Tetrocarcin Q, a New Spirotetronate with a Unique Glycosyl Group from a Marine-Derived Actinomycete Micromonospora carbonacea LS276

A new spirotetronate glycoside tetrocarcin Q (1) and six known analogues tetrocarcin A (2), AC6H (3), tetrocarcin N (4), tetrocarcin H (5), arisostatin A (6), and tetrocarcin F1 (7) were isolated from the fermentation broth of the marine-derived actinomycete Micromonospora carbonacea LS276. Their chemical structures were established on the basis of 1D- and 2D-NMR spectroscopy, as well as HR-ESI-MS analysis. The absolute configurations of their stereogenic carbons were determined by circular dichroism (CD) analysis. Compound 1 possesses 2-deoxy-allose, which is a unique sugar type at the C-9 position. This type has not been found in the previously reported spirotetronate glycosides. Compound 1 displayed moderate antibacterial activity against Bacillus subitlis ATCC 63501 with minimum inhibitory concentration (MIC) value of 12.5 μM.