1644
P. D’Arrigo et al. / Tetrahedron: Asymmetry 20 (2009) 1641–1645
1.42 (s, 9H); ½a 2D4
ꢀ
¼ þ10:1 (c 1.01, CHCl3); ESI/MS: [M+H]+ = 221.9
conversion of substrates. After the reaction was completed, the en-
[M+Na]+ = 243.9.
zyme was filtered off and the solvent was evaporated under vac-
uum. The obtained residue was purified by chromatographic
column using hexane/ethylacetate (1/1; v/v) as an eluent and affor-
D-Phenylalanine t-butyl ester
D
-2a: ½a 2D4
ꢀ
¼ ꢁ10:5 (c 1.01, CHCl3).
-2b
4.2.3.
L- and
D-Histidine t-butyl ester
L-2b and
D
ded 42.4 mg of D
-3a (54% yield). 1H NMR: (CDCl3) d 7.22–7.06 (m,
L
- or
D
-Histidine (0.50 g, 3.22 mmol) was charged in a round-
5H), 5.91 (br s, 1H, NH), 4.74 (q, J = 6.25 Hz, 13.60 Hz, 1H), 3.36 (q,
J = 5.88 Hz, 2H), 3.08 (dd, 2H, J = 5.88 Hz, 6.25 Hz), 2.36 (t, 2H,
bottomed flask equipped with a magnetic stirrer and suspended
in AcOtBu (25 mL). The suspension was treated with HClO4
(0.274 mL, 0.456 g, 4.54 mmol) while stirring to give a homoge-
neous solution. The reaction was stirred overnight at room temper-
ature and then extracted with water (3 ꢂ 30 ml) and HCl 0.5 M
(2 ꢂ 30 mL). The combined aqueous layers were added to solid
K2CO3 at pH 9 and then extracted with CH2Cl2 (3 ꢂ 80 mL). The
combined organic layers were dried over Na2SO4 and evaporated
to dryness to afford the product 2b as a yellow oil (0.330 g;
48.4% yield).
J = 5.88), 1.36 (s, 9H), 1.34 (s, 9H). ½a D24
¼ ꢁ25:9 (c 0.97, CHCl3).
ꢀ
ESI/MS: [M+H]+ = 393.1 [M+Na]+ = 415.1.
4.2.8. N-Boc-b-alanyl-
carnosine t-butyl ester)
N-Boc-2-azetidinone 1 (51.4 mg, 0.25 mmol,) and
-2b (105.6 mg, 0.5 mmol) were dissolved in 5 mL of solvent (DIPE
L
-histidine t-butyl ester (N-Boc-
L-
L
-3b
a-amino acid
L
or MTBE mixed with 5% of t-amyl alcohol). The solution obtained
was added to Lipase PS-D (60 mg/mL). The mixture was stirred at
37 °C, and samples were taken in order to measure the conversion
of the substrates. After the reaction was completed, the enzyme
was filtered off and the solvent was evaporated under vacuum.
The obtained residue was purified by chromatographic column
using as eluent a mixture of CH2Cl2/MeOH from 95/5 to 9/1 to af-
L
-Histidine t-butyl ester L-2b: 1H NMR (CDCl3): d: 7.53 s, 1Y,
6.84 (s, 1H), 4.96 (br s, 2H), 3.66 (dd, J = 4.04 Hz, 3.67 Hz, 1H),
3.05 (dd, J = 14.76 Hz, 3.85 Hz, 1H), 2.85 (dd, J = 14.73 Hz,
8.03 Hz, 1H), 1.44 (s, 9H); ½a D24
¼ þ4:05 (c 1.08, CHCl3); ESI/MS:
ꢀ
[M+H]+ = 221.9 [M+Na]+ = 243.9.
-2b: ½a 2D4
¼ ꢁ4:0 (c 1.03, CHCl3).
ꢀ
ford 65 mg of L
-3b (56% yield). 1H NMR (CDCl3): d 7.63 (s, 1H), 6.99
D
-histidine t-butyl ester
D
(br s, 1H), 6.83 (s, 1H), 5.54 (br s, 1H), 4.68 (dd, J = 12.01 Hz,
5.08 Hz, 1H), 3.41 (m, 2H), 3.09 (t, J = 5.2 Hz, 2H), 2.42 (t,
4.2.4.
L
-Trt-Histidine t-butyl ester
L-2c
J = 5.72 Hz), 1.43 (s, 9H), 1.42 (s, 9H). ½a D24
ꢀ
¼ þ5:5 (c 1.25, CHCl3).
Compound
L
-2c was prepared as described for 2b starting from
ESI/MS: [M+Na]+ = 405.1 [M+K]+ = 421.1.
Trt-His (1 g; 2.125 mmol). The obtained residue was purified by
chromatography using a mixture of CH2Cl2/CH3OH (9/1, v/v) as an
eluent. A pale yellow foam was isolated as product 2c (0.183 g) in
20% yield. 1H NMR (CDCl3): d 7.35 s, 1Y, 7.32 m, 9H), 7.12 (m,
6H), 6.62 (s, 1H), 3.67 (dd, J = 5.14 Hz, 4.0 Hz, 1H), 2.91 (dd,
J = 14.53 Hz, 4.04 Hz, 1H), 2.70 (dd, J = 14.31 Hz, 7.72 Hz, 1H), 1.91
4.2.9. N-Boc-b-Alanyl-
carnosine t-butyl ester)
N-Boc-2-Azetidinone 1 (51.4 mg, 0.25 mmol,) and
-2b (105.6 mg, 0.5 mmol) were dissolved in 5 mL of solvent (DIPE
D
-histidine t-butyl ester (N-Boc-
D-
D
-3b
a
-amino acid
(br s, 2H), 1.39 (s, 9H). ½a D24
ꢀ
¼ ꢁ4:0 (c 1.09, CHCl3). ESI/MS:
D
[M+H]+ = 454.0 [M+Na]+ = 476.1.
or MTBE mixed with 5% of t-amyl alcohol). The obtained solution
was added to Lipase PS-D (60 mg/mL). The mixture was stirred at
37 °C, and samples were taken in order to measure the conversion
of the substrates. After the reaction was completed, the enzyme
was filtered off and the solvent was evaporated under vacuum.
