Pepstatin synthesis

We synthesized the ketomethylene, , and hydroxyethylene,8, isosteres of a Leu-Ala dipeptide sequence in order to explore the importance of the two extra atoms in statine relative either to substrate or to the tetrahedral intermediate (Figure 1) in another aspartyl protease system. The compounds were synthesized by the routes outlined in Scheme I. This route was chosen so as to provide steric control at C-2 and C-5 of both 7 and 8 as well as to provide ready access to C-4 labeled analogs. Details of the synthesis have been described else-where.(23.24) Inhibitors were synthesized in which Leu-Ala dipeptide Isosteres replaced either Sta or Sta-Ala in known pepstatin analogs. Inhibition of porcine pepsin was determined using the reported spectrophotometric assay (Table I).(25)... 

The statine residue mimics the noncovalently bonded tetrahedral intermediate, permitting formation of a very tight complex. Pepstatin is a poor inhibitor of human renin but its existence has inspired the synthesis of numerous related compounds, some of which are effective renin inhibitors/ Some of these inhibitors use the human angiotensinogen sequence with a secondary alcohol group mimicking the tetrahedral intermediate/ 2... 

Kratzel, M., Hiessbock, R., and Bernkop-Schniirch, A. Auxiliary agents for the peroral administration of peptide and protein drugs Synthesis and evaluation of novel pepstatin analogues. J. Med. Chem. 41 2339—2344, 1998. 

Nonapeptide hnear amides are also often synthesized using the carbodiimide method. Examples include the synthesis of norcardicine A and the synthesis of renin inhibitors. The total synthesis of a trifluoromethyl (Tfm) analogue of pepstatin uses EDCCl/HOBt in the condensation steps. ... 

Rich DH, Bernatowicz MS. Synthesis of analogues of the carboxyl protease inhibitor pepstatin. Effect of structure in subsite P3 on inhibition of pepsin. J. Med. Chem. 1982 25 791-795. 

The reductive defluorination-alkylation method shown in Scheme 10.12 was successfully applied to the synthesis of A -Boc-Sta-xF[CF=CH]-Ala ethyl ester 51, which mimics the central Sta-Ala unit of pepstatin, a naturally occurring inhibitor of aspartyl proteases including renin, pepsin, HIV-1 and HIV-2 proteases (see Figure 10.3) [27]. 

Two different approaches to ( —)-statine (831), an unusual amino acid component of pepstatine, both employ 793c as their starting point. In the first synthesis (Scheme 120) [183], reduction of 793c with sodium borohydride produces a mixture of two isomeric 5-hydroxy-pyrrolidinones, from which the pure cis product 824 crystallizes in 85% yield. Conversion of bisacetate 825 to thioether 826 followed by removal of the acetate and silylation of the resulting alcohol affords 827. Radical cyclization of 827 produces a 3 2 mixture of isomers 828. Desilylation and debenzylation gives 829 as a single diastereomer. The Boc-protected intermediate 830 intersects with a known synthesis of ( —)-statine (831). 

CgH NOj, Mr 175.23, mp. 201-203°C (decomp.), [o] -20 (H2O). An amino acid in pepstatin A, a pentapeptide mixture and inhibitor of the protease pepsin produced by various Streptomyces species. S. and its derivatives are of major importance in the synthesis of pseudopeptidic protease inhibitors as therapeutics for hypertension (as renin inhibitors) and AIDS (as HIV protease inhibitors). 

Interestingly, it was reported that the synthesis of Fe(C5H4-CO-Pro,-OBn)2 with n= 2,3 or4, yielded a second class of compounds, i.e. the incomplete substituted derivatives Fe(C5H4-CO-Pro,j-OBn)(C5H4-CO-OBt) [26]. In a subsequent paper, Kraatz and coworkers reacted the incompletely substituted derivatives with n = 3 and 4 with a pepstatin analog to obtain the conjugates shown in Scheme 5.6 [28]. 

D. H. Rich, E. Sun and J. Singh, University of Wisconsin, Madison, Synthesis of Dideoxy-Pepstatin, Mechanism of Inhibition of Porcine Pepsin . 

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