Pergamon 0031-9422(93)E0068-P Phytochemistry, Vol. 35, No. 5, pp. 1163-1166, 1994 Copyright 9 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0031 9422/94 $6.00+0.00 A DIHYDROISOCOUMARIN GLUCOSIDE FROM ALOE HILDEBRAND TII NIGEL C. VEITCH,* MONIQUE S. J. SIMMONDS, WALLYM. BLANEYt and TOM REYNOLDS Jodrell Laboratory, Royal Botanic Gardens. Kew, Richmond, Surrey, TW9 3AB, U.K.; tDepartment of Biology, Birkbeck College, London, WCIE 7HX, U.K. (Received 27 August 1993) Key Word Index--Aloe hildebrandtii; Aloeaceae; dihydroisocoumarin glucosides; leaf exudate phenol- ics; chemotaxonomy; anti-insect activity. Abstract--The first dihydroisocoumarin glucoside reported from Aloe has been isolated from the leaf exudate of A. hildebrandtii and its structure determined to be 3,4-dihydro-6,8-dihydroxy-3-(2'-acetyl-Y-O-fl-D-glucopyranosyl-5'- hydroxyphenyl) methyl-2 (1H)-benzopyran-1-one by one- and two-dimensional NMR spectroscopy. An assessment is made of the potential chemotaxonomic value and anti-insect activity of this compound. INTRODUCTION Aloe hildebrandtii Baker is a medium sized plant of shrubby growth and sprawling habit, native to North Somalia [1]. In a recent chemotaxonomic survey, this species was affiliated with A. jacksonii Reynolds and A. cremnophila Reynolds and Bally [2]. The presence of a TLC zone staining purple with Fast Blue B was noted among the leaf exudate phenolics of all three species [2]. The compound in this zone, corresponding to that label- led 'P20' in a previous study, is found in 250 of the 240 species of Aloe surveyed [3]. As well as the new affiliation mentioned above, an alternative grouping has included A. hildebrandtii with other shrubby species mainly from consideration of habit [1, 4] and with a smaller subgroup within these on the basis of chromatographic patterns of leaf exudate phenolics [5, 6]. The compound P20 has now been isolated from the leaf exudate of A. hildebrandtii and shown to be the dihydroisocoumarin glucoside I. Al- though the absolute configuration of 1 (at C3) has not yet been determined, its structure is closely related to that of the corresponding aglycone termed 'feralolide', recently reported from a commercial pharmaceutical preparation known as 'Cape Aloes' [7]. The dihydroisocoumarin glucoside 1 also appears to be a useful chemotaxonomic marker within the genus Aloe. Despite the extensive literature on the effects coumarins can have on insect behaviour [8], little information is available concerning the anti-insect activity of dihydroisocoumarins. This study examines the effect of 1 on the feeding behaviour of a range of iepidopteran larvae to assess potential biolo- gical activity. *Author to whom correspondence should be addressed. OH 0 OH RESULTSAND DISCUSSION Separation of the leaf exudate phenolics of A. hilde- brandtii was achieved by column chromatography on silica gel eluted with methanol in chloroform, followed by final purification on reverse-phase silica gel eluted with a gradient of methanol in water. The compound corres- ponding to the purple-staining TLC zone P20 and having a R z value of 0.50 was isolated as a buff powder. Molecu- lar structure determination involved extensive use of one- and two-dimensional 1H and laC NMR spectroscopy, and enabled 1 to be identified as a new dihydroisocoum- arin glucoside. The NMR data are presented in Tables 1 and 2, with the latter including all the assigned heteronuc- lear proton and carbon connectivities required to unam- biguously define the structure. Use of the HMBC experi- ment was found to be particularly valuable in this respect. Although the spectroscopic parameters relating to the aglycone moiety of 1 were determined independently, they are in agreement with those obtained for the Cape Aloe product feralolide [7] and therefore do not warrant further discussion. Small differences in chemical shift values for the assigned carbon atoms in Table 1 reflect the different conditions under which data were collected for the two compounds, with the exception of those associ- ated with carbon atoms in the immediate vicinity of the 1163