| Summary: | Four polyene macrolactams including the previously reported niizalactam C (<b>4</b>), and three new ones, streptolactams A–C (<b>1</b>–<b>3</b>) with a 26-membered monocyclic, [4,6,20]-fused tricyclic and 11,23-oxygen bridged [14,16]-bicyclic skeletons, respectively, were isolated from the fermentation broth of the deep-sea sediment-derived <i>Streptomyces</i> sp. OUCMDZ-3159. Their structures were determined based on spectroscopic analysis, X-ray diffraction analysis, and chemical methods. The abiotic formation of compounds <b>2</b> and <b>4</b> from compound <b>1</b> were confirmed by a series of chemical reactions under heat and light conditions. Compounds <b>1</b> and <b>3</b> showed a selective antifungal activity against <i>Candida albicans</i> ATCC 10231.
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