General Information
The pre-coated silica gel (0.25 mm thick layer over Al sheet, Merck, Darmstadt, Germany) TLC plates were used to monitor the reactions. Glass column packed silica gel (0.6–0.2 mm, 60 Å mesh size, Merck) were used for purification. The 1H-NMR and 13C-NMR were recorded in the designated solvents on a Bruker AVANCE DPX (300, 400, 500 or 600 MHz) spectrometer (Bruker, Billarica, MA, USA) using TMS as internal standard. The optical rotation was measured on an Atago (AP-300) polarimeter (Atago, Tokyo, Japan). The HR ESI was recorded on a Q-TOF Ultima API instrument (Micromass, Waters, Milford, MA, USA) at the Biomedical Mass Spectrometry Facility (BMSF), UNSW, Sydney (Australia). The single crystal X-Ray data were recorded on a Bruker Kappa APEX 11 CCD diffractometer. The IR and UV/Vis spectra were recorded on a Prestige 21 FTIR spectrometer (Shimadzu, Tokyo, Japan) and a Thermo Spectronic UV-1700 spectrophotometer (Thermo, Waltham, MA, USA), respectively.
Representative procedure for the synthesis of 4a–c, 5a–b and 6a–g: A mixture of (S)-2-bromopropanoic acid (5 mmol, 2 eq), SOCl2 (7.5 mmol, 2.5 eq) and catalytic amount of DMF (1 drop) was heated at 60 °C for 30 min. The resulting 2-haloacid chlorides 3a–d, without further purification, was slowly added dropwise to a stirred chilled solution of 5-cholo-3-methylanthranilic acid (1e) (2.5 mmol, 1 eq) and Et3N (2.5 mmol, 1 eq) in DMF (2 mL) at 0 °C. The reaction mixture was stirred overnight at room temperature. An excess of H2O was added and extracted with EtOAc (3 × 15 mL). The combined organic layer was dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure till a brownish liquid was obtained. This crude product was subjected to column chromatography on silica gel that afforded 5 (200 mg, 32%) and/or 4 (390 mg, 66%), both as white solids, by elution with 2% and 5% EtOAc in n-hexane.
(3R)-7,9-Dibromo-3-methyl-4,1-benzoxazepine-2,5-dione (
4a): R
f: 0.75 (EtOAc/
n-hexane 3:7),
= +12.0 (
c 0.5, MeOH); MP: 165 °C;
1H-NMR (300 MHz, CD
3OD): δ (ppm) 2.60 (3H, d,
J = 6.9 Hz, C
H3), 4.35 (1H, q,
J = 6.9 Hz, H
3), 7.70 (1H, d,
J = 1.5 Hz, H
8), 7.94 (1H, d,
J = 1.8 Hz, H
6); IR (KBr): ύ
max (cm
−1) 1697 (a broad signal of OC=O and NC=O); UV-Vis (MeOH): λ
max 304 nm (log ε = 3.21670 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 351, 349, 347 (6, 12, 6 in 1:2:1 ratio) [M]
+•, 279, 277 and 275 (39, 77 and 40 in 1:2:1 ratio) [M-C
3H
4O
2, A]
+•, 251, 249 and 247 (8, 17 and 9 in 1:2:1 ratio) [A-CO]
+•, ESI MS (
m/z) for C
10H
7Br
2NO
3: 373.8649, 371.8669 and 369.8690 found for 373.8645 [M+4+Na], 371.8665 [M+2+Na] and 369.8686 [M+Na] in 1:2:1.
