Solid phase peptide synthesis

Peptides were synthesized on the rink amide resin (0.6 mmol/g) on a Burrell Wrist-action shaker. 200 mg resin was treated twice (15 mins each time) with 3-mL 20% Piperidine in DMF to deprotect the Fmoc group. The beads were then washed twice with 3 mL each of DCM and DMF. The desired N-alloc protected γ-AApeptide building blocks were prepared (Fig. 8) and are combined (2 equivalents) with 4 equivalents each of HOBt and DIC in 3 mL DMF. The solution was then added to the deprotected resin and was allowed to react for 4 h. Ninhydrin test³⁸ was used to confirm the success of the coupling and depending on the Ninhydrin test result, a second round of coupling was done. On reaction completion, the beads were washed with DMF and DCM, followed by a fifteen minutes (15 min) capping reaction with 500 uL Acetic Acid. After capping, the beads were washed and alloc-deprotection reaction was done by reacting the beads with Pd (PPh₃)₄ (1 equivalent) and Me₂NH BH₃ (6 equivalents) (10 mins each time). The beads were then washed with DCM and DMF, followed by the reaction of the deprotected beads with acyl chloride (4 equivalents) and DIPEA (6 equivalents) in 3 mL DCM for 1 h or with the carboxylic acid (4 equivalents), HOBt (8 equivalents), and DIC (8 equivalents) for 6 h (x2).

Synthesis of γ-AApeptide building block/monomeric unit.

The above steps were repeated to assemble the desired sequence on the resin (Fig. 9). After these, the resin was washed and the peptide was cleaved from the resin with the cocktail: TFA/H2O/TIS (95/2.5/2.5) for 2.5 h. The solvent was evaporated to obtain the crude peptide, which was analysed and purified on an analytical (1 mL/min) and a preparative (20 mL/min) Waters HPLC system, respectively. 5–100% linear gradient of 0.1% TFA/ACN in 0.1% TFA/H2O over 50 min was used. The HPLC traces were detected at 215 nm. The products were confirmed by MALDI-TOF MS. The product fractions were then collected and lyophilized.

Solid Phase synthesis scheme for HW-155 and 1–8.