Ketones fluoromethyl

The synthesis of fluoroalkyl and chloroalkyl fluoromethyl ketones is achieved by oxidation of the corresponding alcohols by sodium dichromate and sulfunc acid in methylene chlonde in the presence of a phase transfer catalyst [49] (equation 45)... 

Treatment of a-dichloromethyl phenyl sulfoxide with lithium diisopropylamide in THF gave monolithiated derivative 122, which upon further treatment with aldehyde afforded the )S-hydroxy-a-dichlorosulfoxide 123. Thermolysis of 123 gave dichloroketone 124, by extruding benzenesulfenic acid as shown below . Similarly, in the reaction of lithio-a-fluoromethyl phenyl sulfoxide and aldehyde, fluoromethyl ketone 126 was obtained, after thermolysis of the hydroxy intermediate 125. Diethylphosphorylmethyl methyl sulfoxide was shown by Miko/ajczyk and coworkers to be lithiated with n-BuLi to intermediate 127, which upon treatment with carbonyl compounds afforded the corresponding a, -unsaturated sulfoxides 128 in good yields. 

Fluoromethyl ketone 72 is obtained diastereomcrically pure by the Claisen rearrangement of (Z.Z)-ether 71 as a key step in the synthesis of a fluoro analog of the mycotoxin botryodi-plodin.25 No acceleration due to the presence of fluorine is observed in what is nevertheless a high-yield, stereoselective transformation. 

The epoxide-ketone rearrangement is not limited to polyfluorooxiranes. Michel and Schlosser have studied the isomerization of 2-fluorooxiranes to oc-fluoro ketones by the action of triethylamine trishydrofluoride.47 Thus, 2-substituted 2-fluorooxiranes 10 isomerize re-giosclectively to fluoromethyl ketones 11 when heated at 125 C. 

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 ... 

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). 

Table 1 Fluoromethyl Ketones by Reaction of Hydrogen Fluoride/Pyridine with Diazomethyl Ketones1 44 1...

Scheme 2 Synthesis of a Fluoromethyl Ketone via a Halogen-Exchange Reaction 7- 1...

The Henry nitro-aldol condensation involves the use of P-amino alcohols as the building blocks of fluoromethyl ketones. Although this method has been used extensively in the synthesis of monofluoropeptides (Table 2),19-121 it is more widely utilized as a method for synthesizing trifluoromethyl ketones and the details of the reaction will be discussed in Section 15.1.4.3.2. 

Table 2 Fluoromethyl Ketones Synthesized via the Henry Nitro-Aldol Condensation1912 ...

As with the Henry nitro-aldol condensation, the modified Dakin-West acylation is primarily used for synthesis of trifluoromethyl ketones, although there are several examples of its use in the synthesis of fluoromethyl ketones (Table 3).[31314 The modified Dakin-West reaction utilizes fluoroacetic anhydride (or other appropriate anhydrides) to form an anhydride, which then undergoes cyclization, activation of the a-carbon, and acylation at the a-carbon the precise details of this method will be discussed in Section 15.1.4.3.1. 

Table 3 Fluoromethyl Ketones Synthesized by the Modified Dakin-West Acylation1313 ...

One of the most widely used methods for the synthesis of peptidyl fluoromethyl ketones is a modified Dakin-West acylation procedure. Although this reaction is primarily used for the synthesis of trifluoromethyl ketones (see Scheme 4), it is also frequently used to synthesize fluoroalkyl (Section 15.1.4.1.4), difluoroalkyl (Section 15.1.4.2.2), and perfluoroalkyl ketones. This method is extremely versatile however, there are several drawbacks. First, as noted in Section 15.1.4.1.2, several of the reagents used in the Dakin-West acylation are... 

Scheme 4 Synthesis of Fluoromethyl Ketones by a Modified Dakin-West Reaction 20 ...

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. 

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 ... 

The condensation-cyclization of fluoromethyl ketones with bifunctional aniline derivatives or anthranilic acid gives a range of fluorinated heterocycles (benzimida-zolines, benzothiazolines, benzoxazolines and dihydrobenzoxazinones) over Nafion-H and Nafion SAC-13 both exhibiting high catalytic activity.722 Products are formed under mild conditions in high yields with high selectivity and purity. Illustrative is the transformation shown in Eq. (5.271). 

L-Proline catalyses direct aldols of trifluoroacetaldehyde ethyl (hemi)acetals, F3C-CFl(OH)-OX (X = H, CH2CH3, CH2CF3), with ketones at room temperature to produce /Miydroxy-/9-fluoromethylated ketones with des up to 96% and ees up to 91 %.97... 

Shaw E, Angliker H, Rauber P et al (1986) Peptidyl fluoromethyl ketones as thiol protease inhibitors. Biomed Biochim Acta 45 1397-1403... 

In contrast to basic protodesilylation, the use of sulfuric acid leads to fluoromethyl ketones 19 by hydration of the intermediate difluoroalkenes. ... 

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. 

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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