Antiparasitic agents and process for their preparation.

THE INVENTION PROVIDES NOVEL COMPOUNDS HAVING THE FORMULA:(FORMULA 1)WHEREIN THE BROKEN LINE AT THE 22-23 POSITION REPRESENTS AN OPTIONAL DOUBLE BOND AND WHEREIN R1 IS H OR OH AND THE DOUBLE BOND IS ABSENT, OR, THE DOUBLE BOND IS PRESENT AND R1 IS ABSENT; R2 IS AN ALPHA-BRANCHED C3-C8 ALKYL, ALKENYL, ALKYNYL, ALKOXYALKYL OR ALKYLTHIOALKYL GROUP; A C3-C8 CYCLOALKYL, C5-C8 CYCLOALKENYL OR C5-C8 CYCLOALKYLALKYL GROUP, ANY OF WHICH MAY OPTIONALLY BE SUBSTITUTED BY METHYLENE OR ONE OR MORE C1-C4 ALKYL GROUPS OR HALO ATOMS; OR A 3 TO 6 MEMBERED OXYGEN OR SULPHUR CONTAINING HETEROCYCLIC RING WHICH MAY OPTIONALLY BE SUBSTITUTED BY ONE OR MORE C1-C4 ALKYL GROUPS OR HALO ATOMS; R3 IS HYDROGEN OR METHYL; R4 IS H OR 4''-(ALPHA-L-OLEANDROSYL)-ALPHA-L-OLEANDROSYLOXY, WITH THE PROVISO THAT WHEN R2 IS ALKYL IT IS NOT ISOPROPYL OR SEC-BUTYL, AND WHEN R4 IS H, R1 IS OH, AND THE DOUBLE BOND IS ABSENT, R2 IS NOT 2-BUTEN-2-YL,, 2-PENTENE-2-YL OR 4-METHYL-2-PENTENE-2-YL. THE COMPOUNDS ARE BROAD SPECTRUM ANTIPARASITIC AGENTS HAVING UTILITY AS ANTHELMINTICS, ECTOPARASITICIDES, INSECTICIDES AND ACARICIDES. THE INVENTION ALSO PROVIDES A PROCESS FOR PRODUCING THE NOVEL AVERMECTIN AND MILBEMYCIN DERIVATIVES BY ADDING A CARBOXYLIC ACID OR DERIVATIVE THEREOF TO A FERMENTATION OF AN AVERMECTIN OR MILBEMYCIN PRODUCING ORGANISM.