Neoantimycins A and B, Two Unusual Benzamido Nine-Membered Dilactones from Marine-Derived Streptomyces antibioticus H12-15.

An actinomycete strain (H12-15) isolated from a sea sediment in a mangrove district was identified as Streptomycesantibioticus on the basis of 16S rDNA gene sequence analysis as well as the investigation of its morphological, physiological, and biochemical characteristics. Two novel benzamido nonacyclic dilactones, namely neoantimycins A (1) and B (2), together with the known antimycins A1ab (3a,b), A2a (4), and A9 (5), were isolated from the culture broth of this strain. Compounds 1 and 2 are the first natural modified ATNs with an unusual benzamide unit. The structures of these new compounds, including their absolute configuration, were established on the basis of HRMS, NMR spectroscopic data, and quantum chemical ECD calculations. Their cytotoxicities against human breast adenocarcinoma cell line MCF-7, the human glioblastoma cell line SF-268, and the human lung cancer cell line NCI-H460 were also tested. All compounds exhibited mild cytotoxic activity. However, Compounds 1 and 2 showed no activity against C. albicans at the test concentration of 1 mg/mL via paper disc diffusion, while the known antimycins showed obvious antifungal activity.

Measurement of the degree of coupled isotopic enrichment of different positions in an antibiotic peptide by NMR.

An experimental strategy for determining the extent to which multiply isotopically labeled fragments are incorporated intact into relatively complicated compounds of interest is presented. The NMR methods employed are based on isotope-filtered one-dimensional spectra and difference HSQC spectra incorporating a spin echo designed to report on the presence of a second NMR active isotope at a coupled site. They supplement existing methods for determining the extent of isotopic incorporation at individual sites to reveal whether two coupled labeled sites in a precursor are incorporated as an intact unit into products. The methods described also circumvent 1H signal overlap and distinguish between the effects of different nitrogens coupled to individual carbons. The somewhat complicated case of valclavam illustrates the method's utility in measuring the J coupling constants between 13C and nearby sites that are only fractionally labeled with 15N, and measuring the fraction of molecules in which 13C is coupled to 15N, at each of several sites. The 15N of [2-13C, 15N]-labeled glycine is found to be incorporated into all three N positions of valclavam but most heavily into the N11 position. Specifically, 15N and 13C are incorporated into the N11 and C10 positions together as an 15N13C fragment approximately 8% of the time, whereas 15N is incorporated largely independently at the other positions.

Improved production of pentostatin and identification of fermentation cometabolites.

A practical process is described for the large-scale isolation of pentostatin, an adenosine deaminase inhibitor used clinically for the treatment of interferon-refractory hairy cell leukemia. The identities of minor components in the fermentation beer, including 2'-deoxyguanosine, are also reported.