1‐(4‐Methoxyphenyl)‐2‐(4′‐methylbenzylthio)ethylamine

[403739-55-9] C17H21NOS (MW 287.42) InChI = 1S/C17H21NOS/c1-13-3-5-14(6-4-13)11-20-12-17(18)15-7-9-16(19-2)10-8-15/h3-10,17H,11-12,18H2,1-2H3 InChIKey = MTYGTBRKASPSQE-UHFFFAOYSA-N (auxiliary used in the native chemical ligation of peptides and proteins) Form Supplied in: not commercially available. Preparative Methods: 1-(4-methoxyphenyl)-2-(4′-methylbenzylthio)ethylamine 3 was prepared in three steps from p-methoxy bromoacetophenone 1. Reaction with a suitable resin-bound bromoacetyl peptide,2 followed by S-deprotection gives the peptide 4, derivatized with the Nα-(1-(4-methoxyphenyl)-2-mercaptoethyl) auxiliary (eq 1). (1) The title compound 3 has been used in native chemical ligation (NCL) for the chemical synthesis of proteins.3-7 NCL selectively couples unprotected peptide segments to form larger polypeptides and proteins (up to ∼300 amino acid residues). The reaction occurs in aqueous systems at pH 7.0–7.2, and is chemoselective between an N-terminal cysteine peptide and a thioester. The thioester undergoes dynamic thiol exchange with the cysteine functionality (usually catalyzed by an aryl or alkyl thiol), which then rearranges “irreversibly” through a five-membered transition state to the native amide bond (eq 2). The chemoselectivity of this reaction arises from: 1. the protonation of other nucleophiles in the peptide at pH 7 (disfavoring undesirable acylation, e.g., at the γ-amino group of lysine residues); 2. the facile thioester exchange between COSR and the cysteine SH; and 3. the rapid rearrangement of the resulting α-amino thioester. This method has been combined with molecular biology techniques such as protein design and expression to expand the scope of proteins that can be synthesized and modified.8, 9 (2) One of the major limitations of the thioester-cysteine mediated ligation is the necessity for cysteine residues in the target molecule. Similar ligation strategies have been developed that exploit alternative acyl shifts between other functionality, e.g., the imidazole of histidine residues.5 However, the most general of these alternative strategies involves the use of removable ligation auxiliaries such as 3, which enable disconnection at a glycine residue. These auxiliaries provide an aryl or alkyl thiol α- or β- to an amine for thioester exchange and rearrangement to the amide. The use of auxiliary 3 offers several advantages over earlier systems, including rapid ligation rates and ease of removal postligation. The effectiveness of this auxiliary was first assessed using a model peptide of sequence Nα-(Aux)GlySerTyrArgPheLeu.1 This was successfully ligated with a number of thioester peptides, as illustrated below (eq 3), (Table 1), with post-ligation auxiliary removal achieved using either 95% HF/5% p-cresol or trifluoroacetic acid (TFA)/bromotrimethyl silane (TMSBr).10, 11 (3) Table 1. Ligation studies with auxiliary 3 Peptide-αCO-SR Reaction Time (h)a Ligation Yield (%)b Auxiliary Removal a Ligation conditions: 5 mM Nα-(Aux) peptide in 6 M guanidinium phosphate buffer pH 7, 25 °C, 2% thiophenol b Based on consumption of the Nα-(Aux) peptide. Thioester peptides were used in 1.5-fold excess. Phe-Gly-Gly 16 >98 HF Mouse Larc 1-31 (Ala) 40 92 HF MCP1 1–35 (Lys) 40 76 TFA/TMSBr