First, Second, and Third Generation Scalable Syntheses of Two Potent H3 Antagonists

Our teams have recently completed scale-up campaigns for two structurally similar H-3 receptor antagonists. The first and second generation processes were developed for the synthesis of 107 and 125 g batches of (4-cyclobutyl-1,4-diazepan-1-yl)(6-(4-fluorophenoxy)pyridin-3-yl)methanone center dot HCl (1 center dot HCl). A third generation process was utilized for production of 104 g of 3-((5-(4-cyclobutyl-1,4-diazepane-1-carbonyl)pyridin-2-yl)oxy)benzonitrile center dot HCl (2 center dot HCl). The evolution from first to second generation process was driven by a desire to minimize cost of goods through employment of symmetrical homopiperazine rather than a more expensive monoprotected variant. Project demands for a late stage intermediate that could provide 1 or 2 led to additional route scouting and the ultimate determination of a third scalable synthesis for these types of molecules. The use of a lithium alkoxide for Lewis base catalysis of an ester to amide transformation represents a key improvement for the third generation synthesis.