[Isomeric phenanthridines from 1,2-dihydro-5-methyl-2'-nitro-[1,1'-biphenyl]-2,6-dicarboxylic acid esters].

Hydrolysis of the dienamine function of the dihydrobiphenyls 3 leads to a mixture of the tautomers 4A-C (NMR). The structures of the starting material 3a and the products 4cA and 4bC are confirmed by X-ray crystal analysis. The biphenyls 5 are formed by dehydrogenation of 3 with iodine, whereas 4b produced the additional iodinated compound 6. 4b reacts with manganese dioxide to yield the phenol 7a. Irradiation of the dihydrobiphenyls 3 with UV-A light gives the nitrosobiphenyls 8. In contrast, the nitrobiphenyl 7b and the lactam 10a are formed as photo products from 4c. The reduction of the nitro group of 5 with Fe/AcOH leads to the isomeric phenanthridines 10 and 11 by cyclization, whereas after reaction with Zn/NH4Cl the cyclic hydroxamic acids 12 and 13 are isolated. Compound 7a reacts with Zn/acetate buffer to yield only the hydroxamic acid 12. Ring closure takes place on treating the nitrosobiphenyls 8 with conc. hydrochloric acid, to yield the chloro-substituted hydroxamic acids 14. The half wave potentials of the dihydrobiphenyls 3 and 4 are measured by anodic oxidation using a rotating platinum electrode by means of differential pulse voltammetry. The dienamines 3 are more sensitive towards oxidation than the reference drug nifedipine; in contrast, the carba-analogues 4 are much more stable. The cyclic hydroxamic acids 13 and 14a are tested for their ability to inhibit 5-, 12- and 15-lipoxygenase. Compound 13 represents a weak inhibitor of 5-lipoxygenase in human whole blood.