Pergamon S0031-9422(96)00886-1 Phytochemistry, Vol. 42, No. 5, pp. 1377-1385, 1996 Copyright ~) 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0031-9422/96 $15.00 + 0.00 BIOGENETICALLY IMPORTANT QUINONEMETHIDES AND OTHER TRITERPENOID CONSTITUENTS OF SALACIA RETICULATA*t BHAVANI DHANABALASINGHAM, VERANJAKARUNARATNE, YASUHIRO TEZUKA,~ TOHRU KIKUCHI:~ and A. A. LESLIEGUNATILAKA§ Department of Chemistry, University of Peradeniya, Peradeniya, Sri Lanka; ,Research Institute for Wakan-Yaku,Toyama Medical and Pharmaceutical University, Sugitani, Toyama 930-01, Japan (Received in revised form 18 January 1996) Key Word Index--Salacia reticulata var. fl-diandra; Celastraceae; celastroloids; isoiguesterinol; 30-hydroxypristimerin; salacenonal; structural elucidation; biosynthesis. Abstract--Phytochemical investigation of the outer root bark of Salacia reticulata var. fl-diandra (Celastraceae) has resulted in the isolation of two novel quinonemethide triterpenoids (celastroloids), isoiguesterinol and 30-hydroxypristimerin, along with salacenonal, several known celastroloids and friedo-oleanane triterpenoids. Details of the structural elucidation and 1H and ~3C NMR spectral assignments of these compounds are presented and their biogenetic significance is discussed. INTRODUCTION Salacia reticulata Wight (Celastraceae) is a medicinal plant with restricted distribution in Sri Lanka and India. Two varieties of S. reticulata have been recognized in Sri Lanka; S. reticulata growing in submontane forests in the centre of the island and S. reticulata var. fl- diandra growing in the low country rain forests of the south. In traditional medicine of Sri Lanka, an aqueous infusion of the roots of S. reticulata is used in the treatment of diabetes [2] and its oral hypoglycaemic activity has been demonstrated in experimental rats [3]. Salacia species are known to elaborate antho- cyanidines, catechins, phenolic acids, quinones, friedo- oleananes, quinonemethide and related triterpenoids (celastroloids), mangiferin, gutta-percha and dulcitol [4-7]. Previous phytochemical studies on S. reticulata have resulted in the isolation of gutta-percha [8], sitosterol [8], pristimerin (4) [8], mangiferin [9], epi- kokoondiol [1], salacenonal (7) [10] and salaciquinone (8) [11] from the root bark, and iguesterin, pristimerin and epi-kokoondiol from the stem bark [12]. In con- tinuing our interest in the triterpenoids of Celastraceae [1, 10, 11] and search for biosynthetic congeners of celastroloids [10, 13], we have investigated the outer *Part 28 in the series 'Studies on Terpenoidsand Steroids.' For part 27 see ref. [1]. tDedicated to the memory of the late Prof. Sinnathamby Balasubramaniam, a dear friend and an eminent botanist. §Author to whom correspondence should be addressed. Present address: Departmentof Chemistry, Virginia Polytech- nic Institute and State University,B lacksburg,VA 24061-0212, U.S.A. root bark of S. reticulata var. fl-diandra, which led to the isolation of two new biogenetically important celastroloids, isoiguesterinol (1) and 30-hydroxy- pristimerin (2) along with several known celastroloids and friedo-oleanane triterpenoids. In this paper we report the detailed structural elucidation of 1, 2 and 7, another biogenetically important nortriterpenoid recent- ly reported [10]. This also constitutes the second report of the natural occurrence of netzahualcoyene (10) previously isolated from Maytenus horrida (Celas- traceae) [14]. RESULTSAND DISCUSSION The dried and powdered root outer bark of S. reticulata var. fl-diandra was successively and exhaus- tively extracted with hot hexane and benzene. Although the two extracts exhibited similar TLC patterns, a close examination revealed that the hexane extract contained a higher percentage of the less polar constituents, whereas the benzene extract contained more of the polar compounds. Therefore, the hexane extract was used to isolate the less polar constituents, and the benzene extract to obtain more polar ones. Thus, the two extracts were separately fractionated by silica gel column chromatography using solvent combinations of hexane and ethyl acetate of increasing polarity. The column fractions were combined using TLC as a guide and further purified as necessary by silica gel flash chromatography and/or preparative TLC to obtain 13 compounds, of which two were new. The hexane extract yielded (in order of increasing polarity) 7, 8, fl-amyrin, isoiguesterin (9), 10, 4, 1377