28
2 Synthesis of In-Tether Chiral Center Peptides …
FmocHN
OH
O
Me
FmocHN
OH
O
Ph
FmocHN
OH
O
Me
FmocHN
OH
O
Me
FmocHN
OH
O
FmocHN
OH
O
FmocHN
OH
O
Me
Ph
S 5 (2-Me)
S 5 (2-Ph)
S 4 (2-Me)
S 6 (2-Me)
S 5 (3-Me)
S 5 (3-Ph)
S 5 (5-Me)
Scheme 2.2 Chemical structures of nonnatural amino acids
Compound S3: Compound 2 (25.0 g, 0.065 mol), nickel (II) nitrate hexahydrate
(31.6 g, 0.11 mol) and glycine (20.5 g, 0.27 mol) were dissolved in anhydrous
methanol (300 ml) and heated to 50°C. The potassium hydroxide (25.0 g, 0.47 mol)
in methanol (150 ml) solution was added dropwise. After 10 h, acetic acid was
added. Methanol was removed and followed by pouring the residue liquid into ice
water (800 ml), and stirred at r.t. overnight to promote precipitation. The mixture was
filtered out under vacuum and residue was gathered to obtain red solid compound 3
(22 g, yield: 75%).
Compound S4: Under N 2 atmosphere, compound 3 (20.0 g, 0.04 mol) was
dissolved in DMF (200 ml), followed by the addition of powdered potassium
hydroxide (21.1 g, 0.4 mol) and the reaction mixture was stirred at r.t. for 1 h.
Under the condition of ice bath, 5-bromo-1-pentene (6 ml, 0.042 mol, J&K Co. Ltd)
was added dropwise. Then the reaction was gradually warmed to r.t. and stirred for
4 h before the addition of 5% v/v acetic acid in water. The reaction continued to be
stirred for 6 h to promote the precipitation and filtered out. The residue was gathered
and washed by water for three times to obtain compound 4 (23.2 g, yield: 87%).
Compound S5: Compound 4 (23.2 g, 0.035 mol) was dissolved in
methanol/CH 2 Cl 2 (v/v = 50 ml/100 ml), and 3 M hydrochloric acid (100 ml) was
added into the mixture. The reaction was heated to 80°C and stirred overnight until
yellow/green color change was observed. Then the solvent was removed in vacuo
and chloroform was used for extraction for three times to recover the ligand. The
amino acid aqueous fraction was used for the next step without further purification.
Compound S6: Sodium bicarbonate (16.8 g, 0.2 mol) and EDTA-Na (18.6 g,
0.05 mol) were added into the aqueous fraction to remove residual nickel. After stirring for 20 min, sodium bicarbonate was added again to make pH value of the mixture
stay at 7–8. Then the mixture was cooled to 0°C with ice bath. 9-fluorenylmethyl
succinimidyl carbonate (11.7 g, 0.035 mol) was dissolved in acetonitrile (25 ml)
and added dropwise into the aqueous solution. The reaction was gradually warmed
to r.t. and stirred for 12 h. Acetonitrile was removed in vacuo and citric acid was
2 Synthesis of In-Tether Chiral Center Peptides …
FmocHN
OH
O
Me
FmocHN
OH
O
Ph
FmocHN
OH
O
Me
FmocHN
OH
O
Me
FmocHN
OH
O
FmocHN
OH
O
FmocHN
OH
O
Me
Ph
S 5 (2-Me)
S 5 (2-Ph)
S 4 (2-Me)
S 6 (2-Me)
S 5 (3-Me)
S 5 (3-Ph)
S 5 (5-Me)
Scheme 2.2 Chemical structures of nonnatural amino acids
Compound S3: Compound 2 (25.0 g, 0.065 mol), nickel (II) nitrate hexahydrate
(31.6 g, 0.11 mol) and glycine (20.5 g, 0.27 mol) were dissolved in anhydrous
methanol (300 ml) and heated to 50°C. The potassium hydroxide (25.0 g, 0.47 mol)
in methanol (150 ml) solution was added dropwise. After 10 h, acetic acid was
added. Methanol was removed and followed by pouring the residue liquid into ice
water (800 ml), and stirred at r.t. overnight to promote precipitation. The mixture was
filtered out under vacuum and residue was gathered to obtain red solid compound 3
(22 g, yield: 75%).
Compound S4: Under N 2 atmosphere, compound 3 (20.0 g, 0.04 mol) was
dissolved in DMF (200 ml), followed by the addition of powdered potassium
hydroxide (21.1 g, 0.4 mol) and the reaction mixture was stirred at r.t. for 1 h.
Under the condition of ice bath, 5-bromo-1-pentene (6 ml, 0.042 mol, J&K Co. Ltd)
was added dropwise. Then the reaction was gradually warmed to r.t. and stirred for
4 h before the addition of 5% v/v acetic acid in water. The reaction continued to be
stirred for 6 h to promote the precipitation and filtered out. The residue was gathered
and washed by water for three times to obtain compound 4 (23.2 g, yield: 87%).
Compound S5: Compound 4 (23.2 g, 0.035 mol) was dissolved in
methanol/CH 2 Cl 2 (v/v = 50 ml/100 ml), and 3 M hydrochloric acid (100 ml) was
added into the mixture. The reaction was heated to 80°C and stirred overnight until
yellow/green color change was observed. Then the solvent was removed in vacuo
and chloroform was used for extraction for three times to recover the ligand. The
amino acid aqueous fraction was used for the next step without further purification.
Compound S6: Sodium bicarbonate (16.8 g, 0.2 mol) and EDTA-Na (18.6 g,
0.05 mol) were added into the aqueous fraction to remove residual nickel. After stirring for 20 min, sodium bicarbonate was added again to make pH value of the mixture
stay at 7–8. Then the mixture was cooled to 0°C with ice bath. 9-fluorenylmethyl
succinimidyl carbonate (11.7 g, 0.035 mol) was dissolved in acetonitrile (25 ml)
and added dropwise into the aqueous solution. The reaction was gradually warmed
to r.t. and stirred for 12 h. Acetonitrile was removed in vacuo and citric acid was