Phosphonamide peptides

Phosphonamidate peptide analogues mimicking the P1...F3 substrate residues have been prepared and evaluated against a CHC mixture Table 8.5). Inhibitors with an aromatic side-chain in subsite P] are some 20-fold more effective than are those with an aliphatic one (compare (31) to (29) or (30), Table 8.S). An opposite, albeit less pronounced, preference at this site appears to exist for the ketone inhibitors for fi-CYlC ((17) vs. (25) and (21) vs. (26), Table 8.4). However, this difference could be attributable to a predominance of class II CHC in the mixture assayed in Table 8.5. Thus, comparisons of this sort must be made with caution. Introduction of a double bond into the Pi side-chain decreases the potency of the phosphonamidate by more than a factor of 10 ((41) vs. (42), Table 8.5), perhaps because of... 

Bartlett PA, Lamden LA. Inhibition of chymotrypsin by phos-phonate and phosphonamidate peptide analogs. Bioorg. Chem. 1986 14(4) 356-377. 

Figure 17.22. (a) Thermolysin-catalyzed hydrolysis of peptide analogs showing putative transition state, (b) phosphonamidate peptide analog, and (c) lluoroalkane peptide analog. 

Another motivation to use phosphorus-containing peptides is related to their good structural analogy with what is called the substrate structure in the transition-state. As shown in Fig. 3, three possibilities can be envisaged and have been explored to develop potent inhibitors. Phosphonamide peptides seem the most obvious choice, as the analogy is almost perfect [11, 12]. If such compounds have been proved to yield potent inhibitors towards some zinc-metalloproteases, the limited stability of the P-N bond through hydrolysis has prevented further use of this chemistry [13-15]. Phosphonates have been reported to yield one of the most potent inhibitor ever reported for carboxypeptidase A (Ki in the fM range) [13]. However, when tested with endoproteases, phosphonates turned out to be less potent [15]. 

Dheeman DS, Henehan GTM, Frias JM (2011) Purification and properties of Amycolatopsis mediterranei DSM 43304 lipase and its potential in flavour ester synthesis. Bioresour Technol 102 3373-3379 Dive V, Yiotakis A, Nicolaou A, Toma F (1990) Inhibition of Clostridium histolyticum collagenases by phosphonamide peptide inhibitors. Eur J Biochem 191 685-693... 

This approach has been mainly applied to peptide-based inhibitors of proteases, where the inhibitory molecule is a peptide with a transition state isostere appended to it, and the cognate substrate is simply a peptide of the same amino acid sequence, but lacking the isostere functionality. Examples where good correlations between the free energy of inhibitor binding and the free energy of kcJKM have been found, include peptide-trifluoromethyl ketone inhibitors of human leukocyte elastase (Stein et al., 1987) and peptide-phosphonamidate inhibitors of the metalloprotease ther-molysin (Bartlett and Marlowe, 1983). 

Phosphonate peptides can be synthesized either by formation of the P—O bond or the O—C bond. The former coupling is typically carried out via reaction of an alcohol (e.g., an a-hydroxy acid) with an activated phosphonyl spedes in a manner similar to phosphonamidate synthesis (Section 10.10.2.1). The latter process employs the phosphonate anion as a nucleophile in a displacement reaction on an ester with a leaving group in the a-position. 

The BOP- or PyBOP-mediated SPPS of phosphinot or phosphono peptides can be carried out without protecting the phosphinic or phosphonic acid group. Indeed, phosphinic acids are activated, but the P—N bond is not formed. Phosphonic acids are also acti-vatedt and in fact an amide of methyl phenylphosphonic acid has been obtained, however, in the case of protected a-amino phosphonic acids, phosphonamides are only obtained by using AT-phthalyl protection. Side-chain unprotected phosphorylated tyrosine [Tyr(P03H2)] can be coupled by solid-phase synthesis using BOP (PyBOP), but pyrophosphate formation is also observed and some particular Tyr(P)-peptide syntheses are prone to total failure. ... 

Bartlett and Marlowe (153) designed a series of five phosphonamidate analogs of the peptide carbobenzoxy-Gly-Leu-X (X = NH2, Gly, Phe, Ala, Leu), where a -POz-NH- replaces the Gly-Leu peptide bond, and showed that these compounds were potent transition-state analog inhibitors of the zinc endopeptidase thermolysin. They also synthesized the corresponding phos-phonate analogs, where the -NH- (13A) is replaced by -O- (I3B). The... 

Camp NP, Hawkins PCD, Hitchcock PB et al (1992) Synthesis of stereochemically defined phosphonamidate-containing peptides inhibitors for the HlV-1 proteinase. Bioorg Med Chem Lett 2 1047-1052... 

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