Boc and fmoc solid phase peptide synthesis

A method for preparing a peptide comprising three or more amino acid residues having an N-terminal amino acid, a next to last amino acid adjacent to the N-terminal amino acid and a C-terminal amino acid, wherein said method comprises the steps of:

• (a) attaching a first amino acid to a solid support resin through an ester bond to form a first-coupled-product, which comprises (i) reacting an aqueous solution of cesium carbonate with an alcohol solution of the first amino acid to form a cesium salt of the first amino acid, (ii) obtaining a solvent free cesium salt of the first amino acid, (iii) reacting the solid support resin with the cesium salt of the first amino acid in a dry polar aprotic solvent to form a first-coupled product;
• wherein the first amino acid corresponds to the C-terminal amino acid of the peptide, the first amino acid's non-side chain amino group is blocked by a Boc and the first amino acid does not have a side chain functionality requiring protection, and the solid support resin is a chloromethylated polystyrene resin;
• (b) deblocking the Boc from the first-coupled-product with an acid to form a first-deblocked-coupled-product;
• (c) optionally coupling a next-amino-acid to the first-deblocked-coupled-product, which comprises reacting the next-amino-acid with the first-deblocked-coupled-product in an organic solvent comprising a peptide coupling reagent to form a next-blocked-coupled-product, wherein the next-amino-acid has a non-side chain amino group blocked by Boc and if the next-amino-acid has one or more side chain functionalities then the side chain functionalities do not require protection or the side chain functionalities have protecting groups that are stable to acid and base reagents used to deblock Boc and Fmoc, respectively;
• (d) deblocking the Boc from the next-blocked-coupled-product which comprises reacting the next-blocked-coupled-product with a an acid to yield a next-deblocked-coupled-product;
• (e) optionally repeating steps (c) and (d), each cycle forming an (X+1)-next-deblocked-coupled-product where X is the number of desired cycle repetitions;
• (f) coupling a next-amino-acid to the first-deblocked-coupled-product from (b), or optionally to the (X+1)-next-deblocked-coupled-product from (e), which comprises reacting the next-amino-acid with said first-deblocked-coupled-product or said (X+1)-next-deblocked-coupled-product in an organic solvent comprising a peptide coupling reagent to form a next-blocked-coupled-product, wherein the next-amino-acid has a non-side chain amino group blocked by Fmoc, provided that if the next-amino-acid has one or more side chain functionalities then the side chain functionalities do not require protection or the side chain functionalities have protecting groups that are stable to base reagents used to deblock Fmoc;
• (g) deblocking the Fmoc from the next-blocked-coupled-product which comprises reacting the next-blocked-coupled-product with a primary or secondary amine to yield a next-deblocked-coupled-product;
• (h) optionally repeating steps (f) and (g), each cycle forming an (X+1)-next-deblocked-coupled-product where X is the desired number of cycle repetitions, until the next to last amino acid of the peptide is coupled and deblocked;
• (i) coupling an N-terminal amino acid to the (X+1)-next-deblocked-coupled-product, which comprises reacting the N-terminal amino acid with the (X+1)-next-deblocked-coupled-product in an organic solvent comprising a peptide coupling reagent to form a completed-blocked-coupled-product, wherein the N-terminal-amino-acid has a non-side chain amino group blocked by Boc or Fmoc;
• (j) deblocking the Boc or Fmoc group from the completed-blocked-coupled-product, which comprises reacting the completed-blocked-coupled-product with an acid in the case of Boc, or a base in the case Fmoc, to form a completed-peptide-resin-product;
• (k) if side-chain functionalities are present on the completed-peptide-resin-product then optionally deprotecting the side-chain functionalities of the completed-peptide-resin-product, which comprises reacting the completed-peptide-resin-product with the appropriate deprotecting reagents to form a deprotected-completed-peptide-resin-product;
• and
• (l) cleaving the peptide from the solid support resin of the completed-peptide-resin-product or the deprotected-completed-peptide-resin-product to yield the peptide, which comprises reacting the completed-peptide-resin-product or the deprotected-completed-peptide-resin-product with ammonia, a primary amine or a secondary amine until the cleavage of the peptide from the resin is substantially complete;
• provided that steps (f) and (g) must be carried out at least once in the synthesis of the peptide.