Kasugamycin is a new aminoglycosidic antibiotic, effective against a variety of microorganisms, including Piricularia oryzae and Pseudomonas aeruginosa^1~3).

The effects of the antibiotic on protein and nucleic acid syntheses were investigated in reference to the mechanism of action. The results are presented in this publication. It was observed that kasugamycin markedly inhibits polyuridylate-directed polyphenylalanine synthesis. The results obtained indicated that it selectively interferes with protein synthesis and the mode of action appears to be similar to that of other aminoglycosidic antibiotics, including streptomycin and kanamycin.

Recent studies have shown that human sera possess bactericidal effects and that these effects can be modified^{1, 2)}. The present work was undertaken to see if the serum has any antifungal property. Effect of serum on the growth of Candida albicans was, therefore, studied. Its effect on the activity of some antifungal antibiotics was also studied.

Cycloheximide was isolated by Whiffen, Bohonos and Emerson^1l) from streptomycin culture of S. griseus, and its structure was elucidated by Kornfeld et al²⁾. The absolute configuration of the antibiotic was recently elucidated on the basis of optical rotatory dispersion and n.m.r. analysis by Djerassi and coworkers³⁾, Okuda and Suzuki⁴⁾ and Starkovsky and Johnson⁵⁾. The antibiotic has been used as an agricultural fungicide, rat-repellent and a drug against Cryptococcus meningitis. The antibiotic moreover has antitumor and antiprotozoa activities, however, its applications are restricted within narrow limits owing to considerable toxicity to plants and animals.

The purpose of this investigation is to synthesize more useful derivatives of cycloheximide. The present paper deals with the preparations and properties of a number of esters of the antibiotic and presents the evaluation of their antitoxoplasmic activities.