The obtained residue was purified by chromatographic column
using as eluent a mixture of CH2Cl2/MeOH from 95/5 to 9/1 to af-
4.2.5. Enzymatic synthesis of peptides using Lipase PS-D
N-Boc-2-azetidinone 1 (51.4 mg, 0.25 mmol,) and -amino acid
2a–c (0.5 mmol) were dissolved in 5 mL of solvent (DIPE or MTBE
mixed with 5% of t-amyl alcohol in case of reactions involving
and -histidine t-butyl ester -2b or -2b). The obtained solution
a
L
-
D
L
D
ford 65 mg of D
-3b (56,7% yield). 1H-NMR: (CDCl3) d 7.57 s, 1H),
was added to lipase PS-D (60 mg/mL). The mixture was stirred at
37 °C, with samples taken in order to measure the conversion of
substrates. After the reaction was completed, the enzyme was fil-
tered off and the solvent was evaporated under vacuum. The resi-
due obtained was purified by chromatographic column.
6.97 (br s, 1H), 6.80 (s, 1H), 5.56 (br s, 1H), 4.68 (q, J = 5.40 Hz,
12.6 Hz, 1H), 3.41 (m, 2H), 3.08 (t, J = 4.70 Hz, 2H), 2.40 (t,
J = 5.72 Hz, 2H), 1.43 (s, 9H), 1.41 (s, 9H). ½a D24
¼ ꢁ6:1 (c 1.05,
ꢀ
CHCl3). ESI/MS: [M+H]+ = 383.1 [M+Na]+ = 405.1.
4.2.6. N-Boc-b-alanyl-
N-Boc-2-azetidinone 1 (51.4 mg, 0.25 mmol,) and
-2a (110.6 mg, 0.5 mmol) were dissolved in 5 mL of solvent (DIPE).
L
-phenylalanine t-butyl ester
L
-3a
4.2.10. N-Boc-b-alanyl-
carnosine t-butyl ester)
N-Boc-2-azetidinone 1 (51.4 mg, 0.25 mmol,) and
-2c (110.6 mg, 0.5 mmol) were dissolved in 5 mL of solvent (DIPE).
L
-Trt-histidine t-butyl ester (N-Boc-
L-Trt-
a
-amino acid
L
-3c
L
a-amino acid
The obtained solution was added to Lipase PS-D (60 mg/mL). The
mixture was stirred at 37 °C, with samples taken in order to
measure the conversion of substrates. After the reaction was com-
pleted, the enzyme was filtered off and the solvent was evaporated
under vacuum. The obtained residue was purified by chromato-
graphic column using hexane/ethylacetate (1/1, v/v) as an eluent
L
The solution obtained was added to Lipase PS-D (60 mg/mL). The
mixture was stirred at 37 °C, and samples were taken in order to
measure the conversion of the substrates. After the reaction was
completed, the enzyme was filtered off and the solvent was evap-
orated under vacuum. The obtained residue was purified by chro-
matographic column using as eluent a mixture of CH2Cl2/MeOH
and afforded 44.5 mg of L
-3a (56.7% yield). 1H NMR (CDCl3): d
98/2 and afforded 81 mg of desired L
-3c (52% yield). 1H NMR
7.23–7.06 (m, 5H), 5.92 (br s, NH), 4.67 (dd, J = 5.88 Hz, 13.80 Hz,
1H), 3.29 (dd, J = 5.88 Hz, 6.25 Hz, 2H), 3.00 (dd, J = 6.25 Hz,
13.95 Hz, 2H), 2.29 (t, J = 6.25 Hz, 2H,), 1.36 (s, 9H), 1.34 (s, 9H).
(CDCl3): d 7.39 (s, 1H), 7.32 (m, 9H), 7.15 (m, 6H), 6.57 (s, 1H),
6.02 (br s, 1H), 4.68 (dd, J = 11.99 Hz, 4.41 Hz, 1H), 3.41 (dd,
J = 5.88 Hz, 5.51 Hz, 2H), 3.00 (dd, J = 13.98 Hz, 4.78 Hz, 2H), 2.40
½
a 2D4
415.1.
ꢀ
¼ þ26:4 (c 0.72, CHCl3). ESI/MS: [M+H]+ = 393.1 [M+Na]+ =
(dd, J = 5.51, 5.88 Hz, 2H), 1.34 (s, 9H), 1.26 (s, 9H). ½a D24
¼ þ9:6
ꢀ
(c 1.46, CHCl3) ESI/MS: [M+H]+ = 652.2, [M+Na]+ = 675.2.
4.2.7. N-Boc-b-alanyl-
D
-phenylalanine t-butyl ester
D
-3a
-amino acid
-2a (110.6 mg, 0.5 mmol) were dissolved in 5 mL of solvent
N-Boc-2-azetidinone 1 (51.4 mg, 0.25 mmol,) and
a
References
D
(DIPE). The obtained solution was added to Lipase PS-D (60 mg/
mL). The mixture was stirred at 37 °C, taking samples to measure
1. Seebach, D.; Beck, A. K.; Bierbaum, D. J. Chem. Biodivers. 2004, 1, 1111–1139.
2. Kimmerlin, T.; Seebach, D. J. Peptide Res. 2005, 65, 229–260.