u2014 oh boc met u2014 oh boc gln u2014 oh boc ile u2014 oh boc lys 2clz u2014 oh boc ser bzl u2014 oh and boc trp fm u2014 oh the synthesis was carried out on a 0 14 mmol scale the boc groups were removed by treatment with 100 tfa for 2 u00d7 1 min box amino acids 2 5 mmol were pre activated with hbtu 2 1 mmol and diea 1 0 ml n 4 ml of dmf and were coupled without prior neutralization of the peptide resin tfa salt coupling times were 5 min except for the boc aib u2014 oh and the following residue boc asn xan u2014 oh wherein the coupling times were 20 min at the end of the assembly of the peptide chain the resin was treated with a solution of 20 mercaptoethanol 10 diea in dmf for 2 u00d7 30 min to remove the dnp group on the his side chain the n terminal boc group was then removed by treatment with 100 tfa for 2 u00d7 2 min after neutralization of the peptide resin with 10 diea in dmf 1 u00d7 1 min the formyl group on the side chain of trp was removed by treatment with a solution of 15 ethanolamine 15 water 70 dmf for 2 u00d7 30 min the.