Methylotrophic bacteria synthesis

Methoxatin, now known as coenzyme PQQ, was originally obtained from methylotrophic bacteria but is now known to be a mammalian cofactor, for example, for lysyl oxidase and dopamine p-hydroxylase. The first synthesis of this rare compound was accomplished by the route outlined below. In the retrosynthetic analysis both of the heterocyclic rings were disconnected using directly keyed transforms. 

Methoxatin (cf p. 406) is a dehydrogenase cofactor in methylotrophic bacteria (also called PQQ PQQ = pyrroloquinoUne quinone). The synthesis of its triester J is achieved by the following sequence based on 2-methoxy-5-nitroaniline (X) ... 

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