Regioselective Formation of Multiple Disulfide Bonds with the Aid of Postsynthetic S-Tritylation

Abstract

Disulfide bond formation performed in solution with the tert-butylthio (StBu) group was accomplished using a free peptide having only the sulfhydryl groups of Cys protected with the aid of postsynthetic S-tritylation. This facilitated removal of the StBu group with subsequent disulfide formation without any difficulty. This strategy using the StBu group in combination with the widely used acetamidomethyl (Acm), 4-methylbenzyl/4-methoxybenzyl (Meb/Mob), and trityl (Trt) groups enables reliable and regioselective synthesis of multicystine peptides.

Stepwise Construction of Disulfides in Peptides

“…In addition to the post‐SPPS exchange of thiol‐protecting groups, post‐SPPS S‐tritylation has been developed to add an additional level of chemical orthogonality to the existing Fmoc‐Cys thiol protecting‐group schemes (Figure ) . This advance enables solution‐phase disulfide formation between two S−S t Bu groups.…”

Palladium‐Mediated Direct Disulfide Bond Formation in Proteins Containing S‐Acetamidomethyl‐cysteine under Aqueous Conditions

“…The first one relies on subjecting the reduced peptide to freely oxidative folding conditions using a buffer containing redox reagents (e.g., Cys/Cystine) to form the correct connectivity under thermodynamic control ,,. The main limitations of this approach are the slow rate of the reaction (hours–days) and the requirement for careful optimization of the desired ratio between the redox reagents for each system …”

“…The second approach is based on regioselective disulfide bond formation through stepwise oxidation by employing various orthogonal Cys protecting groups (PGs) such as the S‐acetamidomethyl (Acm) and the tert ‐butyl (t ‐butyl) . Although this approach has enabled the chemical syntheses of various interesting peptides and proteins (e.g., insulin), the harsh removal conditions for the Cys PGs significantly reduce the efficiency of this approach . For example, a widely used method to convert two Cys(Acm) residues into the corresponding disulfide is based on iodine oxidation in acetic acid, however, over‐oxidation of the thiol functionality to sulfonic acid could occur, and other side reactions have been reported when Tyr, Trp, and Met are present…”

GAP Peptide Synthesis through the Design of a GAP Protecting Group: An Fmoc/tBu Synthesis of Thymopentin Free from Polymers, Chromatography and Recrystallization

“…31 169.9, 156.4, 143.9, 141.4, 139.3, 132.9, 132.6, 132.2, 132.1, 131.8, 128.7, 128.6, 128.1, 128.0, 127.9, 127.2, 125.2, 120.1, 67.4, 66.4, 47.2, 42.9 ppm. 31 (d,J = 7.6 Hz,2 H),6 H),J = 7.4 Hz,4 H),4 H),4 H),J = 7.4 Hz, 2 H), 6.95-6.93 (d, J = 8.4 Hz, 2 H), 6.87-6.85 (d, J = 8.4 Hz, 2 H), 5.28-5.26 (d, J = 7.9 Hz, 1 H), J = 8.5 Hz,2 H),1 H),2 H),J = 6.9 Hz, 1 H), 3.09-3.06 (m, 2 H), 1.30 (s, 9 H) ppm. 13 C NMR (100 MHz, CDCl 3 ): δ = 171.…”

“…[4] Developed by Merrifield in the 1960’s, Solid-Phase Peptide Synthesis (SPPS) has become a standard protocol used by multiple scientific disciplines for research and manufacturing. [5] The advantages of the polymer support lie in its ability to allow facile purification of the growing peptide after each coupling/deprotection step, which avoids the use of column chromatography.…”