Structure and spasmolytic activity of eucalyptanoic acid from Eucalyptus camaldulensis var. obtusa and synthesis of its active derivative from oleanolic acid

Abstract

A new triterpenoid acid named eucalyptanoic acid (1) has been isolated from the fresh uncrushed leaves of Eucalyptus camaldulensis var. obtusa along with two known constituents, beta-sitosterol (2) and betulinic acid (3). The structure of 1 has been established as 3beta-hydroxyolean-9(11),12-dien-28-oic acid through spectral studies including 1D and 2D NMR. 1 and its acetyl (1a) and acetylmethyl (1b) derivatives were tested for spasmolytic activity. 1b was found to be the most active spasmolytic, mediated through blockade of calcium influx at 1 mg/mL. In the present study 1b was also prepared starting from oleanolic acid (4). Acetylation of 4 gave 4a, which on methylation afforded 4b. Reaction of 4b with N-bromosuccinimide (NBS) furnished 1b. Hence 4 may be regarded as the biogenetic precursor of 1. Compounds 4 and 4a were found inactive at 1 mg/mL, while 4b was moderately active in showing spasmolytic activity.