Second derivatives of the UV spectra of 2-(4-alkoxybenzyl)cyclopentan-l-ols and their acetates were used for the quantitative analysis of reaction kinetics of enzyme-mediated hydrolytic processes. To determine the enantiomeric purity of the products using non-chiral HPLC columns, their diastereoisomeric esters of 3,3,3-trifluoro-2methoxy-2-phenylpropanoic acid (MTPA) were prepared. The absolute configuration of the products was established using a combination of the results of a HPLC analysis and *H/19F-NMR measurements of the diastereoisomeric MTP esters. The analytical method described consists of an easy routine HPLC analysis which can sometimes be used as a quick on-line analysis of the reaction kinetics and as a quick stepwise analysis of the optical purity and the absolute configuration of the products.
Introduction.
-During our research, we often have to analyze reaction mixtures in which chiral compounds are products of enzyme-mediated resolution reactions involving racemic parent substrates. It is obvious that the UV spectra of the racemic parent substrates and the chiral products should be very similar or even identical. In this research, we focused our attention on the derivatives of 2-(4-alkoxybenzyl)cyclopentan-1-01s 1-6 (Scheme I ) , the enantiomers of which are useful chiral intermediates in the synthesis of insect juvenile hormone analogs. Enzymic transesterifications studied with the isomers of 2-(4-methoxybenzyl)cyclopentanol ( i e . , with the structures analogous to 1 and 2) has been published recently [l] [2]. The main products la-12a (i.e., the main chiral products 7a-12a and the deracemized substrates la-6a) of the enzymic process involving 1-6 as substrates are shown in Scheme I , together with the corresponding minor products 1 b-12 b of which were determined by the analytical method described below and are considered to be optical impurities of 1 a-12a.
Due to the presence of an aromatic ring in the structure, the compounds 1 -12 display characteristic UV spectra showing two maxima, at 1 ca. 220 and 280 nm (Fig. ). The latter of these two maxima is the lower one, but its second-order derivative shows important features, which may be used in the on-line HPLC analysis of reaction kinetics, The second-order derivative of the UV maximum at A ca. 280 nm displays several thin minima, the intensity of which is dependent on the concentration of the compound studies in the reaction mixture. Such a concentration dependence was reported by Piot and coworkers to be linear and used to develop a quantitative HPLC analysis of aromatic