Nonthmicin, a Polyether Polyketide Bearing a Halogen-Modified Tetronate with Neuroprotective and Antiinvasive Activity from Actinomadura sp.

Nonthmicin (1), a new polyether polyketide bearing a chlorinated tetronic acid, was isolated from the culture extract of a soil-derived Actinomadura strain. The structure of 1 was elucidated by interpretation of NMR and MS spectroscopic data, and the absolute configuration of 1 was proposed on the basis of the crystal structure of its dechloro congener ecteinamycin (2) also isolated from the same strain. Tetronic acids modified by halogenation have never been reported from natural products.

29-Deoxymaklamicin, a new maklamicin analogue produced by a genetically engineered strain of Micromonospora sp. NBRC 110955.

Maklamicin is a spirotetronate-class antibiotic produced by Micromonospora sp. NBRC 110955, and a polyketide assembly line and a glycerate utilization system are involved in its biosynthesis. One tailoring step in the biosynthesis is predicted to be post-polyketide synthase (PKS) modification, which seems to be catalysed by putative cytochrome P450 monooxygenases, MakC2 and/or MakC3.

Hikiamides A-C, Cyclic Pentadepsipeptides from Fusarium sp. TAMA 456.

Three new cyclic pentadepsipeptides, hikiamides A-C (1-3), were isolated from the culture extract of Fusarium sp. TAMA 456. The structures were determined by spectroscopic analysis using NMR and MS, and the absolute configurations were established by using Marfey's method and chiral HPLC analysis.

Isolation and biosynthesis of preussin B, a pyrrolidine alkaloid from Simplicillium lanosoniveum.

A new pyrrolidine alkaloid, preussin B (1), was isolated from the culture extract of the fungus Simplicillium lanosoniveum TAMA 173 along with the known congener preussin (2). The structure and absolute configuration of 1 were determined by spectroscopic analysis and spectral comparison with 2. Feeding experiments with 13C-labeled precursors revealed that the pyrrolidine ring of 1 was assembled from acetate and l-phenylalanine by a PKS-NRPS hybrid biosynthetic pathway.

Marianins A and B, prenylated phenylpropanoids from Mariannaea camptospora.

Marianins A (1) and B (2), two new prenylated phenylpropanoids, were isolated from the culture extract of the fungus Mariannaea camptospora. Structures of marianins were elucidated by interpretation of NMR and other spectroscopic data. 1 is a 5-methylcoumarin bearing two prenyloxy groups, while 2 is an orcinol derivative substituted with a 3,3-dimethyl-4-pentenoyl chain.