Abstract: Antiparasitic compounds of formula (I): ##STR1## The broken line at the 22-23 position representing an optional double bond and either R.sup.1 is H or OH and the double bond is absent or the double bond is present and R.sup.1 is absent; R.sup.2 is optionally substituted phenyl, or a group of formula (II): ##STR2## wherein X is O, S or --CH.sub.2 --, abc and d are 0-2 and a+b+c+d.ltoreq.5 R.sup.3 is H or MeR.sup.4 is H, OH or 4'-(alpha-L-oleandrosyl)-alpha-L-oleandrosyloxy.The compounds are prepared by fermentation of Streptomyces avermitilis in the presence of an N-alkanoyl cysteamine thioester containing R.sup.2.

Abstract: A new acidic polycyclic antibiotic UK-61,689 has the formula: ##STR1## or a pharmaceutically acceptable cationic salt thereof. The antibiotic and its cationic salts are active against a variety of microorganisms and are effective in controlling coccidiosis, enteritis and swine dysentery as well as being effective in promotion of growth and/or improving efficiency of feed utilization in swine and ruminants.

Abstract: Antiparasitic compounds of formula (I): ##STR1## The broken line at the 22-23 position representing an optional double bond and either R.sup.1 is H or OH and the double bond is absent or the double bond is present and R.sup.1 is absent; R.sup.2 is optionally substituted phenyl, or a group of formula (II): ##STR2## wherein X is O, S or --CH.sub.2 13 , abc and d are 0-2 and a+b+c+d.ltoreq.5R.sup.3 is H or MeR.sup.4 is H, OH or 4'-(alpha-L-oleandrosyl)-alpha-L-oleandrosyloxy.The compounds are prepared by fermentation of Streptomyces avermitilis in the presence of an N-alkanoyl cysteamine thioester containing R.sup.2.

Abstract: A new acidic polycyclic antibiotic UK-61,689 has the formula: ##STR1## or a pharmaceutically acceptable cationic salt thereof. The antibiotic and its cationic salts are active against a variety of microorganisms and are effective in controlling coccidiosis, enteritis and swine dysentery as well as being effective in promotion of growth and/or improving efficiency of feed utilization in swine and ruminants.

Abstract: Antiparasitic compound of formula (I): ##STR1## The broken line at the 22-23 position representing an optional double bond and eitherR.sup.1 is a H or OH and the double bond is absent or the double bond is present and R.sup.1 is absent;R.sup.2 is optionally substituted phenyl, or a group of formula (II): ##STR2## wherein X is O, S or --CH.sub.2 --, abc and d are 0-2 and a+b+c+d.ltoreq.5 R.sup.3 is H or MeR.sup.4 is H, OH or 4'-(alpha-L-oleandrosyl)-alpha-L-oleandrosyloxy.The compounds are prepared by fermentation of Streptomyces avermitilis in the presence of an N-alkanoyl cysteamine thioester containing R.sup.2.

Abstract: A new acidic polycyclic antibiotic UK-61,689 has the formula: ##STR1## or a pharmaceutically acceptable cationic salt thereof. The antiobiotic and its cationic salts are active against a variety of microorganisms and are effective in controlling coccidiosis, enteritis and swine dysentery as well as being effective in promotion of growth and/or improving efficiency of feed utilization in swine and ruminants.

Abstract: A new acidic polycyclic antibiotic UK-61,689 has the formula: ##STR1## or a pharmaceutically acceptable cationic salt thereof. The antibiotic and its cationic salts are active against a variety of microorganisms and are effective in controlling coccidiosis, enteritis and swine dysentery as well as being effective in promotion of growth and/or improving efficiency of feed utilization in swine and ruminants.