IUPAC Congresstionality in the 'left-hand' side-chain can, of course, be written down. However, on the basis of the results above, we can conclude that there is much less scope for modification of the structure of methyl monates in the 'left-hand' side-chain than there is at the 'right-hand' side. Finally it is worth noting that the mixtures approach described above was useful here because of a specific set of circumstances: (1) most, if not all, of the analogues in the series were very weak inhibitors or inactive; (2) there was an expectation, based on the potency of compounds with the natural 'lefthand' side-chain, that high activity could be achieved with a suitable synthetic compound; (3) an enzyme assay, with sensitivity over at least four orders of magnitude, was in place; and (4) the chemistry leading to the esters was high-yielding and sufficiently robust to work with mixtures of compounds (as, to an adequate extent, was the ether chemistry). Clearly, this approach is quite unsuitable for conventional series of analogues in which most or many have some activity; In the course of the screening for novel, naturally occurring pesticides from the plant family Meliaceae, an extract of the stem bark of Aglaia roxburghiana was found to exhibit significant insecticidal activity. In addition to rocaglamide, a known insecticide isolated from several species of the genus Aglaia, 15 new natural products were isolated from this plant. Isolation and structure elucidation of the natural products is described. The outstanding insecticidal activities of some of the compounds as well as a structure–activity relationship study are presented; Hairy root cultures have been derived from neem (Azadirachta indica A Juss, Family Meliaceae) using Agrobacterium rhizogenes and Contract/grant sponsor: Commission of the European Union. Contract/grant no: FAIR-CT-96-5014. (Received 4 August 1998; accepted 16 December 1998) * Correspondence to: Athanasios K Zounos, Department of Zoology, University of Aberdeen, Tillydrone Avenue, AB24 2TZ, UK.