1. Institute of Pharmaceutical Sciences, Hiroshima University
School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima 734, Japan
2. Department of Chemistry, Ateneo de Davao University, Davao City, Philippines
3. Department of Science and Technology, Bicutan, Manila, Philippines
From the Philippine Boraginaceae medicinal plant, Ehretia microphylla Lam., rosmarinic acid (1) was isolated through bioassay-guided fractionation as an active constituent for anti-allergic property. Further study on the same plant afforded the isolation of a series of active compounds, microphyllone (2) allomicrophyllone (3) and their congeners. From the related species, Ehretia philippinensis A.DC., unique noncyanogenic cyanoglucosides, ehretioside A1 (4), B (5) and their congeners were isolated along with bioactive 1. Chemical structures of 1-5 were elucidated by means of spectroscopic (various modes of NMR) and chemical evidence. Biogenesis and structure-activity relationship of these compounds will be discussed.