The Discovery of the Dipeptidyl Peptidase-4 (DPP4) Inhibitor Onglyza: From Concept to Market - Accounts in Drug Discovery Case Studies in Medicinal Chemistry - page 13

attribute of saxagliptin among the clinically advanced inhibitors. The slow off-
rate kinetics exhibited by saxagliptin likely serves to enhance saxagliptin's
pharmacodynamic potency and duration in vivo, and may also contribute to its
enzymatic selectivity. 47,48
Further understanding of this finding was obtained through: (1) a high-
resolution X-ray co-crystal structure of saxagliptin bound to DPP4, definitively
revealing the presence of a covalent O-C bond; (2) a series of biophysical
studies performed using wild-type and mutant DPP4 proteins S630A and
H740Q characterizing interactions with both saxagliptin and its de-nitrilo
analogue; and (3) comparative 1 H NMR studies of DPP4 in apo form and in
complex with saxagliptin, 45,49 revealing the characteristic downfield shift indi-
cative of a short, strong H-bond upon complex formation. 50,51 The X-ray co-
crystal structure of saxagliptin bound to DPP4 (Figure 1.9) reveals several key
features: (1) the ionic interaction of the primary amine with the Glu205 and
Glu206 residues; (2) hydrogen bonding of the adamantyl hydroxyl with Tyr547;
(3) ecient hydrophobic space-filling by the adamantyl and methano-pyrroli-
dine groups; and (4) the aforementioned covalent bonding of the catalytic
Ser630 hydroxyl with the pendant nitrilo functional group. Despite the clear
covalent nature of the bond, this interaction was shown to be fully reversible (as
demonstrated by complete recovery of enzyme activity upon dialysis) and
enzymatically unproductive (since no saxagliptin hydrolysis products were

Trp629

Asp780

His740

Asn710

Ser 630

Glu205

Tyr547

Glu206

Phe357

Figure 1.9 X-Ray co-crystal structure of saxagliptin bound to human DPP4.