TAN-950A

A novel antifungal amino acid antibiotic, TAN-950 A ([S]-2-amino-3-(2,5-dihydro-5-oxo-4-isoxazolyl)propanoic acid), was found to have affinity for three excitatory amino acid (EAA) receptors and to inhibit [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA), [3H]kainate and [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid ([3H]CPP) binding competitively. It caused excitation of rat hippocampal CA1 neurons in vitro, an effect that was antagonized by an AMPA/kainate antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX). Chemical modification of TAN-950 A brought about a large change in its pharmacological activity. Alkylation at the C-3 position of the isoxazolone ring markedly increased the ability to elicite neuronal firing. This agonistic effect was also antagonized by DNQX. The (R) enantiomer of TAN-950 A had increased selectivity for the N-methyl-D-aspartate (NMDA) receptor subtype. This selectivity was further enhanced by removal of the methylene group from the amino acid moiety. The most potent NMDA agonistic activity was observed with [R]-2-amino-2-(2,5-dihydro-3-methyl-5-oxo-4-isoxazolyl)acetic acid. These derivatives of TAN-950 A might be useful agents for investigating the pharmacological and physiological roles of EAA receptors.

Two isoxazolylalanine isomers, beta-(isoxazolin-5-on-2-yl)-L-alanine (BIA, 1) and beta-(isoxazolin-5-on-4-yl)-L- alanine (TAN-950A, 2) were confirmed to be derived from O-acetyl-L-serine (OAS) and isoxazolin-5-one by cysteine synthases (CSases) with a different ratio in different plant parts. Some properties of this enzyme in the biosynthesis of both isomers are described.

A novel antifungal antibiotic, TAN-950 complex, was isolated from the culture filtrate of Streptomyces platensis A-136 (IFO 14603, FERM BP-1786). The water-soluble amphoteric substances in this complex were purified by chromatography using ion-exchange resins, QAE-Sephadex and adsorptive resins and were designated TAN-950 A and TAN-950 A-E mixture. The molecular formula of TAN-950 A was determined to be C6H7N2O4Na for the sodium salt. This new amino acid antibiotic showed antifungal activity against Candida albicans in vitro and in vivo, and had low toxicity in mice.