L-O-(2-malonyl)tyrosine: a new phosphotyrosyl mimetic for the preparation of Src homology 2 domain inhibitory peptides.

Inhibition of Src homology 2 (SH2) domain-binding interactions affords one potential means of modulating protein-tyrosine kinase-dependent signaling. Small phosphotyrosyl (pTyr)-containing peptides are able to bind to SH2 domains and compete with larger pTyr peptides or native pTyr-containing protein ligands. Such pTyr-containing peptides are limited in their utility as SH2 domain inhibitors in vivo due to their hydrolytic lability to protein-tyrosine phosphatases (PTPs) and the poor cellular penetration of the ionized phosphate moiety. An important aspect of SH2 domain inhibitor design is the creation of pTyr mimetics which are stable to PTPs and have reasonable bioavailability. To date, most PTP-resistant pTyr mimetics which bind to SH2 domains are phosphonates such as (phosphonomethyl)phenylalanine (Pmp, 2), [(monofluorophosphono)methyl]phenylalanine (FPmp, 3) or [(difluorophosphono)methyl]-phenylalanine (F2Pmp, 4). Herein we report the incorporation of a new non-phosphorus-containing pTyr mimetic, L-O-(2-malonyl)tyrosine (L-OMT, 5), into SH2 domain inhibitory peptides using the protected analogue L-N alpha-Fmoc-O'-(O",O"-di-tert-butyl-2-malonyl)tyrosine (6) and solid-phase peptide synthesis techniques. Five OMT-containing peptides were prepared against the following SH2 domains: the PI-3 kinase C-terminal p85 SH2 domain (Ac-D-(L-OMT)-V-P-M-L-amide, 10, IC50 = 14.2 microM), the Src SH2 domain (Ac-Q-(L-OMT)-E-E-I-P-amide, 11, IC50 = 25 microM, and Ac-Q-(L-OMT)-(L-OMT)-E-I-P-amide, 14, IC50 = 23 microM), the Grb2 SH2 domain (Ac-N-(L-OMT)-V-N-I-E-amide, 12, IC50 = 120 microM), and the N-terminal SH-PTP2 SH2 domain (Ac-L-N-(L-OMT)-I-D-L-D-L-V-amide, 13, IC50 = 22.0 microM). These results show that peptides 10, 11, 13, and 14 have reasonable affinity for their respective SH2 domains, with the IC50 value for the SH-PTP2 SH2 domain-directed peptide 13 being equivalent to that previously observed for the corresponding F2Pmp-containing peptide. OMT may afford a new structural starting point for the development of novel and useful SH2 domain inhibitors.