The Desigin, Synthesis And In Vitro Activity Studies Of Pyrrolidine And Fuse Pyrazine Derivatives As Potential Dipeptidyl Peptidase Ⅳ Inhibitors

As new oral drugs for treatment of type 2 diabetes patients, pyrrolidine and fuse pyrazine derivatives often exhibit good DPP IV inhibiting activity. Therefore, structural extending and optimizing based on those DPP IV inhibitors are significant from both research and application.According with the general method of drug discovering, some drug-like function groups were introduced into the active molecular skeleton. Two series of pyrrolidine and fuse pyrazine derivatives had been designed, synthesized and bioassayed.Adopting the structural motif of pyrrolidine derivatives,16 new pyrrolidine analogues were designed, synthesized and evaluated for inhibiting activity toward DPP IV enzyme. All of the compounds were characterized by'H NMR and MS. By modifying the pyrrolidine structure with branched-chain extension, introduction of the pyrazine function and adoption of acyl, sulfonyl or aryl at 4-position of pyrazine, ten derivatives with the functional cyano group were synthesized. Six CN-deficient analogues in which the cyano group was replaced by an electron-withdrawing hetrocycle were also synthesized. It was found that two of the target compounds, MB-2 (70%) and MB-5 (34%) exhibited certain inhibiting activity toward DPP IV enzyme at the concentration of 20μg/mL. In general, the in vitro inhibiting activities of those compounds were quite low.By structural optimization on P1 and P2 pieces of a typical fuse pyrazine DPP IV inhibitor respectively,29 fuse pyrazine derivatives were designed, synthesized. The structures of all compounds were confirmed by 1H NMR,13C NMR, and MS or HRMS. The inhibiting activity of the target compounds toward DPP IV enzyme was also evaluated. Detailed works including:1) By introducing a a-amino acid or aβ-amino acid with diphenyl group in P2 piece, five fuse pyrazine analogues were synthesized and evaluated. It was found that the target compounds did not show any positive action against DPP IV enzyme.2) The P1 piece of fuse pyrazine derivatives was optimized step by step. Firstly, three analogues were prepared by replacing the heterocycles in P1 piece with different isosteres of triazolopyrazine. It was found that imidazopyrazine derivative MB-22 exhibited no inhibiting activity. Oxazolopyrazinone derivative MB-23 and imidazopyrazinone derivative MB-24 showed certain inhibiting activity against the enzyme. MB-24 provided about 2-fold increase in inhibitory potency toward DPP IV enzyme over MB-23. Secondly, the adoption of alkyl or benzyl substitutions at the 2-position of imidazopyrazinone heterocycle resulted in the discovery of derivative MB-27 (IC50=150 nM) which was regarded as a significant lead. Thirdly, subsequent optimization of leading compound MB-27 was performed by introducing different groups such as F, Cl, Me, MeO or CN into the 3-or 4-position of the benzyl group of MB-27. All analogues showed lower activity than MB-27. Fourthly, one methoxyl group at the 2-or 3-position, or two methoxyl groups at 3-and 5-position were then introduced to the benzyl group of MB-27. The enzyme-inhibited activity was insensitive to the number as well as the substituted position of MeOs. Fifthly, when a-CONH2 was introduced to the 3-position of benzyl, compound MB-37 (IC50=78 nM) with excellent DPP IV enzyme inhibited activity was obtained. Sixthly, by introducing aryl functional groups into the 2-position of the benzyl group of imidazopyrazinone,8 analogues were synthesized and evaluated. No in vitro activity against DPP IV enzyme was observed.To investigate the binding mode of the target compounds with DPP IV enzyme, molecular docking studies on both compound MB-25 which exhibited only weak enzyme inhibited activity, and the higher active compound MB-37 were performed by using sybyl 7.0. It was demonstrated that both (8aR) and (8aS) MB-25 exhibited weak interactions with the active site of DPP IV The introduction of carboxyl and benzyl groups to the fused piperazine remarkably improves the binding capacity with DPP IV enzyme. One of the optical isomers of MB-37, (8aS) MB-37, showed better interactions with the active site of DPP IV over (8aR) MB-37 with an additional H-bond. Further investigation of (8aS) MB-37 is earring through in our lab.