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Myriceric acid A (1) is an oleanane triterpene that is a potent and specific endothelin A receptor antagonist. A practical procedure for large-scale synthesis of myriceric acid A (1) has been developed starting from oleanolic acid 4. The conversion of oleanolic acid 4 to the key intermediate myricerone 3 was achieved in an efficient manner employing a photochemical reaction (the Barton reaction) of nitrite 7. Our synthetic procedure alleviated several difficulties of the original Barton's procedure with regard to yields and large-scale operation. Myricerone 3 afforded Horner−Wadsworth−Emmons (HWE) type phosphonate 2 which has proved to be a versatile precursor of 1. The preparation of phosphonate 2 on a scale of several hundred grams is described. The synthesis was completed by condensation of 2 with 3,4-bis[(diphenylmethyl)oxy]benzaldehyde (21), giving α,β-unsaturated ester 22, which was deprotected to afford 1. The whole synthetic sequence is efficient (14 steps, 31% yield) and requires no chromatographic purification except to obtain the final product 1.

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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.