Mechanism-based isocoumarin inhibitors for human leukocyte elastase. Effect of the 7-amino substituent and 3-alkoxy group in 3-alkoxy-7-amino-4-chloroisocoumarins on inhibitory potency.

A series of 3-alkoxy-7-amino-4-chloroisocoumarins with various 3-alkoxy substituents have been prepared and evaluated as inhibitors of human leukocyte elastase (HLE). In addition, a new series of acyl, urea, and carbamate derivatives of 7-amino-4-chloro-3-methoxyisocoumarin (1), 7-amino-4-chloro-3-propoxyisocoumarin (3), and 7-amino-4-chloro-3-(2-bromoethoxy)isocoumarin (6) have been synthesized. Most of the synthesized compounds are very potent inhibitors of HLE with kobs/[I] values between 10(4) and 10(6) M-1 s-1. Hydrophobic substituents on the 7-amino position of the isocoumarin ring afford the best selectivity and inhibitory potency for HLE. In the 2-bromoethoxy series, compound 24 with a PhNHCONH 7-substituent had a kobs/[I] value of 1.2 x 10(6) M-1 s-1, was very selective for HLE, and was the most potent inhibitor of HLE tested. Of the extended chain L-phenylalanyl derivatives, the Bz-L-Phe compound 66 with a kobs/[I] value of 1.8 x 10(5) M-1 s-1 was the most potent inhibitor of HLE in the 3-methoxyisocoumarin series and was also very selective for HLE. Our results indicate that a high degree of selectivity, along with potency, can be introduced into mechanism-based isocoumarin inhibitors.

Dipeptide phosphonates as inhibitors of dipeptidyl peptidase IV.

A series of dipeptides which contained phosphonate analogs of proline and piperidine-2-carboxylic acid (homoproline) have been synthesized and tested as inhibitors of DPP-IV. The rates of inhibition of DPP-IV by these compounds are moderate, but the inhibitors are quite specific. The best inhibitor in the series is Ala-PipP(OPh-4-Cl)2 (13), which has a k(inact) of 0.353 s-1 and KI of 236 microM. The DPP-IV inhibitors Ala-ProP(OPh)2 (6), Ala-ProP(OPh-4-Cl)2 (12), and Ala-PipP(OPh-4-Cl)2 (13) do not inhibit trypsin, human leukocyte elastase (HLE), porcine pancreatic elastase (PPE), acetylcholinesterase, papain, and cathepsin B. However, compounds 12 and 13 inhibited chymotrypsin slowly. Most of these dipeptides containing a homoproline phosphonate residue (PipP) or a Pro phosphonate residue (ProP) at the P1 site are stable in a pH 7.8 buffer with half-lives of several hours to several days. DPP-IV inhibited by 6, 7 (Ala-PipP(OPh)2), 12, or 13 is quite stable, and no enzyme activity was recovered after removal of excess inhibitor and incubation in buffer for 1 day. Since the phosphonate inhibitors are specific toward DPP-IV and the inhibited enzymes are stable, they should be useful in establishing the biological functions of DPP-IV and may be useful therapeutically in the prevention of the rejection of transplanted tissue.