Abstract: A compound of formula (I), or a salt or solvate thereof, ##STR1## in which R.sub.1 and R.sub.2 each independently represents hydrogen, alkyl, optionally substituted aryl or optionally substituted aralkyl; R.sub.3 represents alkyl, optionally substituted aryl or optionally substituted aralkyl and R.sub.4 represents alkyl or optionally substituted aryl; a process for preparing such compounds and the use of such compounds for resolving certain racemates.

Abstract: A compound of formula (I) or a pharmaceutically acceptable salt thereof, ##STR1## in which, R.sub.1 is hydrogen or lower alkyl;R.sub.2 is hydrogen or lower alkyl;R.sub.4 and R.sub.4 ' together form a group .dbd.N--Ra, or .dbd.CRaRb, where Ra is hydrogen, lower alkyl, aryl, aryloxy, lower alkylcarbonyl, arylcarbonyl, aryloxycarbonyl, lower alkoxy, lower alkoxy carbonyl, lower alkoxy carbonyl alkoxy, lower thioalkoxy, hydroxy, nitrile, heterocyclyl, or --NRcRd, where Rc is hydrogen, lower alkyl, cycloalkyl, aryl, aralkyl, lower alkylcarbonyl, arylcarbonyl, aminocarbonyl, aminothiocarbonyl, aminoiminocarbonyl, lower alkoxycarbonyl, lower alkoxythiocarbonyl, aryloxycarbonyl, thiocarbonyl, nitrile, carboxyl, heterocyclyl or heterocyclylcarbonyl, and Rd is hydrogen or lower alkyl; Rb is hydrogen, lower alkyl, aryl, lower alkylcarbonyl, lower alkoxycarbonyl, nitrile or nitro;or R.sub.4 is --NH--Ra, in which Ra is as defined above, and R.sub.4 ' is hydrogen or lower alkyl;each of R.sub.3 and R.sub.