Separation and NMR studies on lignans of Raulinoa echinata.

Investigation of the leaves of Raulinoa echinata Cowan (Rutaceae) has led to the isolation of several furofuran (2,6-diaryl-3,7-dioxabicyclo[3.3.0]-octane) lignan derivatives, namely (+)-sesamin, (+)-eudesmin, (+)-methylpiperitol (= kobusin), (+)-piperitol-gamma,gamma-dimethylallylether and the corresponding epi compounds: (+)-asarinin, (+)-epieudesmin, (+)-methylxanthoxylol, (+)-methylpluviatilol, (+)-xanthoxylol-gamma,gamma-dimethylallylether and (+)-pluviatilol-gamma,gamma-dimethylallylether. This is the first report of the chromatographic separation of the epimers (+)-methylxanthoxylol/(+)-methylpluviatilol and (+)-xanthoxylol-gamma,gamma-dimethylallylether/(+)-pluviatilol-gamma,gamma- dimethylallylether and of their NMR nOe difference studies.

A polyketide synthase in glycopeptide biosynthesis: the biosynthesis of the non-proteinogenic amino acid (S)-3,5-dihydroxyphenylglycine.

Balhimycin, a vancomycin-type antibiotic from Amycolatopsis mediterranei, contains the unusual amino acid (S)-3,5-dihydroxyphenylglycine (Dpg), with an acetate-derived carbon backbone. After sequence analysis of the biosynthetic gene cluster, one gene, dpgA, for a predicted polyketide synthase (PKS) was identified, sharing 20-30% identity with plant chalcone synthases. Inactivation of dpgA resulted in loss of balhimycin production, and restoration was achieved by supplementation with 3,5-dihydroxyphenylacetic acid, which is both a possible product of a PKS reaction and a likely precursor of Dpg. Enzyme assays with the protein expressed in Streptomyces lividans showed that this PKS uses only malonyl-CoA as substrate to synthesize 3,5-dihydroxyphenylacetic acid. The PKS gene is organized in an operon-like structure with three downstream genes that are similar to enoyl-CoA-hydratase genes and a dehydrogenase gene. The heterologous co-expression of all four genes led to accumulation of 3,5-dihydroxyphenylglyoxylic acid. Therefore, we now propose a reaction sequence. The final step in the pathway to Dpg is a transamination. A predicted transaminase gene was inactivated, resulting in abolished antibiotic production and accumulation of 3,5-dihydroxyphenylglyoxylic acid. Interestingly, restoration was only possible by simultaneous supplementation with (S)-3,5-dihydroxyphenylglycine and (S)-4-hydroxyphenylglycine, indicating that the transaminase is essential for the formation of both amino acids.

Arenosclerins A-C and haliclonacyclamine E, new tetracyclic alkaloids from a Brazilian endemic Haplosclerid sponge Arenosclera brasiliensis.

Arenosclerins A (2), B (3), and C (4), as well as haliclonacyclamine E (1), are new tetracyclic alkylpiperidine alkaloids isolated from a new species of marine sponge belonging to the order Haplosclerida, Arenosclera brasiliensis, a species endemic to the southeastern Brazilian coast. The alkaloids were isolated as their hydrochloride salts and identified by analysis of spectroscopic data. Data obtained from (1)H-(1)H COSY, HMBC, and HSQC-TOCSY NMR experiments allowed complete assignment of the (1)H and (13)C resonances, and analysis of the NOESY and ROESY spectra showed that the only differences between 2, 3, and 4 were the relative stereochemistries of the bispiperidine ring system. Arenosclerins A-C are the first haliclonacyclamine/halicyclamine-related alkaloids with a hydroxy group in the bridging alkyl chain.

N-acetyl-gamma-hydroxyvaline lactone, an unusual amino acid derivative from a marine streptomycete.

We report the isolation and structure elucidation of N-acetyl-gamma-hydroxyvaline lactone (1) from a streptomycete obtained from marine sediments collected in the north coastline of São Paulo State, Brazil.