Isolation and Characterization of α,β-Unsaturated γ-Lactono-Hydrazides from Streptomyces sp.

Two novel α,β-unsaturated γ-lactono-hydrazides, geralcin A (2) and geralcin B (3), were isolated from Streptomyces sp. LMA-545. This unusual scaffold consists of the condensation of alkyl-hydrazide with an α,β-unsaturated γ-lactone, 3-(5-oxo-2H-furan-4-yl)propanoic acid (1), which was isolated from the same broth culture. Amberlite XAD-16 solid-phase extraction was used during the cultivation step, and the trapped compounds (1–3) were eluted from the resin with methanol. The structures were elucidated using 1H, 13C, and 15N NMR spectroscopic analysis and high-resolution mass spectrometry. Geralcin B (3) was cytotoxic against MDA231 breast cancer cells with an IC50 of 5 μM.