Neil J. OLDHAM-1, Martin VEITH-1, Konrad DETTNER-2, Jacques
M. PASTEELS-3, and Wilhelm BOLAND-1*
1-Institut für Organische Chemie und Biochemie, Gerhard-Domagk-Str. l, D-53121 Bonn.
Germany
2-Tierökologie 11, Universitat Bayreuth, Postf 101251, D-95440 Bayreuth, Germany.
3-Laboratoire de Biologie Animale et Cellulaire, CP 160/2, Universite Libre de
Bruxelles, Avenue Franklin D. Roosevelt 50, B-1050 Bruxelles, Belgium
(7S-[2H5]-Salicylalcohol (3) and (7R)-[2H1]-salicylalcohol (5) have been synthesised in order to examine the stereospecificity of salicylalcohol oxidase ffom the defensive secretion of the salicylaldehyde producing leaf beetle Phratora vitellinae. Oxidation was found to proceed by selective removal of the C(7)-HR hydrogen atom (Re-specificity) to yield salicylaldehyde. (7S)[2H6]-Benzylalcohol (9) was also oxidised Re-specifically to benzaldehyde but in much lower yield, indicating the importance of the ortho-hydroxy-group of salicylalcohol in substrate enzyme binding.
The stereospecificities of terpenoid oxidases from six species of iridoid producing leaf beetle were examined using (1R, 8R)-[2H2]-8-hydroxygeraniol (10), and were all found to oxidise the substrate Re-specifically. Cross-activity of oxidation was found in a number of species, with P. vitellinae able to oxidise terpenoid (10) and two of the iridoid producing species able to oxidise salicylalcohol analogue (3), again with Re-specificity. However, when the two substrate analogues were presented together, in equal concentrations, preferential oxidation of the natural analogue was observed in each case.
The kinetics of oxidation for a number of terpenoid and aromatic alcohols by the defensive secretion of the iridoid producing leaf beetle Phaedon armorac)ae have been studied, revealing a large difference between the rate of (primary, allylic) terpenoid alcohol oxidation and the rate of salicylalcohol oxidation.