2-Hydroxyethyl-3-methyl-1,4-naphthoquinone

Indothiazinone (1), an indolyl thiazolyl ketone, was discovered in cultures of novel myxobacterial strain 706, recently isolated from compost in Germany. Molecular phylogenetic studies based on 16S rRNA gene sequences revealed strain 706 to be a representative of a new family of the Sorangiineae. A screening of the culture broth for antimicrobial metabolites followed by isolation and characterization of these compounds revealed six indole derivatives and a 1,4-naphthoquinone derivative. The structures were determined to be indothiazinone (1; 1H-indol-3-yl(1,3-thiazol-2-yl)methanone) and three 3-methylbuta-1,3-dien-1-yl-substituted indoles, indolyl ethanol 2 and the E- and Z-isomers of indolyl ethylidenehydroxylamine 4 and 5 by MS and NMR spectroscopic analyses. In the indolyl ethanol derivative 3 the unsaturated methylene group of the butadienyl residue was replaced by an oxygen atom to give the keto group of the butanone side chain. Further 1H-indol-3-ylacetonitrile (6) was identified, which was already known as a myxobacterial metabolite. 2-Hydroxyethyl-3-methyl-1,4-naphthoquinone (7) was recognized during dereplication as an antibiotic previously isolated from Actinoplanes capillaceus. Whereas 1, 4, 5, and 7 showed weak activity against yeasts and filamentous fungi, isomers 4 and 5 were weakly active against Gram-positive bacteria and mouse fibroblasts. Compound 6 is volatile, and 2 and 3 showed no activity in a number of assays.

A new deep-sea-derived actinomycete 12A22 was isolated from the sediment of the South China Sea which showed potential cytotoxic and antimicrobial activities. The actinomycete was identified as Actinoalloteichus cyanogriseus by investigating morphological characteristics and phylogenetic analyses based on its 16S rRNA gene sequence. Two compounds, cyclo-(L-Pro-D-Pro-L-Tyr-L-Tyr) (1) and 2-hydroxyethyl-3-methyl-1,4-naphthoquinone (2), were isolated and characterized from the fermentation broth of the strain 12A22. Compound 2 exhibited significant inhibitory activities against a variety of phytopathogenic fungi (Fusarium oxysporum f. sp. cucumerinum, Setosphaeria turcica, and Botrytis cinerea) and Gram-positive bacterium (Bacillus subtilis). In particular, this compound showed better antifungal activity against Botrytis cinerea than positive control amphotericin B. Besides, compound 2 showed moderate cytotoxic activity against human breast cancer MDA-MB-435 cells with IC50 10.59 µM, weaker than the positive control diaminedichloroplatinum with 5.91 μM. Our results suggested that this naphthoquinone could be used as a potential antimicrobial and antitumor agent. Supplementary information: The online version contains supplementary material available at 10.1007/s13205-021-02846-0.