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The stereochemistry of the exocyclic double bond in polyoximic acid has been revised to cis-3-ethylidene-L-azetidine-2-carboxylic acid, based on the single crystal X-ray analysis of the racemic naturally-derived acid, on NMR studies of polyoxin A, and of synthetic samples of cis- and trans-polyoximic acids.

In polyoxin-resistant strains of Alternaria kikuchiana, the synthesis of cell-wall chitin was scarcely inhibited by polyoxin B, although chitin synthetase preparations of them showed a level of polyoxin sensitivity similar to those of sensitive strains. A decrease of14C-labelled polyoxin uptake was correlated with an increased level of polyoxin resistance in various strains. The amount of14C-polyoxin A or3H-polyoxin A accumulated in a highly resistant strain was less than 10% of that in a sensitive strain. These results indicate that resistant strains have a reduced capacity to take up polyoxin A or B.

(1) Chitin-UDP acetylglucosaminyltransferase (E.C. 2.4.1.16., chitin synthetase) in the cell-free system from phytopathogenic fungus Piricularia oryzae, and effects of various polyoxins and related compounds on the enzyme activity were studied. Polyoxins A~M, polyoxin A derivatives, polyoxin C derivatives, 5′-amino-5′-deoxyuridine, uridine and thymidine inhibited equally the incorporation of N-acetylglucosamine (GlcNAc) from UDP-N-acetylglucosamine (UDP-GlcNAc) into chitin.(2) Competition between the above inhibitors and UDP-GlcNAc was observed by kinetic studies. The Km for UDP-GlcNAc was determined to be 3.3 × 10−3 m and the Ki values for polyoxins A~M, except polyoxin C, were found to be in the range of 3.3 × 10−5 m to 3.4 × 10−6 m. For polyoxin C, 5′-amino-5′-deoxyuridine and uridine, the Ki values of 2.7 × 10−3 m, 8.0 × 10−3 m and 3.0 × 10−3 m were given, respectively. The inhibitor constants for other related compounds were also calculated.(3) The values of binding affinity, −ΔG, for formation of su...

Three strains of soil Streptomyces which belong to Streptomyces cacaoi were found to produce a new antifungal antibiotic complex, polyoxin complex. Polyoxin A and B were isolated in pure forms out of it. They are amphoteric compounds with the molecular formulas, C23H32N6O14 and C17H25N5O13 respectively. They showed very specific activities against phytopathogenic fungi.

Polyoxin A, a selective inhibitor of chitin synthetase, was found to be insecticidal when injected into the abdomen of grasshoppers nymphs, with an LD50 of 1.26±0.20 μg per insect. Symptomatology and the absence of any toxicity toward adult insects indicate that toxicity is due to interference with cuticle deposition.