GB1000528A - 18-o-acyl-17-hydroxy-yohimbane derivatives - Google Patents

Abstract

The invention comprises: (a) lactones of formula <FORM:1000528/C2/1> where R represents a hydrogen atom or a methoxy radical and Y is a tetrahydropyran or tetrahydrofuran group, and (b) a process for the preparation of yohimbane derivatives of formula <FORM:1000528/C2/2> in which Ac is the residue of an organic carboxylic or sulphonic acid, R is a hydrogen atom or methoxy radical and R1 is a C1-C3 alkyl radical, wherein an acid of Formula I where R1 and Ac represent H is either reacted with dicyclohexyl carbodiimide or is heated with acetic acid acetic anhydride and the intermediate 17-O-acetyl compound subsequently carefully saponified with a weak organic or inorganic base, or the corresponding 3-epi acid is heated with acetic acid-acetic anhydride, epimerization at the C3 atom occurring at the same time, and the intermediate 17-O-acetyl compound subsequently carefully saponified with a weak organic or inorganic base, to give the 17-hydroxy-g -lactone, the 17-hydroxyl group of which is then protected by acetal formation and the products transformed by alcoholysis with an alkali metal alcoholate in the corresponding C1-C3 alcohol into an 18-hydroxy ester, the latter converted to the appropriate acyl compound by esterification, and the acetal group split off by acid hydrolysis. Suitable weak inorganic and organic bases for the saponification of the 17-O-acetyl compound obtained as intermediate are alkali metal bicarbonates and triethylamine. The protection of the hydroxyl group of the -lactone by an acetal group preferably takes place by reaction with dihydrofuran or dihydropyran with the addition of an acid such as p-toluene sulphonic acid or anhydrous hydrochloric acid, in an inert solvent, e.g. dimethylformamide. The esterification of the 18-hydroxy ester may be performed by reaction with acid anhydrides in pyridine or by use of acid imidazolides. The acids used as starting materials can be obtained by alkaline saponification of methyl pseudoreserpate or 3-epi-methyl pseudoreserpate obtainable from reserpine, rescinnamine or deserpidine. The reaction mixture obtained in the production of these acids may be used directly for the process according to the invention. Specifications 915,779 and 937,598 are referred to.