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An efficient scalable route to synthesize the enantiomerically pure tert-butyl-(1R,4S,6R)-4-(hydroxymethyl)-3-azabicyclo[4.1.0]heptane-3-carboxylate is described. Compared to the original routes, significant improvements were made by using an innovative approach starting from commercially available chiral lactone. In this approach, one of the key steps described is an elegant epimerization/hydrolysis of the undesired diastereoisomer avoiding tedious purification. The chemistry has been scaled up to produce kilogram amounts of tert-butyl-(1R,4S,6R)-4-(hydroxymethyl)-3azabicyclo[4.1.0]heptane-3-carboxylate in 43% yield over nine chemical transformations.

A case study on the synthesis of novel CRF-1 antagonists containing the 2,3-dihydro-1H-pyrrolo[2,3-b]pyridine moiety is presented. The development of ever more efficient synthetic routes allowed the progression of three candidates at the same time. A manufacturing route was identified and successfully demonstrated on a pilot-plant scale to prepare 100 kg of the CRF-1 antagonist GW876008.

The family of phosphodiesterase (PDE) enzymes hydrolyse cyclic nucleotides, cAMP and cGMP, leading to their inactivation as intracellular second messengers. Inhibition of these enzymes leads to an elevation of levels of cyclic nucleotides in the cell and prolongs their action on downstream signaling pathways. PDE4, of which there are four subtypes, is widely expressed throughout the brain but is also abundant in the periphery in inflammatory and immune cells, in the gastrointestinal tract, and in cardiac myocytes. GSK356278 1 is a potent, selective, and competitive inhibitor of PDE4 enzymes currently under investigation for the treatment of CNS disorders. The initial synthetic route developed by Medicinal Chemistry Department, used several hazardous and/or expensive reagents and harsh conditions and gave relatively low yields. By targeted process of research and development plus application of analytical techniques to identify byproduct and extensive route scouting, a novel synthetic route for 1 has been developed. This contribution reports the optimisation of the chemical synthesis of 1 to develop a large-scale process suitable for its synthesis.