摘要：

A process is disclosed for obtaining the R,R isomer of: ##STR1## wherein R 1 and R 2 may be one or more groups which may be the same or different and are selected from the group consisting of hydrogen, C 1 to C 4 alkyl, C 1 to C 4 alkoxy, hydroxy, halogen, trifluoromethyl, carboxy, hydroxyalkyl, alkoxycarbonyl, C 1 to C 4 thioalkyl, sulfonyl and sulfinyl; X is a divalent radical consisting of ##STR2## wherein R' is hydrogen; R 2 and R 3 may be the same or different and are selected from the group consisting of hydrogen and C 1 to C 4 alkyl; R 5 and R 6 are selected from the group consisting of hydrogen, carboxy, alkoxycarbonyl, hydroxymethyl, --CH 2 OCH 2 COOR 7 and --CH 2 OCH 2 CH 2 OR 7 where R 7 is hydrogen or C 1 to 4 alkyl; except that R 5 and R 6 may not both be hydrogen; and the asterisks denote asymmetric carbon atoms; said process comprising the steps of: (a) reacting Mosher's acid with a compound of formula I to attach a group of the formula ##STR3## at the N-9 position of a mixture of (+) and (-) enantiomers of said compound to form a new pair of diastereoisomers; and (b) separating said new pair of diastereoisomers by HPLC and recovering the R,R isomer. The process is based on reacting Mosher's acid with the compound of formula I and thereafter using HPLC to separate the R,R isomer.

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