Optimization of peptidyl allyl sulfones as clan CA cysteine protease inhibitors

Figures & data

Figure 1.  Basic scaffold of dipeptidyl allyl sulfone inhibitors with enzyme subsite designations P3, P2, P1 and P1′.

Scheme 1.  (a) EDCl, HOBT, Et₃N, DCM, overnight; (b) iBCF, NMM, THF/DMF, overnight; (c) 1 eq.n-BuLi, 4.5 eq. t-BuOOH, −20°C for 70 min, 9 h or 18 h.

Scheme 2.  Isomerization equilibrium and elimination mechanism.

Figure 2.  Energy minimized models of the E and Z isomers of Mu-Phe-Hfe-AS-Ph.

Table 1.  Quantification of relative NOE magnitude and the deduced stereochemistry.

Compound	Structure	Vinyl sulfone precursor	Normalized NOE	Configuration
14	Mu-Phe-Hfe-AS-Ph	Mu-Phe-L-Hfe-VS-Ph	0.688	E
15	Mu-Phe-Hfe-AS-Ph	Mu-Phe-D-Hfe-VS-Ph	1.00	Z
18	Mp-Phe-Hfe-AS-Ph	Mp-Phe-L-Hfe-VS-Ph	0.749	E
19	Mp-Phe-Hfe-AS-Ph	Mp-Phe-D-Hfe-VS-Ph	1.00	Z

Figure 3.  NOESY comparison of 14 (blue) and 15 (red).

Table 2.  Inhibitor potencies for proteases.

Compound	Inhibitor	kobs/[I] (M^−1s^−1)			Trypsin
		Cathepsin B	Cruzain	Calpain I
14	E-Mu-Phe-Hfe-AS-Ph	420 ± 110	6080 ± 1390	<10	NI
15	Z-Mu-Phe-Hfe-AS-Ph	<10	260 ± 80	<10	NI
16	Cbz-Phe-Phe-AS-Ph (isomer A)	NS	NS	NS	NS
17	Cbz-Phe-Phe-AS-Ph (isomer B)	NS	NS	NS	NS
18	E-Mp-Phe-Hfe-AS-Ph	570 ± 20	2310 ± 230	<10	NI
19	Z-Mp-Phe-Hfe-AS-Ph	200 ± 40	130 ± 10	<10	NI
20	Mp-Phe-Phe-AS-Ph (isomer A)	13 ± 1	45 ± 1	<10	NI
21	Mu-Phe-Hfe-Elim	< 10	< 10	<10	NI

NS, not soluble; NI, no inhibition.

isomer A = from L-P1 vinyl sulfone residues, isomer B = from D-P1 vinyl sulfone residue.

Scheme 3.  Potential mechanisms of inhibition.