Paper
RSC Advances
ꢀ
with a 9% aqueous solution of NaHCO
1
3
, twice with aqueous HCl CDCl
3
, 25 C): d ¼ 170.86, 169.58, 66.21, 60.32, 51.01, 31.27,
N, and once with brine, and then nally dried (Na SO ). The 26.73, 21.06, 19.00, 18.82 ppm. GC/MS (CI): m/z (%) 228 (51) [(M
2 4
solvent was evaporated under reduced pressure to afford the + C H ) ], 216 (32) [(M + C H ) ], 188 (100) [(M + H) ], 157 (76),
+
+
+
3
5
2
5
corresponding N-acetyl derivatives 3j–p as colourless oils in 146 (83), 128 (68), 102 (2).
1
quantitative yield. Spectroscopic data for 3j–n were comparable
N-Acetyl N-methyl isoleucine methyl ester (3p). H NMR (300
2
a
ꢀ
to those reported in the literature.
MHz, CDCl
3
, 25 C), (two rotamers): d ¼ 4.99 (d, J ¼ 10.5 Hz, 1H,
1
N-Acetyl alanine methyl ester (3j). H NMR (300 MHz, CDCl
3
,
a-CH), 3.71 and 3.67 (2s, 3H, OCH
), 2.14 and 2.10 (2s, 3H, CH CO), 2.00–1.90 (m, 1H, b-CH),
) ppm. 1.40–1.26 (m, 1H, CH ), 1.10–1.00 (m, 1H, CH ), 0.97 and 0.96
3
), 2.95 and 2.83 (2s, 3H, N–
ꢀ
2
5 C): d ¼ 6.28 (s, 1H, NH), 4.58 (m, 1H, a-CH), 3.70 (s, 3H, CH
3
3
OCH
3
), 2.02 (s, 3H, CH
3
CO), 1.40 (d, J ¼ 7.2 Hz, 3H, CH
3
2
2
1
3
ꢀ
C NMR (75 MHz, CDCl , 25 C): d ¼ 173.7, 169.5, 52.4, 48.0, (2d, J ¼ 6.9 Hz, 3H, CH ) ppm.
3
3
+
1
2
5
1
3.1, 18.6 ppm. GC/MS (EI): m/z (%) 145 (13) [(M) ], 102 (86) (70),
N-Acetyl glycine t-butyl ester (3q). H NMR (300 MHz, CDCl ,
ꢀ
3
+
9 (5), 44 (100). HRMS (ESI) for ([C H NO ] + Na) : calcd 25 C): d ¼ 3.92 (d, J ¼ 5.1 Hz, 2H, a-CH), 2.04 (s, 3H, CH ), 1.47
6
11
3
3
+
13
ꢀ
68.0637, found 168.0630 [M + Na] .
(s, 9H, C(CH
3
)
3
), ppm. C NMR (75 MHz, CDCl
3
, 25 C): d ¼
1
N-Acetyl valine methyl ester (3k). H NMR (300 MHz, CDCl
3
,
170.3, 169.3, 82.3, 42.1, 28.0, 22.9 ppm. HRMS (ESI) for
ꢀ
+
+
2
5
2
¼
5 C): d ¼ 6.22 (d, 1H, NH, J ¼ 6.6 Hz), 4.55 (dd, J ¼ 8.7, J ¼ [(C
8 3
H15NO ) + H] : calcd 174.1130, found 174.1122 [M + H] ,
+
.1 Hz, 1H, a-CH), 3.74 (s, 3H, OCH
.01 (s, 3H, CH
3 3 2
), 2.13 (m, 1H, CH(CH ) ), 196.0945 [M + Na] .
1
3
CO), 0.93 (d, J ¼ 6.9 Hz, 3H, CH(CH
3
)
2
), 0.90 (d, J
N-Acetyl phenylalanine benzyl ester (3r). H NMR (300 MHz,
1
3
ꢀ
ꢀ
6.9 Hz, 3H, CH(CH ) ) ppm. C NMR (75 MHz, CDCl , 25 C): CDCl , 25 C): d ¼ 7.35–7.21 (m, 8H, ArH), 7.00–6.97 (m, 2H,
3
2
3
3
d ¼ 172.7, 170.2, 57.1, 52.1, 31.2, 23.1, 18.8, 17.8 ppm. GC/MS ArH), 6.02 (d, J ¼ 6.9 Hz, 1H, NH), 5.14–5.13 (m, 2H, COOCH ),
2
+
+
(
1
CI): m/z (%) 214 (13) [(M + C H ) ], 202 (16) [(M + C H ) ], 4.93 (m, 1H, a-CH), 3.12–3.09 (m, 2H, CH Ph), 1.96 (s, 3H,
3 5 2 5 2
+
13
ꢀ
74 (60) [(M + H) ], 156 (9), 142 (65), 132 (50), 114 (100), 101 (7). CH
3
CO) ppm. C NMR (75 MHz, CDCl
3
, 25 C): d ¼ 171.7, 169.9,
+
HRMS (ESI) for ([C
8
H
15NO
3
] + H) : calcd 174.1130, found 135.8, 135.2, 129.4, 128.8, 128.7, 128.6, 127.2, 67.4, 53.3, 37.9,
+
+
174.1134 [M + H] .
