Peptide fluoromethyl ketones

Fluoromethyl ketones are one of the most widely used classes of peptidyl a-fluoroalkyl ketones, second only to trifluoromethyl ketones. Peptidyl fluoromethyl ketones are very effective as irreversible inhibitors of cysteine proteases the first reported use of a fluoromethyl ketone compound was the use of Z-Phe-Ala-CH2F as an irreversible inhibitor of cathepsin BJ2,31 Today, many lysine and arginine derivatives have been synthesized as potential inhibitors for trypsin and trypsin-like enzymesJ3 There are four basic methods for the synthesis of peptide fluoromethyl ketones (1) the reaction of HF with peptide diazomethyl ketones (Section 15.1.4.1.1), (2) a halogen-exchange reaction with a chloro-, bromo-, or iodomethyl ketone (Section 15.1.4.1.2), (3) a Henry nitro-aldol condensation reaction (Section 15.1.4.1.3), and (4) a modified Dakin-West acylation reaction (Section 15.1.4.1.4). 

In this section the synthesis of fluoroalkyl (Section 15.1.4.1.3), a,a-difluoroalkyl (Section 15.1.4.2.3), and trifluoromethyl- and perfluoroalkyl ketones are discussed collectively. The second most widely used method for synthesizing peptide fluoromethyl ketones is the Henry nitro-aldol condensation reaction, which involves the use of (3-nitro alcohols to build the fluoromethyl ketones. As with the modified Dakin-West procedure, the Henry reaction has also been used to synthesize mono-, di-, tri-, and extended fluoromethyl ketones, making it another extremely versatile synthetic method.19 12 19 27 29 33 341 However, similar to the Dakin-West procedure, the products of the Henry reaction are not chiral, since an achiral carbanion is involved in the crucial carbon bond forming step. 

Peptide Fluoromethyl Ketones Fluoroalkyl derivatives of the peptide chloromethyl ketones have been prepared in an attempt to improve specificity by reducing nonspecific alkylation at cysteine residues (Rasnick, D., Synthesis of peptide fluoromethyl ketones and the inhibition of human cathepsin B, Anal. Biochem. 149, 461 65, 1985). Nonspecific reaction with sulfydryl groups such as those in glutathione was reduced there was still reaction with active site cysteine although at a slower rate than with the chloroalkyl derivative (16,200 M s vs. 45,300 1 2 21.9 min. vs. 

C-Terminal ketone derivatives of peptides have been used as effective inhibitors for a variety of proteases including serine, cysteine, and aspartyl proteases. 271 This class of peptides includes diazomethyl ketones (Section 15.1.2), halomethyl ketones (Section 15.1.3), and fluoromethyl ketones (Section 15.1.4). In general, the A -amino group and side chain must be protected. The diazomethyl ketones serve as good intermediates for conversion into chloromethyl and bromomethyl ketones. Fluoromethyl ketones, the most widely known class of peptide haloketones, can also be prepared from diazomethyl ketones or by halogen-exchange reactions. Other methods for the synthesis of fluoromethyl ketones are described in Section 15.1.4. 

Peptide Halomethyl Ketones (Excluding Fluoromethyl Ketones)... 

Peptidyl fluoromethyl ketones are widely used as fairly potent inhibitors for a variety of proteases, including serine, cysteine, and aspartyl proteases. Unlike other halomethyl ketones (Section 15.1.3), fluoromethyl ketones are reversible transition-state mimics. The electron-withdrawing fluorine(s) next to the carbonyl group enhances the electrophilicity of the a-fluoroalkyl ketone functionality, thereby making the carbonyl more susceptible to nucleophilic attack. a-Fluoroalkyl ketones are good mimics of peptide bonds due to the small size of the fluorine and the stability of C F bonds. There are three general classes of peptidyl fluoromethyl ketones fluoromethyl ketones (irreversible inhibitors of cysteine proteases), difluoromethyl ketones (reversible inhibitors of both serine and aspartyl proteases), and trifluoromethyl/perfluoroalkyl ketones, which typically exist in hydrated forms and are excellent inhibitors of both serine and cysteine proteasesJ1 ... 

Peptidyl fluoromethyl ketones can readily be synthesized by addition of organometallic reagents to peptide aldehydes and other carbonyl compounds 28 one variation of this reaction is suitable for the stereoselective synthesis of trifluoromethyl ketones. 23,31 ... 

Benzyloxycarbonyl-Val-Ala-Asp(OMe) fluoromethyl ketone (z-VAD-FMK) is a peptide halomethyl ketone used for the inhibition of caspases and related enzymes. Because z-VAD-FMK is neutral, it passes the cell membrane and can inhibit intracellular proteolysis and is useful in understanding the role of caspases and related enzymes in cellular function. See Zhu, H., Fearnhead, H.O., and Cohen, G.M., An ICE-like protease is a common mediator of apoptosis induced by diverse stimuli in human monocytes THP.l cells, FEBS Lett. 374, 303—308, 1995 Mirzoeva, O.K., Yaqoob, P., Knox,... 

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