Process incorporating catalytic asymmetric hydrogenation for the preparation of sitagliptin.
One means for eliminating steps is to avoid the use of protecting groups, effectively removing two steps required to protect the starting material and subsequently deprotect the product. Such an idea was incorporated into the second generation synthesis of sitagliptin. The asymmetric hydrogenation of an enamine would be a more efficient means to synthesize the β-amino acid moiety, but a significant drawback was the requirement of an acyl protecting group on the nitrogen atom. This group is usually considered indispensable for chelation between the reactant and the metal catalyst in order to lead to high reactivity and selectivity.