3
23.2 ppm. HRMS (ESI) for [(C18H19NO ) + H] : calcd 298.1443,
1
+
+
N-Acetyl leucine methyl ester (3l). H NMR (300 MHz, CDCl
3
,
found 298.1437 [M + H] , 320.1254 [M + Na] .
ꢀ
1
2
5 C): d ¼ 6.50 (d, J ¼ 7.68 Hz, 1H, NH), 4.52 (m, 1H, a-CH), 3.69
N-Acetyl tyrosine(O-t-butyl)t-butyl ester (3s). H NMR (300
ꢀ
(
s, 3H, OCH ), 1.99 (s, 3H, CH CO), 1.62–1.40 (m, 3H, CH CH), MHz, CDCl , 25 C): d ¼ 7.31 (d, J ¼ 8.4 Hz, 2H, ArH), d ¼ 7.90 (d,
3
3
2
3
1
3
1
.40–1.26 (m, 1H, CH ), 0.85–0.87 (m, 6H, CH(CH ) ) ppm.
C
J ¼ 8.4 Hz, 2H, ArH), 6.04 (br s, s, 1H, NH), 4.74 (dd, J ¼ 6.6 Hz, J
2
3 2
ꢀ
NMR (75 MHz, CDCl , 25 C): d ¼ 173.8, 170.1, 52.1, 50.6, 41.3, ¼ 5.7 Hz, 1H, a-CH), 3.09–3.02 (m, 2H, b-CH), 2.02 (s, 3H,
3
1
3
24.7, 22.8, 22.7, 21.8 ppm. GC/MS (CI): m/z (%) 228 (20) [(M + CH
3
CO), 1.38 (s, 9H, C(CH
3
ꢀ
)
3
), 1.40 (s, 9H, C(CH
3
)
3
), ppm.
, 25 C): d ¼ 170.9, 169.3, 146.4, 131.1,
] + 129.9, 124.0, 90.8, 82.4, 53.6, 37.5, 28.8, 27.9, 23.2 ppm. HRMS
C
+
+
+
C
3 5 2 5 3
H ) ], 216 (35) [(M + C H ) ], 188 (100) [(M + H) ], 170 (5), 156 NMR (75 MHz, CDCl
(
60), 146 (55), 128 (88), 86 (9). HRMS (ESI) for ([C
9
H
17NO
3
+
+
+
Na) : calcd 210.1106, found 210.1103 [M + Na] .
4
(ESI) for [(C19H29NO ) + H] : calcd 336.2175, found 336.2133 [M
1
+
+
N-Acetyl isoleucine methyl ester (3m). H NMR (300 MHz, + H] , 358.1987 [M + Na] .
ꢀ
1
CDCl , 25 C): d ¼ 6.06 (s, 1H, NH), 4.54 (d, J ¼ 8.7 Hz, J ¼ 4.8 Hz,
N-Acetyl glutamic acid(O-t-butyl)methyl ester (3t). H NMR
3
ꢀ
1
H, a-CH), 3.67 (s, 3H, OCH ), 1.96 (s, 3H, CH CO), 1.78 (m, 1H, (300 MHz, CDCl , 25 C): d ¼ 6.34 (d, J ¼ 7.5 Hz, 1H, NH), 4.74
3
3
3
b-CH), 1.35 (ddd, J ¼ 7.5 Hz, J ¼ 4.8 Hz, J ¼ 4.8 Hz, 1H, CH ), (dt, J ¼ 8.0 Hz, J ¼ 5.1 Hz, 1H, a-CH), 3.67 (s, 3H, OCH ), 2.35–
2
3
3
1
1
.12 (m, 1H, CH
2
), 0.85 (s, 3H, CH
3
), 0.82 (s, 3H, CH
3
) ppm.
