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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.

A new C23 polyacetylene diol was isolated from the marine sponge S. truncata and its structure was elucidated mainly on the basis of its spectral data.

SPECIALIAThe editors do not hold themselves responsible for the opinions expressed in the authors' brief reports. -Les auteurs sont seuls responsables des opinions exprimdes dans ces br6ves communications. -Fiir die Kurzmitteilungen ist ausschliesslich der Autor verantwortlich. -Per le brevi comunicazioni 6 responsabile solo l'autore. -OTBexcvBeHHocxb 3a KOpOTI-(14~ COO~IIIeHYI!~t HeCeT 14CI(YIIOqllTeJINHO aBTOp. --SOlO lOS autores son responsables de las opiniones expresadas en estas comunicationes breves.Summary. From the marine sponge Cacospongia scalaris, scalaradial 1, desacetylscalaradial 2, and heteronemin 3 were isolated. Compound 2 showed potent cell growth inhibition. The stereochemistry of 3 is briefly discussed.Sponge material (collected at Wakayama) frozen with dry ice, was immersed in dichloromethane. Reverse phase chromatography (LiChroprep RP-18/MeOH) of the dichloromethane layer, which showed mainly 2 spots (dialdehyde components 1 and 2; Rf= 0.20 and 0.25, respectively) under UV light on TLC plate, resulted in a change of both spots which made them undetectable by UV light (cyclic dimethylacetal 4 and 5; Rf=0.40 and 0.47, respectively). Further chromatography of 4 and 5 resulted in separation of each into 2 epimers (4a, 4b and 5a, 5b, respectively). Treatment of either 4a or 4b in dichloromethane with hydrochloric acid gave a dialdehyde, which proved to be scalaradial 1, a metabolite from the sponge C. molliofl '3, based on its spectra. Inferring that formation of cyclic dimethylacetals from dialdehyde was catalysed by a trace amount of acid remaining on the RP-18 support during reverse phase chromatography, we treated 1 with ion exchange resin (acid form) in methanol. As expected, cyclic dimethylacetals 4 a and 4 b were formed.