Extractives from the New Zealand Myrtaceae. VI. Arjunolic Acid from the Heartwood of Metrosideros umbellata

Abstract

Triterpene acids have been reported from the bark and heartwood of a number of members of the family Myrtaceae (White and Ralph 1949; White and Zampatti 1952; Arthur and Hui 1954; Corbett and McDowell 1958; Ritchie, Snape, and Taylor 1961). The genus Metrosideros is represented in New Zealand by 10 species, of which M . umbellata (ironwood) is the most abundant in the South Island. Extraction of the finely powered heartwood with ether yielded crude arjunolic acid (2.5%). Purification was effected by crystallization from methanol. This acid had previously been reported by Ritchie, Snape, and Taylor (1961), and by King, King, and Ross (1954). Acetone extraction of the ether exhausted powder gave amorphous condensed tannins (5.8%). Tests for ellagic acid in this extract were negative. This is unusual, as the family Myrtaceae belongs to the group Myrtiflora in which ellagic acid is widespread (Bate-Smith 1956). An analysis of the tannin is included in the following section.