The abbreviations for common aminoacids are those recommended by IUPACIUB Comission on Biochemical Nomenclature. Other abbreviations useful in
describing the replacements of aminoacids in the natural LH-RH peptide are
following:
Nal(2) - 3-(2-naphthyl)alanyl; p-Cl-Phe - 3-(p-chlorophenyl)alanyl; Pal(3) - 3-
(3-pyridyl)alanyl; ; hArg(Et)2 - NG,NG - bis(ethtyl)homoarginyl; Boc - tbutyloxycarbonyl.
Ganirelix (N-Ac-Nal(2)-D-pCl-Phe-D-Pal(3)-Ser-Tyr-D-hArg(Et)2-Leu-hArg(Et)2-
Pro-Ala-NH2) was prepared using the following side chain protection protocol:
salt protection for L- and D-hArg(Et)2 (as the chloride) and t-butyl protection
for serine.
Amino acids were added to the Nα-Boc-D-Ala-O-Resin (1.0 mmol of resin was
replaced in the reaction vessel of 5.0 L Vega 296 automated solid phase
peptide synthesizer; in the following sequence:
Acetic anhydride
An acetylation (capping of the resin) was done after Ala, Pro and Leu with
N,N'-diisopropyl carbodiimide - 1-hydroxybenztriazole (HBt). Excess HBt (2
equiv.) was used for the coupling of the basic amino acids, hArg(Et)2 and
Pal(3).
The following protocols were used to remove the Nα-protecting group following
each addition.
Program A: The resin was first washed with CH2Cl2 1 times/1 min, TFA-CH2Cl2
(40/60) 1 times/1 min, TFA-CH2Cl2 (40/60) 1 times/30 min, CH2Cl2 2 5
times/1 min, Et3N-CH2Cl2 (5/95) 3 times/1 min, CH2Cl2 4 times/1 min.
Program B: The resin was first washed with CH2Cl2 1 times/1 min, 4-4.5 N
HCl in CH2Cl2/i-PrOH (1/1) 1 times/1 min, 4-4.5 N HCl in CH2Cl2/i-PrOH (1/1)
1 times/30 min, CH2Cl2 3 times/1 min, DMF 1 times/1 min, Et3N-CH2Cl2
(5/95) 3 times/1 min, DMF 1 times/1 min, CH2Cl2 4 times/1 min.
After each deprotecting and washing step, following protocol A or B, the next
amino acid in sequence was added and the resin washed with CH2Cl2 3
times/1 min, MeOH 4 times/1 min, DMF 2 times/1 min and CH2Cl2 4 times/1
min.
Program A was used for the removal of the protecting groups on Ala, Pro, LhArg(Et)2, Leu and D-Nal(2).
Program B was used for the removal of the protecting groups on D-hArg(Et)2,
Tyr, Ser, D-Pal(3) and p-Cl-Phe.
The crude peptide was first dissolved in 2 M acetic acid and converted to its acetate salt by passage through a column of AG3-X4A resin (Bio-Rad). The
acetate was subjected to chromatography on a silica gel column (CH2Cl2/iPrOH/MeOH/H2O/HOAc solvent); the acetate fractions dissolved in H2O and
loaded onto a reversed-phase column (Vydec C-18, 15-20 μ), and purified
using acetonitrile/TEAP (pH 3). Fractions of the desired purity were combined
and diluted with water and reloaded on a reversed-phase HPLC column, then
washed with 1% acetic acid in water. The peptide was stripped with a mixture
of MeOH/CH3CN/HOAc/H2O (44/50/1/5). The residue was dissolved in acetic
acid and precipitated over ether, filtered, washed with ether and dried under
vacuum. Amino acid analyses were performed on a Beckman 119CL amino
acid analyzer. Samples for amino acid analyses were hydrolyzed with 6 N HCl
at 110°C for 20 hrs. Analytical HPLC was performed on a Spectra Physics
8800 chromatograph. Synthesis of ganirelix was confirmed by the presence of
a main peak at rt 18 min; no other peak over 1% was noted at rt 16 min.
