Racemization of (S)-(+)-10,11-dimethoxyaporphine and (S)-(+)-aporphine: efficient preparations of (R)-(−)-apomorphine and (R)-(−)-aporphine via a recycle process of resolution

Efficient preparations of (R)-(−)-apomorphine (R)-1 and (R)-(−)-aporphine (R)-2 based on a recycle process of resolution are described. In this recycle process of resolution, (RS)-(±)-10,11-dimethoxyaporphine 3 as the precursor of 1, and (RS)-(±)-aporphine 2 were successfully resolved into both enantiomers with (+)-dibenzoyltartaric acid (DBTA). The desired (R)-3 and (R)-2 were obtained and then, respectively, transformed to compound (R)-1, the hydrochloride salt of (R)-1, diacetate compound 4 and the hydrochloride salt of (R)-2; while the undesired (S)-3 and (S)-2 were racemized to obtain a racemate, which was suitable for further resolution. A method for the racemization of the undesired (S)-3 and (S)-2 was extensively studied, in order to obtain high-yielding racemization conditions. A plausible mechanism for the racemization of (S)-3 and (S)-2 was also proposed.

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(R)-(−)-Apomorphine hydrochlorideC17H18ClNO2[α]D20=-48.1 (c 1.0, water)Source of chirality: (−)-tartaric acidAbsolute configuration: (R)

(R)-(−)-10,11-DiaetoxyaporphineC21H21NO4[α]D20=-137.1 (c 0.3, methanol)Source of chirality: (−)-tartaric acidAbsolute configuration: (R)

(R)-(−)-AporphineC17H17N[α]D20=-151.6 (c 0.6, methanol)Source of chirality: (−)-tartaric acidAbsolute configuration: (R)

(R)-(−)-Aporphine hydrochlorideC17H18NCl[α]D20=-106.6 (c 0.3, methanol)Source of chirality: (−)-tartaric acidAbsolute configuration: (R)

(R)-(−)-10,11-DimethoxyaporphineC19H21NO2[α]D20=-172.3 (c 1.4, methanol)Source of chirality: (−)-tartaric acidAbsolute configuration: (R)