Ether linkage, biosynthesis

All bisbenzylisoquinoline alkaloids from Berberidaceae have either (1/ , l S) or (IS, 1 R) configurations. The extra oxygen function of the C ring of thalibrun-ine (Section II,A,4), calafatine (Section II,C,9), and related alkaloids apparently arises from secondary oxidation ortho or para to the diphenyl ether linkage (57). A scheme for the biosynthesis of pakistanine (see Section II,C,52), kalashine (Section II,C,52), and related alkaloids from either a pakistanamine (Section II,B,6) or valdiberine (Section II,C, 142) precursor has been suggested (62) (see Section II,C,52). 

Figure 7.63 Proposed mechanism for the polyketide backbone rearrangement in rifamycin B biosynthesis by introducing an ether linkage between C-12 and C-29 carbons.

There are more than 350 bisbenzyhsoquinoline alkaloids now known that typically possess one or more ether linkage(s), and one or more phenyl-phenyl linkages between the two benzyhsoquinoline molecules. Although it is considered that these alkaloids are formed by various forms of the oxidative coupling between the two benzyhsoquinoline moieties, their biosynthesis is not well studied. 

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