J Nat Prod 1998 Oct 01;6110:1248-51. doi: 10.1021/np980138j.

Tenuecyclamides A-D, cyclic hexapeptides from the cyanobacterium Nostoc spongiaeforme var. tenue.

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Four modified cyclic hexapeptides, tenuecyclamides A-D (1-4), were isolated along with the known antibiotic, borophycin (5), from the methanol extract of Nostoc spongiaeforme var. tenue (TAU strain IL-184-6). The planar structure of tenuecyclamides A-D (1-4) was determined by homonuclear and inverse-heteronuclear 2D-NMR techniques as well as by high-resolution mass spectrometry measurements. The absolute configuration of the asymmetric centers was studied by Marfey''s method for HPLC. The stereochemistry of the asymmetric centers in tenuecyclamides A and B (1 and 2) could not be fully determined, while that of tenuecyclamides C and D (3 and 4) was unambiguously determined.

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