
Abstract A method is proposed for the separation and characterisation of forty 21-deoxy-Δ 4 -3-oxo-steroids of the pregnane series by means of thin-layer chromatography. The method includes one-dimensional thin-layer chromatography on silica gel G, formation and separation of π -complexes with unsaturated steroids on silica gel G / silver nitrate chromatoplates, hydrazone formation by elatographic procedures and “in situ” developed colour reactions. The influence of primary, secondary and tertiary hydroxyl groups as well as ketonic groups at different positions of the steroid ring on the Chromatographic behaviour of the steroid is discussed.