4A5S:
reference: Novel heterocyclic DPP-4 inhibitors for the treatment of type 2 diabetes., Sutton JM, Clark DE, Dunsdon SJ, Fenton G, Fillmore A, Harris NV, Higgs C, Hurley CA, Krintel SL, Mackenzie RE, Duttaroy A, Gangl E, Maniara W, Sedrani R, Namoto K, Ostermann N, Gerhartz B, Sirockin F, Trappe J, Hassiepen U, Baeschlin DK, Bioorg Med Chem Lett. 2012 Feb 1;22(3):1464-8. Epub 2011 Nov 20. PMID: 22177783

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