There is provided EtO.sub.2 C--CH.sub.2 --(R)Cgl--Aze--Pab--OH, or a pharmaceutically-acceptable salt thereof, in a form which is substantially crystalline. It has been found that crystalline forms of EtO.sub.2 C--CH.sub.2 --(R)Cgl--Aze--Pab--OH have a high chemical and solid state stability when compared to amorphous forms of the compound.

The invention concerns a new process for the preparation of apovincaminic acid ester derivatives of the general formula (I) ##STR1## wherein R.sup.1 and R.sup.2 independently represent an alkyl group having 1 to 6 carbon atoms, and pharmaceutically acceptable salts thereof. According to the invention the apovincaminic acid ester derivatives of the general formula (I) are prepared by reacting the corresponding 9- and/or 10- and/or 11-halo-14-oxo-15-hydroxyimino-E-homo-eburnane derivatives with an alkanol of the general formula R.sup.1 --OH, wherein R.sup.1 is as defined above, and with a dehydrating concentrated acid, and subsequently reducing the 9- and/or 10- and/or 11-halo-apovincaminic acid esters obtained, selectively on the aromatic ring. Alternatively, the 9- and/or 10- and/or 11-halo-apovincaminic acid esters can also be used as starting materials. The invention includes the preparation of racemic and optically active apovincaminic acid ester derivatives and of their pharmaceutically acceptable salts, as well.

The invention relates to a new process for the preparation of alkoxyvincaminic acid esters of the formula (I) ##STR1## and/or alkoxyapovincaminic acid esters of the formula (II) ##STR2## wherein R.sup.1, R.sup.2 and R.sup.3 independently stand for alkyl groups having from one to 6 carbon atoms. The compounds of the formulae (I) and (II) are pharmaceutically active, thus some of them show psychostimulant activity.

New salts of the formula XIIIa and XIIIb are disclosed ##STR1## wherein R.sup.2, R.sup.3 and R.sup.5 are each C.sub.1 to C.sub.6 alkyl and A.sup.- is an anion of a pharmaceutically acceptable acid. Furthermore new compounds of the formula XIVa and XIVb are disclosed: ##STR2## wherein R.sup.2 and R.sup.3 are as defined above. The new salts and compounds are intermediates in the preparation of 10-bromo-vincaminic acid esters. In addition the new salts and compounds have the ability to increase blood circulation and to decrease blood flow resistance in an animal subject while at the same time maintaining a steady pulse rate and blood pressure.

There is provided EtO.sub.2 C--CH.sub.2 --(R)Cgl--Aze--Pab--OH, or a pharmaceutically-acceptable salt thereof, in a form which is substantially crystalline. It has been found that crystalline forms of EtO.sub.2 C--CH.sub.2 --(R)Cgl--Aze--Pab--OH have a high chemical and solid state stability when compared to amorphous forms of the compound.