Process for the resolution of pyrano[3,4-b]indole-1-acetic acids
AssigneeAmerican Home Products Corporation
InventorsChristopher A. Demerson, Leslie G. Humber
Life of this patent
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Abstract
Mixtures of racemic (.+-.)pyrano[3,4-b]indole-1-acetic acids are resolved with (-)-borneol to obtain the substantially pure (+) and (-)-enantiomers. The resolution involves the formation of a mixture of the diastereoisomeric pyrano[3,4-b]indole-1-acetic acid, (-)-borneol esters, separation of the diastereoisomeric esters, and hydrolysis of the latter esters.
Claims8
A process for resolving a racemic (.+-.)-compound of formula I ##STR3## in which R.sup.1 is lower alkyl, and R.sup.2 and R.sup.3 each is hydrogen, lower alkyl or halo to obtain the corresponding (+) or (-)-enantiomer of formula I in which R.sup.1, R.sup.2 and R.sup.3 are as defined herein, which comprises:
- (a) esterifying a racemic (.+-.)-compound of formula I in which R.sup.1, R.sup.2 and R.sup.3 are as defined herein with (-)-borneol to obtain a diastereoisomeric mixture of a corresponding compound of formula II ##STR4## in which R.sup.1, R.sup.2 and R.sup.3 are as defined herein;
- (b) separating the diastereoisomers;
- (c) hydrolyzing the diastereoisomers of formula II in which R.sup.1, R.sup.2 and R.sup.3 are as defined herein with an aqueous alkaline solution;
- and
- (d) isolating the substantially pure corresponding (+) or (-)-enantiomer of formula I in which R.sup.1, R.sup.2 and R.sup.3 are as defined herein.
A process for resolving racemic (.+-.)-1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid to obtain (+)-1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid, which comprises:
- (a) esterifying racemic (.+-.)-1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid with (-)-borneol to obtain a diastereoisomeric mixture of (+) and (-)-1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid, (-)-borneol ester;
- (b) separating the (-)-diastereoisomer;
- (c) hydrolyzing the (-)-1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid, (-)-borneol ester with an aqueous alkaline solution;
- and
- (d) isolating the substantially pure enantiomer (+)-1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid.
A (+) or (-)-diastereoisomer of a compound of the formula ##STR5## in which R.sup.1 is lower alkyl, and R.sup.2 and R.sup.3 each is hydrogen, lower alkyl or halo.
Dependencies are inferred from the claim text.