G. Büchi

Formation of water-solubleMonascus red pigments by biological and semi-synthetic processes

SummaryNew water-soluble red pigments were produced byMonascus sp. in a chemically defined fermentation medium containing glutamate as nitrogen source. They were isolated and characterized as glutamate derivatives of the well-known orangeMonascus pigments (monascorubrin and rubropunctatin). The new pigments have several advantages over the known redMonascus pigments (rubropunctamine and monascorubramine) including very high water-solubility, higher absorption coefficient, and greater resistance to decoloration by light. Adding glutamate, glycine or leucine to a resting-cell system led to the formation of specific water-soluble red pigments corresponding to the exogenous amino acid. The water-soluble red pigments produced by resting-cells have retention times identical to those of the corresponding red derivatives made chemically from the orange pigments in methanol-phosphate buffer at pH 7. The hydrophobicities of the amino acid sources correspond to the HPLC retention times of the red pigments derived from them.

The absolute stereostructure of copaene

Abstract Authentic copaene has been isolated from two sources. The cadinane carbon skeleton and the position of the double bond has been confirmed. By a series of steps involving aromatisation of one ring, and by another sequence resulting in the isolation of a cyclobutanone, copaene has been shown to contain cyclobutane ring. The structure deduced, together with the conversion of copaene to (−)-cadinene dihydrochloride permits the allocation of the absolute stereostructure (VI) to this sesquiterpene.

Minor alkaloids of Aspidosperma subincanum mart.: isolation, structure proof and synthesis of 1,2-dihydro-ellipticine, 1,2-dihydro-ellipticine methonitrate and ellipticine methonitrate

Abstract Three alkaloids named in the title were isolated from the Peruvian plant “Quillo-bordon.” The structures assigned were confirmed by partial syntheses.

Constitution of verbenalin

Abstract In agreement with earlier work catalytic reduction of verbenalin gave tetrahydroverbenalin and a hydroxy-δ-lactone, desoxyverbanol. Oxidation of desoxyverbanol furnished a keto lactone which was converted to (+)-iridomyrmecin of known relative and absolute configuration by desulfurization of its ethylenethioketal. The formation of β-methylglutaric acid on ozonation of verbenalin allows placement of the ketone function in the glucoside. Verbenalin was shown to be a methyl ester by hydrolysis to the corresponding acid which could be reconverted to the natural product by esterification with diazomethane. Comparison of the UV spectra of verbenalin and verbenalol with those of tetrahydro-desoxyplumieride and bakankosin derivatives revealed the nature of the chromophore. Configurations are assigned to all asymmetric centers and a possible relationship of verbenalin to loganin is discussed.

A synthesis of gymnomitrol

Abstract Condensation of 1,2 - dimethylcyclopentene 10 with 2 - methyl - 4,4,5 - trimethoxycyclohexa - 2,5 - dienone 7 in methylene chloride - nitromethane with added stannic chloride gave a mixture of the two diastereomeric bicyclo[3.2.1]octanes 13 and 14 by ionic [4 + 2)cycloaddition. After selective reduction of the saturated carbonyl group with sodium borohydride, and hydrogenation of the double bond the two epimers 18 and 20 (ratio 3.3:1) were separable by chromatography. Protection of the hydroxy group in 18 with dihydropyran and, reduction of the α-methoxyketone 19 with calcium in liquid ammonia gave ketone 21. Gymnomitrol 1 was then prepared by Wittig olefination followed by deprotection of the hydroxy group.

Oxidative dimerization of allylic sulfones with iodine and with ferric chloride

Abstract Lithium salts of allylic sulfones are oxidized with ferric chloride-dimethyl-formamide complex mainly to 1,6-disulfones by 3-3′ coupling. Products resulting from coupling of 3,3-disubstituted sulfones undergo Cope rearrangement affording vicinal disulfones with threo-configuration. Coupling with iodine results in mixtures containing mainly vicinal disulfones, again with threo-configuration.

Aspersitin-a new metabolite of aspergillus parasiticus

Abstract The structure of aspersitin, a new metabolite of Aspergillus parasiticus was determined by X-ray analysis, and by spectroscopic measurements.

Total synthesis of racemic dehydrofuropelargones

Abstract The two racemic dehydrofuropelargones 12 and 13 were prepared by total synthesis and found to be identical with the natural furopelargones C and D respectively.

THE CHEMISTRY OF SOME MYCOTOXINS

The toxicity and carcinogenicity of the aflatoxins, metabolites of Aspergillus flavus, a common and widely distributed food spoilage fungus, contradicts the suspicions of many extremists that all environmental contaminants are produced by chemists. The biological properties of these toxins are summarized and their metabolic fate in experimental animals is discussed. Syntheses of the known metabolites, aflatoxins M 1 and P 1 , are outlined and their toxicities compared with those of the parent aflatoxin B 1 .

The synthesis of aspersitin

Abstract Aspersitin, a new metabolite produced by A s p e r g i l l u s p a r a s i t i c u s , was synthesized in racemic form by a six step sequence starting with dimethylphloroglucinol.