Fungal melanins and their interactions with metals

Cyclobutanones and Cyclobutenones in Nature and in Synthesis [New Synthetic Methods(71)]

Starting from R,R-(+)-tartaric acid, the synthesis of (2S,3R,4R6E)-3-hydroxy -4-methyl-2-methylamino-6-octenoic acid in 24 steps is reported. This novel amino acid is found in the cyclic undecapeptide cyclosporin A, isolated from the fungal strain Tolypocladium inflatumGAMS. Its stereospecific synthesis allowed, for the first time, the isolation and characterization of the new amino acid previously reported as the ‘C-9-amino acid’ [1].

Synthesis of Cyclosporine. I. Synthesis of enantiomerically pure (2S,3R,4R,6E)‐3‐hydroxy ‐4‐methyl‐2‐methylamino‐6‐octenoic acid starting from tartaric acid

Aeroadaptive microaerophilic Azotobacter chroococcum 184 produced a cell-associated black pigment when grown at high aeration rates under nitrogen-fixing conditions. This pigment was shown to be a catechol melanin. Polyphenol oxidase activity was detected in cell extracts of cells grown for 72 h. Melanin formation was optimal in the later stages of growth, and there was no correlation between nitrogenase activity and melanization. Nitrogenase activity in strain 184 was optimal at 10% O2, and melanin formation was suppressed by O2 limitation. In the presence of charcoal, an adsorbent of toxic oxygen intermediates, and benzoic acid, a scavenger of hydroxyl radicals, melanization was inhibited. However, in the presence of copper, the intensity of pigment color increased and melanization was accelerated. Copper also eliminated catalase and peroxidase activities of the organism but still permitted aerobic growth. In the presence of low levels of iron, melanization was accelerated under high aeration rates, and under low rates of aeration, melanization was observed only at higher levels of iron. Hydroxamate-siderophore production was detectable in the presence of soluble iron under high rates of aeration but was repressed by the same levels of iron under low aeration rates. Unlike melanization and hydroxamate formation, catechol formation was observed under both low and high rates of aeration under nitrogen-fixing conditions. Catechol formation and melanization were repressed by 14 mM NH4+, at which level nitrogenase activity was also repressed. Copper reversed the repressive effect of NH4+. A role for catechol formation and melanization in aeroadaptation is proposed.

Catechol Formation and Melanization by Na -Dependent Azotobacter chroococcum: a Protective Mechanism for Aeroadaptation?

Strain and reactivity: Partners for selective synthesis

Vicinal alkylation of olefins, regio- and stereoselective addition of [CM + CN] units to cyclopentadiene.

A stereospecific synthesis of functionalised cyclopentene derivatives. New principle of carbon-chain lengthening.

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Vicinal alkylation of olefins, regio- and stereoselective addition of [CM + CN] units to cyclopentadiene.

A stereospecific synthesis of functionalised cyclopentene derivatives. New principle of carbon-chain lengthening.