Somatostatin antagonists

Abstract

The present invention is directed to a method for synthesizing a peptide using solid-state chemistry in which at least one amide bond is N-methylated, wherein said method of synthesis utilizes N-Boc protected amino acids. For example, the a peptide is first synthesized using N-BOC protected amino acids and 4-methylbenzylhydrylamine functionalized 1% cross linked polystyrene resin until reaching the amide bond to be N-methylated. Then, the amino group at the desired methylation site is methylated. If desired, the synthesis of additional peptide using N-BOC protected amino acids may continued until the desired peptide is complete.

1 . A method for synthesizing a peptide using solid-state chemistry in which at least one amide bond is N-methylated, wherein said method of synthesis utilizes N-Boc protected ammo acids. 
     
     
         2 . A method according to  claim 1 , wherein said synthesis comprises the steps of:
 a) first synthesizing said peptide using N-BOC protected amino acids and 4-methylbenzylhydrylamine functionalized 1% cross linked polystyrene resin until reaching the amide bond to be N-methylated;   b) methylating the amino group at the desired methylation site; and, if necessary,   c) continuing synthesis of additional peptide using N-BOC protected amino acids until the desired peptide is complete.   
     
     
         3 . The method according to  claim 2  wherein said synthesizing comprises the steps of:
 a) deblocking said 4-methylbenzylhydrylamine functionalized 1% cross linked polystyrene resin;   b) first washing said deblocked resin;   c) neutralizing said washed resin;   d) second washing said neutralized resin;   e) double coupling said second-washed resin;   f) third washing said double coupled resin;   g) repeating steps a-f until reaching the amide bond to be N-methylated;   h) protecting the amino group at the desired methylation site;   i) methylating the amino group at the desired methylation site, and   j) deprotecting the methylated amide bond;   k) repeating steps a-g and a-j as necessary to complete the desired N-methylated peptide; and   l) cleaving said completed N-methylated peptide peptide from said resin.   
     
     
         4 . The method according to  claim 3  wherein:
 said deblocking is carried out in 40% TFA;   said first washing is carried out using three DCM washes;   said neutralizing is carried in 10% DIEA;   said second washing is carried out using one DMF wash followed by two DCM washes;   said double coupling is carried out wherein the first coupling uses 3 equivalents of 1,3-diisopropyl carbodiimide ester, followed by a DCM wash and the second coupling using 3 equivalents of preformed TBTU esters in the presence of DMF and DIEA; and   said third washing is carried out using a DMF wash followed by a DCM wash.   said protecting comprises
 a) resuspnding said third-washed resin in DCM; 
 b) mixing said resuspended resin in 3 equivalents of collidine and 3 equivalents of o-nitobenzenesulfonyl chloride; and 
 c) washing said mixed resin with DCM and DCF; and 
   said methylating comprises:
 a) resuspending said o-nitobenzenesulfonamide protected resin in DMF; 
 b) mixing said o-nitobenzenesulfonamide protected resin with 3 equivalents of MTBD and methyl 4-nitrobenzenesulfonate; and 
 c) washing said methylated resin with DMF; and 
   said deprotecting comprises:
 a) resuspending said methylated resin in DMF; 
 b) mixing said methylated resin with 3 equivalents of DBU and 3 equivalents of 2-mercaptoethanol; and 
 c) washing said deprotected resin with DMF.