Show the steps and intermediates in the synthesis of Leu-Ala-Phe by the solid-phase process.

In solid phase peptide synthesis, the peptide is immobilized on a solid support (resin) and the intermediates are not isolated. This process does not require purification or analytical characterization. The resin-bound peptide remains isolated during the synthesis phase and following each reaction, that is couplings and deprotections, excess reagents and solvents can be easily washed away with repeated solvent washes.

Fmoc is a N-protecting reagent used here and in the first step, the C-terminus of N-protected amino acid that is, Fmoc-phenylalanine is attached to the polymer support. Then, for deprotection of N-terminus, piperidine in DMF is added and in next step, Fmoc-alanine gets added which couples with phenylalanine amino acid which is attached to polymer support. DCC is a coupling reagent used here.

Then, piperidine deprotects the N-terminus which further on treatment with Fmoc-leucine undergoes coupling in presence of DCC which gives rise to N-terminus protected peptide chain consisting of Leu-Ala-Phe in which phenylalanine is attached to a polymer support. Then, in last step, hydrogen fluoride is added which deprotects the N-terminus and removes the polymer and we get the required peptide.

Solid phase synthesis of Leu-Ala-Phe