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Mersacidin (1) is a new peptide antibiotic containing /?-methyllanthionine. It is classified as a memberof the proposed lantibiotic group of antibiotics, and is produced by a species of Bacillus. Mersacidin has a molecular weight of 1,824 (C80H120N20O21S4). The antibiotic is active against Gram-positive organisms including methicillin-resistant Staphylococcus aureus, but has no activity against Gram-negative bacteria or fungi.

Salmycin A–D, Antibiotics from Strep tomy ces violaceus, DSM 8286, Having a Siderophor‐Aminoglycoside Structure Salmycin B (2) and C (3) were isolated under acid conditions, under which they are stable, from the culture broth of Streptomyces violaceus, DSM 8286. The acid‐ and alkaline‐labile, native main component salmycin A (1), as well as salmycin D (4), were obtained under strictly neutral pH conditions. The compounds 1 (C41H70FeN7O21), 2 (C41H69FeN6O21), 3 (C40H67FeN6O21), and 4 (C40H68FeN7O21) are classified as sideromycins and are stable when dry. Mild alkaline hydrolysis of 1 and 2 yielded the known siderophor danoxamin (5; C27H46FeN5O11), and amino‐disaccharides. The amino‐glycoside 6 (C14H25NO11) of salmycin B was stabilized by hydrogenation and the structure of the corresponding peracetate 10 determined by 1H,1H‐ and 1H,13C‐correlation NMR spectroscopy (Table 1). Compound 6 consists of a glucos‐2‐ulose unit which is linked to the 2‐position of a 6‐deoxy‐6‐(methylamino)heptopyranose. The danoxamin is bonded via the carboxy group by ester linkage to the primary alcohol of the glucos‐2‐ulose. Salmycin A (1) is a natural oxime of 2, it was synthesized from 2 with hydroxylamine. The salmycins and those derivatives which contain hexapyranos‐2‐ulose form stable ketone hydrates which can be identified by mass spectrometry. Although several recently identified features of the danomycins do not correspond with those of the salmycins, 13C‐NMR spectra show that both groups of antibiotics are closely related. All salmycins, especially component 1, are highly active against Staphylococci and Streptococci, even against resistant strains of these pathogens.

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Microbial natural products are a rich source of bioactive molecules to serve as drug leads and/or biological tools. We investigated a little-explored myxobacterial genus, Nannocystis sp., and discovered a novel 21-membered macrocyclic scaffold that is composed of a tripeptide and a polyketide part with an epoxyamide moiety. The relative and absolute configurations of the nine stereocenters was determined by NMR spectroscopy, molecular dynamics calculations, chemical degradation, and X-ray crystallography. The compound, named nannocystin A (1), was found to inhibit cell proliferation at low nanomolar concentrations through the early induction of apoptosis. The mode of action of 1 could not be matched to that of standard drugs by transcriptional profiling and biochemical experiments. An initial investigation of the structure-activity relationship based on seven analogues demonstrated the importance of the epoxide moiety for high activity.

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