Facile methods for preparing diketide and triketide thioesters are disclosed. The resulting thioesters may be used as intermediates in the synthesis of desired polyketides, and may contain functional groups which ultimately reside in side chains on the resulting polyketide and thus can be used further to manipulate the polyketide so as form derivatives. The polyketides produced may also be tailored by glycosylation, hydroxylation and the like. New polyketides and their derivatives and tailored forms are thereby produced.
Substituted 2-aminoalk-3-enoic acid derivative of formula I ##STR1## wherein R.sub.1 is an aliphatic hydrocarbon radical that is substituted by optionally acylated or aliphatically or araliphatically etherified hydroxy, by halogen, by optionally acylated and/or aliphatically substituted amino or by an aza-, diaza-, azoxa- or oxa-cycloaliphatic radical, or is an oxacycloaliphatic hydrocarbon radical bonded via a carbon atom, or is an optionally aliphatically N-substituted or N-acylated azacycloaliphatic hydrocarbon radical, and R.sub.2 is free or esterified carboxy, and their salts exhibit NMDA-antagonistic properties and are useful as active ingredients of anticonvulsive medicaments.