Three novel enantiomeric pairs of bromolactones possesing a 2,5-dimethylphenyl substituent at the β-position of the lactone ring have been synthesized from corresponding enantiomeric (E)-3-(2',5'-dimethylphenyl)hex-4-enoic acids (4) by kinetically controlled bromolactonization with N-bromosuccinimide (NBS). γ-Bromo-δ-lactones (5) were isolated as the major products. Absolute configurations of stereogenic centers of γ-bromo-δ-lactones (5) were assigned based on X-ray analysis; configurations of cis δ-bromo-γ-lactones (6) and trans δ-bromo-γ-lactones (7) were determined based on mechanism of bromolactonization. Synthesized compounds exhibited significant antiproliferative activity towards the four canine cancer cell lines (D17, CLBL-1, CLB70, and GL-1) and one human cancer line (Jurkat). Classifying the compounds in terms of activity, the most active were enantiomers of trans δ-bromo-γ-lactones (7) followed by enantiomers of cis isomer (6) and enantiomeric γ-bromo-δ-lactones (5). Higher activity was observed for all stereoisomers with S configuration at C-4 in comparison with their enantiomers with 4R configuration. Synthesized compounds did not induce hemolysis of erythrocytes. The results of the interaction of bromolactones with red blood cell membranes suggest that these compounds incorporate into biological membranes, concentrating mainly in the hydrophilic part of the bilayer but have practically no influence on fluidity in the hydrophobic region. The differences in interactions with the membrane between particular enantiomers were observed only for γ-lactones: stronger interactions were found for enantiomer 4R,5R,6S of cis γ-lactone (6) and for enantiomer 4S,5R,6S of trans γ-lactone (7).
Keywords: absolute configurations; antiproliferative activity; biological membranes; bromolactonization; erythrocytes; hemolytic activity; lactones.