(3R)-3,9-Dimethyl-4,1-benzoxazepine-2,5-dione (
4b): R
f: 0.65 (EtOAc/
n-hexane 3:7),
= +80.0 (
c 0.2, MeOH); MP: 190 °C;
1H-NMR (300 MHz, CDCl
3): δ (ppm) 1.83 (3H, d,
J = 6.9 Hz, C
H3), 2.27 (3H, s, Ar-C
H3), 4.55 (1H, q,
J = 6.9 Hz, H
3), 7.24 (1H, t,
J = 7.5 Hz, H
7), 7.49 (1H, d,
J = 7.5 Hz, H
8), 7.90 (1H, d,
J = 7.8 Hz, H
6), 9.56 (1H, s, NH);
13C-NMR (75 MHz, CDCl
3): δ (ppm) 18.8 (Ar-C
H3), 22.8 (C
1'), 55.9 (C
3), 126.2 (C
9), 126.3 (C
7), 129.3 (C
8), 129.4 (C
5a), 136.5 (C
6), 136.6 (C
9a), 168.0, 170.6 (C
2 and C
5); IR (KBr): ύ
max (cm
−1) 1697 (a broad signal of OC=O and NC=O); UV-Vis (MeOH): λ
max 294 nm (log ε = 3.32135 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 205 (72) [M]
+•, 133 (100) [M-C
3H
4O
2, A]
+•, 105 (100) [A-CO]
+•, ESI MS (
m/z) for C
11H
11NO
3: 228.0636 found for 228.0631 [M+Na].
(3R)-7-Chloro-3,9-dimethyl-4,1-benzoxazepine-2,5-dione (
4c): R
f: 0.61 (EtOAc/
n-hexane 3:7);
= +67.9 (
c 0.2, EtOAc); MP: 187 °C;
1H-NMR (300 MHz, CD
3OD): δ (ppm) 1.73 (3H, d,
J = 6.9 Hz, H
1'), 2.26 (3H, s, Ar-C
H3), 4.67 (1H, q,
J = 6.9 Hz, H
3), 7.50 (1H, broad s, H
8), 7.76 (1H, d,
J = 2.4 Hz, H
6);
13C-NMR (75 MHz, CD
3OD): δ (ppm) 18.2 (Ar-
CH
3), 22.1 (C
1'), 55.7 (C
3), 129.4 (C
8), 129.8 (C
5a), 135.0 (C
6), 135.6 (C
7), 168.0, 170.6 (C
2 and C
5); IR (KBr): ύ
max (cm
−1) 3362 (N-H), 1693 (a broad signal of OC=O and NC=O); UV-Vis (MeOH): λ
max 306 nm (log ε = 3.25701 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 241, 239 (13, 37 in 1:3 ratio) [M]
+•, 169, 167 (29, 100 in 1:3 ratio) [M-(3-methyloxirane-2-one), A]
+•, 141, 139 (31, 90 in 1:3 ratio) [A-CO]
+•; ESI MS (
m/z) for C
11H
10ClNO
3: 264.0217 and 262.0246 found for 264.0214 [M+2+Na] and 262.0242 [M+Na] in 1:3 ratio.
(1'R)-6-Chloro-2-(1'-chloroethyl)-8-methyl-3,1-benzoxazine-4-one (
5a): R
f: 0.87 (EtOAc/
n-hexane 3:7);
= −19.0 (
c 0.3, EtOAc); MP: 129 °C;
1H-NMR (300 MHz, CDCl
3): δ (ppm) 2.04 (3H, d,
J = 6.9 Hz, H
2'), 2.53 (3H, s, Ar-C
H3), 4.82 (1H, q,
J = 6.9 Hz, H
1'), 7.61 (1H, broad s, H
7), 8.00 (1H, broad s, H
5), IR (KBr): ύ
max (cm
−1) 1764 (lactonic OC=O), 1528 (C=N); UV-Vis (MeOH): λ
max 326 nm (log ε = 3.96534 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 261, 259 and 257 (2.5, 16 and 24 in 1:6:9 ratio) [M with 2 Cl]
+•, 224, 222 (22, 63 in 1:3 ratio) [M-
•Cl]
+, 196, 194 (31, 100 in 1:3 ratio) [M-H
3CC
∙(H)Cl]
+; ESI MS (
m/z) for C
11H
9Cl
2NO
2: 283.9849, 281.9878 and 279.9908 found for 283.9846 [M+4+Na], 281.9875 [M+2+Na] and 279.9905 [M+Na] in 1:6:9 ratio.