C
2.15 (m, 2H, b-CH
2
), 2.05 (ddd, J ¼ 14.1 Hz, J ¼ 7.3 Hz, J ¼
ꢀ
NMR (75 MHz, CDCl
2
C
3
, 25 C): d ¼ 172.7, 169.8, 56.4, 51.9, 37.9, 2.2 Hz, 1H, g-CH), 1.95 (s, 3H, CH
3
CO), 1.87 (ddd, J ¼ 14.1 Hz, J
1
3
5.2, 23.2, 15.3, 11.5 ppm. GC/MS (CI): m/z (%) 228 (51) [(M + ¼ 6.1 Hz, J ¼ 1.3 Hz, 1H, g-CH), 1.37 (s, 9H, C(CH
3
)
3
) ppm.
, 25 C): d ¼ 172.6, 172.2, 170.0, 80.8, 52.4,
] + H) : calcd 51.8, 31.4, 28.0, 27.2, 23.0 ppm. HRMS (ESI) for [(C12 ) +
C
+
+
+
ꢀ
3 5 2 5 3
H ) ], 216 (32) [(M + C H ) ], 188 (100) [(M + H) ], 157 (76), 146 NMR (75 MHz, CDCl
+
(
1
83), 128 (68), 102 (2). HRMS (ESI) for ([C
88.1287, found 188.1279 [M + H] , 210.1099 [M + Na] .
9
H
17NO
3
H21NO
5
+
+
+
+
Na] : calcd 282.1317, found 282.1307 [M + Na] .
1
1
N-Acetyl phenylalanine methyl ester (3n). H NMR (300 MHz,
N-Acetyl lysine(N-Boc)methyl ester (3u). H NMR (300 MHz,
ꢀ
ꢀ
1
ꢀ
CDCl , 25 C): d ¼ 7.32–7.24 (m, 3H, ArH), 7.09 (dd, J ¼ 7.9 Hz, J CDCl , 25 C): H NMR (300 MHz, CDCl , 25 C): d ¼ 6.48 (d, J ¼
3
3
3
¼
1.8 Hz, 2H, ArH), 6.02 (d, J ¼ 6.6 Hz, 1H, NH), 4.88 (dt, J ¼ 7.5 Hz, 1H, NH), 4.73 (m, 1H, NH), 4.50 (dd, J ¼ 12.6 Hz, J ¼
.8 Hz, J ¼ 5.8 Hz, 1H, a-CH), 3.72 (s, 3H, OCH ), 3.14 (dd, J ¼ 7.5 Hz, 1H, a-CH), 3.67 (s, 3H, OCH ), 3.04–2.99 (m, 2H, 3-CH ),
CO), 1.75 (m, 1H, b-CH), 1.58 (m, 1H, b-CH),
7
1
5
3
3
2
3.83 Hz, J ¼ 5.7 Hz, 1H, b-CH), 3.07 (dd, J ¼ 13.83 Hz, J ¼ 1.96 (s, 3H, CH
3
1
3
13
.7 Hz, 1H, b-CH), 1.99 (s, 3H, CH
3
CO) ppm. C NMR (75 MHz, 1.44–1.27 (m, 4H, g-CH
, 25 C): d ¼ 172.0, 169.5, 135.8, 129.2, 128.5, 127.1, 53.1, NMR (75 MHz, CDCl
2
+ d-CH
2
), 1.36 (s, 9H, C(CH
3
)
3
) ppm.
C
ꢀ
ꢀ
CDCl
3
3
, 25 C): d ¼ 172.1, 169.1, 155.2, 78.1, 51.3,
+
5
2
2.2, 37.8, 23.0 ppm. HRMS (ESI) for ([C H NO ] + Na) : calcd 51.1, 38.9, 30.8, 28.6, 27.4, 21.9, 21.4 ppm. HRMS (ESI) for
12 15 3
44.0950, found 244.0941 [M + Na] .
+
+
+
[(C H N O ) + H] : calcd 303.1920, found 303.1904 [M + H] ,
14 26 2 5
1
+
N-Acetyl N-methyl valine methyl ester (3o) (two rotamers). H 325.1737 [M + Na] .
ꢀ
NMR (300 MHz, CDCl
3
, 25 C), (two rotamers): d ¼ 4.88 (d, 1H, J
¼
10.5 Hz, a-CH), 3.69 and 3.65 (2s, 3H, OCH
2s, 3H, N–CH ), 2.16 and 2.12 (2s, 3H, CH CO), 2.27–2.19 (m,
H, b-CH), 0.95 and 0.94 (d, J ¼ 6.6 Hz, 3H, CH(CH ), 0.86 and At the end of the rst experiment and aer the recovery of the
) ppm. C NMR (75 MHz, free aniline, the IL was treated with 5% aqueous HCl (2 mL) and
3
), 2.94 and 2.82
4
Recycling of [Bmim][BF ] in the synthesis of 2a
(
3
3
1
0
3 2
)
1
3
.82 (d, J ¼ 6.9 Hz, 3H, CH(CH
3 2
)
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 36482–36491 | 36489