BIOMEDICAL AND ENVIRONMENTAL MASS SPECTROMETRY, VOL. zyxwv 16, 399402 (1988) Mass Spectrometric Study of New a-Methylene- y- lactone Carbohydrate Derivatives C. Borges and M. A. Almoster Ferreirat Department of Chemistry, Faculty of Sciences, University of Lisbon, R. Ernesto de Vasconcelos, Edit zyxw C1, 1700 Lisbon, Portugal; and Center for Mass Spectrometry of University of Lisbon, Complexo I (INIC), Av. Rovisco Pais, 1096 Lisbon Codex, Portugal A. P. Rauter Department of Chemistry, Faculty of Sciences, University of Lisbon, R. Ernesto de Vasconcelos, Edif. C1, 1700 Lisbon, Portugal A mass spectrometric study of six new a-methylene-y-lactone carbohydrate derivatives has been carried out in order to correlate the occurrence of metastable transitions with the stereochemistry of the compounds. Results indicate that the decomposition of some metastable fragment ions usually releases higher amounts of kinetic energy when the chiral centre of the lactone ring has the zyxwvu (S) configuration. However, the kinetic energy released on the decomposition of metastable molecular ions seems to follow different trends as regards the configuration of the chiral centre of the lactone moiety, when one or two isopropylidene rings are present in the molecule. This study is being extended to some related compounds in order to confirm whether the kinetic energy release is preferentially affected in a particular way by the chirality. INTRODUCTION The u-methylene-y-lactone unit, which occurs in natural sesquiterpenes, is responsible for a diversity of bio- logical activities, namely cytostatic, insecticidal, anti- feedant and plant growth activities.'.' The mechanism of its action consists of an irreversible inhibition of sul- phydryl enzymes by a Michael type reaction, in which the electrophilic methylene group is added to the sul- phydryl group of the enzyme. The u-methylene-y-lactone carbohydrate derivatives 14 have been synthesized., They are known to cause papain inhibition: and owing to their structure have potential biological importance. It has been recently shown that the orientation of certain groups in stereoisomeric structures affects the amount of kinetic energy released in the decomposition of metastable ions. The decomposition of the metastable molecular ions of compounds 14 was studied as well as that of some of their metastable fragment ions. Some results related to the loss of water, acetone, CH,' and COH' for compounds 1-6 and loss of CONH,' for compounds 3 and 4 will be discussed in order to relate the calculated kinetic energy released in each metastable transition to the stereochemistry of the compounds. EXPERIMENTAL Compounds 14 were synthesized by Reformatsky reac- tion with ethyl bromomethylacrylic ester and activated zinc in anhydrous tetrahydrofuran at 50 "C under a t Author to whom correspondence should be addressed. 0887-6134/88/240399-04 $05.00 zyxwvutsr 0 1988 by John Wiley zyxwvutsrqp & Sons, Ltd. nitrogen atm~sphere.~ The substrates used in the reac- tion were zyxw 3-O-benzyl-l,2-O-isopropylidene-u-~-xylo- pentodialdo-l,4-furanose5 for the synthesis of 1 and 2, 3-0- benzyl- 1,2-0-isopropylidene-u-~-xylo- 5-hexulo- furanur~noamide~ for obtaining compounds 3 and 4 and finally 1,2;5,6-di-O-isopropylidene-u-~-ribo- hexo- furanos-3-ulose6 for synthesizing compounds 5 and zy 6. The stereoisomeric mixtures obtained, in good yields, from the Reformatsky reaction were easily separated by column chromatography, using silica gel 23CL400 mesh, and ethyl acetate-toluene (1 : 5). Compounds 3 and 4 were separated using ethyl acetate-toluene (1 : 10). Ana- lytical thin-layer chromatography was performed on aluminium sheets coated with a 0.2 mm layer of silica gel 60 F254. Optical rotations, determined with a Perkin-Elmer 141 polarimeter, infrared (IR) spectra recorded on a Perkin-Elmer 577 spectrometer and 'H and I3C nuclear magnetic resonance spectra recorded at 300 MHz with a Bruker CXP 300, were found to be according to the original literature., Mass spectrometric studies were carried out in a modified double-focusing mass spectrometer of conven- tional geometry, equipped with an electron impact/ chemical ionization (EI/CI) dual source. Appropriate techniques for the detection of metastable ions were used scanning either the accelerating voltage (V) or the magnetic (B) and electric sector zyx (E) fields simultaneously, and focusing either the daughter ion or the parent ion as main beam (B/E and B'/E techniques). 7-9 proved to be very sensitive to the ion source tem- perature. Experiments with each of both epimers had to be carried out at different source temperatures to avoid decomposition prior to ionization. Therefore the source