Helquinoline, a new tetrahydroquinoline antibiotic from Janibacter limosus Hel 1+.

The ethyl acetate extract of cultures of Janibacter limosus showed a high biological activity against bacteria, and fungi and delivered two new natural products, a tetrahydroquinoline derivative designated as helquinoline (1), and the N-acetylkynuramine (3a), along with other known secondary metabolites. The structure of 1 has been elucidated as 4-methoxy-2-methyl-1,2,3,4-tetrahydroquinoline-8-carboxylic acid on the basis of 1D and 2D NMR and mass spectra. The relative stereochemistry of the compound 1 was assigned as 2R*,4R* with the aid of coupling constants, NOESY correlation and by comparison with a related compound.