Problems associated with use of the benzyloxymethyl protecting group for histidines. Formaldehyde adducts formed during cleavage by hydrogen fluoride.
The use of N alpha-tert.-butyloxycarbonyl-N pi-benzyloxymethylhistidine in peptide synthesis resulted in significant levels of several different side products attributable to the generation of formaldehyde during the hydrogen fluoride cleavage reaction. Methylated impurities in a decapeptide were isolated and identified. These methylated impurities were attributed to the use of the benzyloxymethyl protecting group for the histidines, since the impurities did not form when the dinitrophenyl protecting group was used. Also, peptides containing benzyloxymethyl-protected histidines in addition to N-terminal cysteines quantitatively yielded their respective N-terminal thiazolidine derivatives upon isolation from standard hydrogen fluoride cleavage mixtures. Thiazolidine ring formation was circumvented by including in the cleavage reaction a formaldehyde scavenger such as cysteine hydrochloride or resorcinol.
Mitchell
M A
MA
Upjohn Company, Kalamazoo, Michigan.
Runge
T A
TA
Mathews
W R
WR
Ichhpurani
A K
AK
Harn
N K
NK
Dobrowolski
P J
PJ
Eckenrode
F M
FM
D000595:Amino Acid Sequence; D005557:Formaldehyde; D006639:Histidine / Q000031:analogs & derivatives*; D006858:Hydrofluoric Acid; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis*; D016339:Spectrometry, Mass, Fast Atom Bombardment
D007202:Indicators and Reagents; D010455:Peptides; D005557:Formaldehyde; D006639:Histidine; C068008:N(alpha)-tert-butyloxycarbonyl-N(pi)-benzyloxyhistidine; D006858:Hydrofluoric Acid