Design, synthesis, and biological evaluation of conformationally constrained aci-reductone mimics of arachidonic acid

An efficient and convergent synthesis has been developed for the production of 3,4-dihydroxy-5-[4-(2-((2Z)-hexenyl)phenyl)-3 -(1Z)-butenyl]-2(5H)-furanone (12d). This hydrophobic antioxidant is a stable conformationally constrained mimic of arachidonic acid (AA) (I) and its respective aci-reductone analogue ia). Pd(0)-catalyzed cross-coupling of 5-(3-butynyl)-3,4-dihydroxy-2( (5H)-furanone (7) with 2-((2Z)-hexenyl)iodobenzene (8d) followed by Lindlar catalyzed hydrogenation produces 12d. Butynyl intermediate 7 is prepared from 2-(benzyloxy)-5-deoxyascorbic acid (15) by iodination (I-2, PPh3, Imd), iodo substitution with lithium acetylide ethylenediamine complex (LiAEDA, HMPA, -5 degrees C), and benzyl group cleavage (Ac2O, Pyr BCl3). The utility of this synthetic method was demonstrated by the synthesis of analogues 10e-k. Biological testing revealed that certain of these antioxidants inhibit both cyclooxygenase (COX) and 5-lipoxygenase (5-LO) with comparable efficacy as reported for aspirin and zileuton, respectively. The antioxidant activity of these aci-reductones, measured as a function of their inhibitory effect on CCl4-induced lipid peroxidation of hepatic microsomes, exceeds that produced by alpha-tocopherol. Synthetic routes and initial structure-activity relationships (SAR) for these novel mixed functioning antioxidants are presented.