Proteasome vinyl sulfones

Scheme 14 Modification of proteasome threonine with vinyl sulfone ABPP probe...

Modifications of this approach have led to ABPP probes that are capable of selectively labeling the pi and p5 subunits of the proteasome [138]. In further studies of the proteasome, bifunctional ABPP probes containing a vinyl sulfone linked to a photoreactive moiety allows photocrosslinking of subunits adjacent to proteasomal catalytic sites [139]. 

Fig. 9 Structures of compounds used to compare the photoaffinity labeling of different photoreactive groups, (a) Photoreactive dUTP analogs 84a-d reported by Tate et al. [87]. (b) Photoreactive SAH analogs 85a,b reported by Dalhoff et al. [88]. The insert shows the transfer of the activated methyl group from SAM to nucleophilic positions (Nu) in various substrates by methyltransferases (MTase). A adenosine, (c) Photoreactive metalloprotease probes 86a,b reported by Yao et al. [65]. (d) Diazirine-containing analog of clicked compound 79-80 for labeling of y-secretase, reported by Fuwa et al. [82], (e) Photoreactive peptide vinyl sulfones 88a-c used to probe the 20S proteasome cavity, reported by Geurink et al. [89]...

Peptide vinyl sulfones are synthetic irreversible proteasome inhibitors that covalently modify its catalytic / subunits [47]. They are easier to synthesize than other irreversible proteasome inhibitors, and they do not inhibit serine proteases. 

Figure 10 Cell-permeable peptidomimetic vinyl sulfone probe for the labeling of proteasomal subunits.

See Rydzewski, R.M., et al. Optimization of subsite binding to the (35 subunit of the human 20S proteasome using vinyl sulfones and 2-Keto-l,3,4-oxadiazoles Synthesis and cellular properties of potent, selective proteasome inhibitors. J. Med. Chem. 2006, 49, 2953-2968. 

Further analyses of JAKl expression in HCMV-infected cells revealed that JAKl levels are decreased posttranslationally by a subset of HCMV genes. Steady-state JAKl mRNA levels are not altered in the course of HCMV infection despite decreased JAKl protein at 48 and 72h after infection (Miller et al. 1998). Moreover, treatment of HCMV-infected cells with carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone (Z-L3VS), a specific inhibitor of the proteasome, reverses the decrease of JAKl protein in HCMV-infected cells, suggesting that JAKl protein... 

In recent years, a number of structurally distinct compounds targeting the proteasome have reached the clinic, amongst others the covalent and irreversible inhibitor carfilzomib [5]. The structure of carfilzomib is based on that of the natural product, epoxomicin, that also features the epoxyketone electrophilic trap. Indeed, numerous natural product proteasome inhibitors with a distinguishing electrophile grafted onto a peptidic core have been described over the years, including lactacystin, syringolin A (SylA), and fellutamide B. An important class of synthetic covalent proteasome inhibitors is represented by the peptide vinyl sulfones, whereas numerous noncovalent proteasome inhibitors have been discovered as well (e.g., TMC 95A). 

Most of the proteasome ABPs reported are based on either peptide vinyl sulfones or peptide epoxyketones. In Figure 12.3a, the mechanism by which N-terminal threonines within proteasome active sites catalyze peptide bond hydrolysis is depicted. Aligning of either a vinyl sulfone or an epoxyketone at the appropriate position (i.e., the carbonyl of the scissile amide bond) allows covalent and irreversible reaction with the N-terminal threonine-OH (and -NH2 in case of epoxyketones) (Figure 12.3b) and therefore employment of these electrophiles in ABP design. Of the two electrophiles, especially the epoxyketone - evolved in nature - is an intriguing electrophilic trap it presents two electrophilic carbons to the 1,2-aminoalcohol characteristic and almost unique for proteasome active sites. 

Figure 12.3 Peptide vinyl sulfones and peptide epoxyketones in activity-based proteasome profiling, (a) Catalytic mechanism of proteasome-mediated peptide bond cleavage, (b) Covalent adducts of protea-somes reacting with vinyl sulfones and...

A protocol for proteasome labeling in vitro and in situ with broad-spectrum biotin-or Bodipy-containing peptide vinyl sulfones or peptide epoxyketones. 

Like bortezomib, MLN9708 is also a peptide boronate (Fig. 13.5) but it is orally active, shows greater tissue penetration, and has a shorter half-hfe. The drug is primarily an inhibitor of the chymotrypsin-like activity of the 20S proteasome core and, like bortezomib, it inhibits NF-kB activation and has antitumor activity in multiple myeloma and some other hematologic mahgnan-cies. Besides peptide boronates like bortezomib, other synthetic compounds tested as proteasome inhibitors include peptide aldehydes, peptide epoxyketones, and peptide vinyl sulfones. 

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