Masayoshi Okano

Lasiodiplodin, a potent antileukemic macrolide from Euphorbia splendens

Abstract In vivo P-388 assay-directed fractionation of an active extract from Euphorbia splendens has led to the isolation of lasiodiplodin, a potent antileukemic macrolide, the structure of which was established from spectral data and a single-crystal X-ray analysis.

Mechanism of eukaryotic protein synthesis inhibition by brusatol.

The mechanism by which brusatol inhibits protein synthesis in rabbit reticulocytes has been investigated. When added to reticulocyte lysates, brusatol inhibits endogenous protein synthesis only after a lag of 2-4 min at 30 degrees C. During this period 80 S ribosomes accumulate. Brusatol is equally effective in inhibiting endogenous protein synthesis in lysates and poly(U)-directed polyphenylalanine synthesis with runoff ribosomes. In fractionated reticulocyte systems, brusatol does not inhibit formation of the ternary, 40 S, and 80 S initiation complexes, but does inhibit the reaction of puromycin with initiation complexes containing [35S]Met-tRNAf. These data suggest that brusatol inhibits the peptidyl transferase elongation reaction of protein synthesis, but can do so only after one round of protein synthesis has been completed. Thus, the mechanism of action of brusatol in the rabbit reticulocyte system is very similar to the effects previously reported for bruceantin in a yeast system.

The Reaction of Monoketones with Manganese(III) Acetate

When acetone, ethyl methyl ketone (EMK), and cyclohexanone were heated with manganese(III) acetate dihydrate in a mixed solvent of glacial acetic acid and acetic anhydride at 100 °C, acetoxy ketones were obtained as common products. Furthermore, ketone dimers (1,4-diketones) were obtained from acetone and cyclohexanone, which also gave 1,2,3,4-tetrahydrodibenzofuran. When mixtures of these ketones and 1-hexene were heated with the oxidant, saturated and unsaturated ketones and γ-acetoxy ketones were obtained as common products, and 2-propylchromene was obtained as a new product from the cyclohexanone-1-hexene mixture. The formation courses of these reaction products are discussed.

Structure of bisclausarin, a new bicoumarins from Citrus plant

A new type bicoumarin, named bisclausarin, was isolated from the roots of Citru hassaku (Rutaceae) and the structure was elucidated as 1 on the basis of spectroscopic data