Na-Methyl amino acid residues are often found in microbial proteins which are synthesized by synthetases via N-methylation. These kinds of microbial compounds are normally of interesting pharmacological activities. Notable examples are Cyclosporin, Beauvericin, Enniatin and Dactinomycin.
Tips for using Na-methyl amino acids:
- Na-Methyl brings additional steric hindrance for coupling the next amino acid, which requires highly efficient activation of the carboxylic group for achieving better coupling result. HATU/HOAt or PyBrOP would be a better choice for coupling to Na-Methylated amino acids.
- Chloranil test may be not efficient to monitor the coupling effect since only week color may be observed with N-methylamino groups, while bromophenol blue test would do the work except for His-containing peptides.
- N-Methylated amine group may deprotect the Fmoc group of the next amino acid, which may make the coupling reaction sluggish. N-Silylation prior to the coupling helps to overcome the problem.
- Diketopiperazine formation and recemization may be more problematic with N-Methylated acids, therefore, reagents and conditions for suppressing Diketopiperazine formation and recemization should be employed. However, HOBt should be avoided since it also suppresses the coupling rate.
- N-Methylated peptide bonds are more acid-labile, mild conditions or limited time of treatment with TFA should be considered for cleavage of the peptides containing N-methyl amino acid residues.
Advanced ChemTech carries various Fmoc-N-methyl amino acids which would meet the needs of your peptides synthesis.