No abstract

Acid-catalyzed degradation of cyclosporin A was studied in various solvents and products of reaction were monitored by HPLC. Identification of amino acids and their chirality were determined after hydrolysis and derivatization by GC-MS. Cyclosporin H was isolated as the principal product and its structure was determined by X-ray diffraction: Cyclosporin H- diethyl ether-water (1 : 0.5 : 1) crystallizes in the monoclinic space group I2 with a = 12.338(2) Å, b = 18.963(2) Å, c = 34.074(3) Å, β = 96.47(2)°, Z = 4, and V = 7 921.4(17) Å3.

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Homoisoleucine, an unusual amino acid recently discovered in the structure of the ergopeptine alkaloid ergogaline, was determined in the parasitic fungus Claviceps purpurea Fr. (Tul.). growing on rye Secale cereale (L.) and in its host plant. Free homoisoleucine was detected by gas chromatography-mass spectrometry (GC-MS) in the amino acid pool of sclerotia of all fungal strains examined. Since homoisoleucine was not detected in rye, it seems that the amino acid is synthetized by the fungus. Furthermore, the ratio of leucine/homoisoleucine in the free amino acid pool of sclerotia is in good agreement with the ratio of the corresponding alkaloids a-ergokryptine/ ergogaline estimated by high performance liquid chromatography (HPLC). Thus, homoisoleucine is incorporated into the ergopeptines randomly with the similar specificity as leucine.