Process for preparing antiparasitic agents

A process for preparing a compound of the formula ##STR5## wherein X represents a single or double bond;

• R.sup.1 is OH;
• provided that when X is a single bond, R.sup.1 is OH, and when X is a double bond, R.sup.1 is absent;
• R.sup.2 is H, C.sub.1 -C.sub.8 alkyl, C.sub.2 -C.sub.8 alkenyl, C.sub.2 -C.sub.8 alkynyl, alkoxyalkyl or alkylthioalkyl containing from 1 to 6 carbon atoms in each alkyl or alkoxy group, wherein any of said alkyl, alkoxy alkenyl or alkynyl groups may be substituted by one or more halo atoms;
• or a C.sub.3 -C.sub.8 cycloalkyl or C.sub.5 -C.sub.8 cycloalkenyl group, either of which may be substituted by methylene or one or more C.sub.1 -C.sub.4 alkyl groups or halo atoms;
• or a 3 to 6 membered oxygen or sulphur containing heterocyclic ring which may be saturated, or fully or partially unsaturated and which may be substituted by one or more C.sub.1 -C.sub.4 alkyl groups or halo atoms;
• or a group of the formula SR.sup.5 wherein R.sup.5 is C.sub.1 -C.sub.8 alkyl, C.sub.2 -C.sub.8 alkenyl, C.sub.2 -C.sub.8 alkynyl, C.sub.3 -C.sub.8 cycloalkyl, C.sub.5 -C.sub.8 cycloalkenyl, phenyl or substituted phenyl wherein the substituent is C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or halo, or a 3 to 6 membered oxygen or sulphur containing heterocyclic ring which may be saturated, or fully or partially unsaturated and which may be substituted by one or more C.sub.1 -C.sub.4 alkyl groups or halo atoms;
• R.sup.3 is hydrogen or methyl;
• and R.sup.4 is a 4'-(alpha-L-oleandrosyl)-alpha-L-oleandrosyloxy group of the formula ##STR6## which comprises fermenting a Streptomyces avermitilis mutant organism ATCC 53567 or 53568, in the presence of a carboxylic acid of the formula R.sup.2 CH.sub.2 CO.sub.2 H, wherein R.sup.2 is as previously defined, or a salt, ester, or amide thereof or oxidative precursor therefor, and isolating the compound of formula (I).