for trapoxin B, by X-ray analysis, mass spectrometric, NMR and chemical studies.

No abstract

As the first non-peptide endothelin receptor antagonist from a higher plant, a new triterpenoid, myriceric acid A (50-235) (1) was isolated from the bayberry, Myrica cerifera. Myriceric acid A (1) inhibited not only an endothelin-1-induced increase in cytosolic free Ca2+ concentration (IC50 = 11 +/- 2 nM) but [125I]endothelin-1 binding in rat aortic smooth muscle cells (Ki = 66 +/- 15 nM). Two new related triterpenoids, myriceric acid C (6), and myriceric acid D (8), were also isolated. Furthermore, the chemical modification of these natural products led to the synthesis of sulfated derivatives (13, 14, 15) which showed 1.5 to 20 times higher affinity for endothelin receptors. The structure activity relationships of myriceric acids and their derivatives are discussed.

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Metal-containing novel heterocyclic antibiotics, micacocidin A (1), B (2), and C (3) have been isolated from the culture filtrate of Pseudomonas sp. No. 57-250. The structure and absolute configuration of micacocidin A, an octahedral Zn2+ complex, was determined by X-ray crystallographic analysis. And then, the structures of the two congeners, micacocidin B (Cu2+ complex) and C (Fe3+ complex) were investigated by employing one dimensional and two dimensional homonuclear and heteronuclear NMR spectroscopies and mass spectrometry.In the accompanied paper1), the taxonomy, fermentation, isolation, physico-chemical properties, and biological activities of micacocidin A, B, and C were reported.Herein, we describe the account of the structure determination of micacocidin A (1) and two congeners (2 and 3), metal chelated antibiotics having specific and excellent activity against Mycoplasma species (Fig. 1). Materials and Methods Spectroscopic StudiesLiquid secondary ion mass spectra (LSI-MS) were obtained by using a Hitachi M-90 mass spectrometer (BEE geometry) equipped with cesium ion gun. Samples were dispersed in 3-nitrobenzyl alcohol and introduced into the mass spectrometer on a LSI-MS target. One dimensional (1D) and two dimensional (2D) NMR were