Further studies on metabolism in vivo of 3,4,3′,4′-tetrachlorobiphenyl in rats: Identification of minor metabolites in rat faeces

Abstract

1. Metabolism in vivo of 3,4,3′,4′-tetrachlorobiphenyl (TCB) was investigated in male Wistar rats.

2. Five new minor metabolites in addition to two previously identified major metabolites (5-hydroxy-3,4,3′,4′-TCB and 4-hydroxy-3,5,3′,4′-TCB) were isolated as methylated derivatives from faeces of rats treated with 3,4,3′,4′-TCB, by silica gel column chromatography and subsequent preparative t.l.c.

3. Among these methylated metabolites, three were identified as dimethoxy-TCB, and one as monomethoxy-trichlorobiphenyl (TriCB), by g.l.c.-mass spectrometry. By comparison with synthetic standards they were fully identified as 2,5-dimethoxy-3,4,3′,4′-TCB, 4,4′-dimethoxy-3,5,3′,5′-TCB, 5,6-dimethoxy-3,4,3′,4′-TCB, and 4-methoxy-3,3′,4′-TriCB, respectively. The structures of these metabolites in rat faeces should therefore be 2,5-dihydroxy-3,4,3′,4′-TCB, 4,4′-dihydroxy-3,5,3′,5′-TCB, 5,6-dihydroxy-3,4,3′,4′-TCB, and 4-hydroxy-3,3′,4′-TriCB.

4. One further metabolite was isolated, which was shown to be an oxepin, existing in a state of equilibration with the 4′,5′-oxide of the major metabolite, 4-hydroxy-3,5,3′,4′-TCB, by mass and ¹H-n.m.r. spectra. On standing for several months, this metabolite isomerized to a new compound with a different g.l.c. retention time, which on methylation yielded a product identical with synthetic 4,4′-dimethoxy-3,5,3′,5′-TCB by g.l.c.-mass spectrometry. From these results this metabolite was assumed to be an oxepin, equilibrated with 4-hydroxy-4′,5′-epoxy-3,5,3′,4′-TCB.