Abstract: Maytansinoids of the formula: ##STR1## wherein R is hydrogen or alkyl of 1 to 15 carbon atoms are produced by contacting, in the presence of a carbodiimide, maytansinol with a carboxylic acid of the formula:R--COOHwherein R has the same meaning as defined above.In accordance with a second aspect of the invention there are provided novel maytansinoids of the formula ##STR2## wherein R' is hydrogen, n-butyl or alkyl of 5 to 15 carbon atoms.

Abstract: Maytansinoid compounds are produced by(a) treating a compound of the formula ##STR1## wherein alk is ##STR2## --CH.sub.2 CH.sub.2 CH.sub.3 or ##STR3## under conditions of reductive hydrolysis to yield maytinsinol; and (b) contacting the maytansinol with an acid of the formula ##STR4## wherein R is lower alkyl, in the presence of a carbodiimide to yield a maytansinoid.In accordance with a second aspect of the invention there is provided a D-form maytansinoid with respect to the asymmetric center at the 2'-position having the formula: ##STR5## wherein R is a lower alkyl group.

Abstract: Maytansinoid compounds are produced by contacting in the presence of a carbodiimide the compound maytansinol ##STR1## with an acid of the formula: ##STR2## wherein R is lower alkyl, to yield the desired maytansinoids HAVING THE RESULTANT FORMULA: ##STR3## wherein R is lower alkyl. The maytansinoids (I) are both antifungal agents and also antitumor agents.The D-form (with respect to assymetry at the 2'-position) of the maytansinoids (I) represents a new class of compounds having antifungal and antitumor properties.

Abstract: A novel antibiotic B-98891, which is produced by culturing a strain of microorganisms belonging to the genus Streptomyces, shows remarkable combatting effect against microorganisms causing plant diseases. Compositions containing the antibiotic are useful for controlling diseases in plants with less undesirable side effects.