(1'S)-2-(1'-Bromoethyl)-6-chloro-8-methyl-3,1-benzoxazine-4-one (
5b): R
f: 0.87 (EtOAc/
n-hexane 3:7);
= −19.0 (
c 0.3, EtOAc); MP: 129 °C;
1H-NMR (300 MHz, CDCl
3): δ (ppm) 1.95 (3H, d,
J = 6.6 Hz, H
2'), 2.24 (3H, s, Ar-C
H3), 4.51 (1H, q,
J = 6.9 Hz, H
1'), 7.45 (1H, broad s, H
7), 7.86 (1H, broad s, H
5), IR (KBr): ύ
max (cm
−1) 1761 (lactonic OC=O), 1528 (C=N); UV-Vis (MeOH): λ
max 326 nm (log ε = 3.96534 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 305, 303 and 301 (1.9, 7.4 and 5.5 in 2:9:6 ratio) [M with Br and Cl]
+•, 224, 222 (22, 63 in 1:3) [M-
•Br]
+, 196, 194 (31, 100 in 1:3 ratio) [M-H
3CC
•(H)Br]
+; ESI MS (
m/z) for C
11H
9BrClNO
2: 327.9352, 325.9373 and 323.9402 found for 327.9350 [M+4+Na], 325.9370 [M+2+Na] and 323.9400 [M+Na] in 2:9:6 ratio.
(2'R)-4-Chloro-2-(2'-chloropropanamido)benzoic acid (
6a): The product (0.39 g, 67%) was precipitated out when reaction mixture was poured into ice chilled H
2O. R
f: 0.56 (EtOAc/
n-hexane 3:7);
= +80.0 (
c 0.5, EtOAc); MP: 187 °C;
1H-NMR (400 MHz, CDCl
3): δ (ppm) 1.82 (3H, d,
J = 7.2 Hz, H
3'), 4.54 (1H, q,
J = 7.2 Hz, H
2'), 7.15 (1H, dd,
J = 8.4, 1.6 Hz, H
5), 8.07 (1H, d,
J = 8.8 Hz, H
6), 8.82 (1H, d,
J = 1.5 Hz, H
3), 11.7 (1H, s, NH); IR (KBr): ύ
max (cm
−1) 1678 (OC=O), 1583 (NC=O); UV-Vis (MeOH): λ
max 306 nm (log ε = 3.950121 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 265, 263 and 261 (2, 11 and 21 in 1:6:9 ratio) [M]
+•, 200, 198 (15, 45 in 1:3 ratio) [M-H
3CC
•(H)Cl, A]
+, 182, 180 (45, 100) [A-H
2O]
+.
(2'S)-4-Chloro-2-(2'-chloro-3'-methylbutanamido)benzoic acid (
6b): R
f: 0.45 (EtOAc/
n-hexane 3:7),
= +16.9 (
c 0.6, MeOH); MP: 178 °C;
1H-NMR (300 MHz, CDCl
3): 1.00 (3H, d,
J = 6.3 Hz, C
H3), 1.09 (3H, d,
J = 6.6 Hz, H
4'), 2.55 (1H, m, H
3'), 4.35 (1H, d, 4.5 Hz, H
2'), 7.13 (1H, dd,
J = 8.7, 1.5 Hz, H
5), 8.06 (1H, d,
J = 8.6 Hz, H
6), 8.83 (1H, d,
J = 1.5 Hz, H
3), 11.78 (1H, s, NH); IR (KBr): ύ
max (cm
−1) 3500 (O-H), 3383 (N-H), 1666 (OC=O), 1595 (NC=O); UV-Vis (MeOH): λ
max 336 nm (log ε = 3.01872 L cm
−1 M
−1). ESI MS (
m/z) for C
12H
13Cl
2NO
3: 316.0111, 314.0140 and 312.0170 found for 316.0108 [M+4+Na], 314.0136 [M+2+Na] and 312.0167 [M+Na] in 1:6:9 ratio.
(2'S)-5-Bromo-2-(2'-chloro-3'-phenylpropanamido)benzoic acid (
6c): R
f: 0.14 (EtOAc/
n-hexane 3:7),
= +17.0 (
c 1.0, MeOH); MP: 110 °C;
1H-NMR (500 MHz, CD
3OD): 3.21 (1H, dd,
J = −14.0, 8.0 Hz, H
α3'), 3.43 (1H, dd,
J = −14.0, 8.0 Hz, H
β3'), 4.69 (1H, dd,
J = 8.0, 6.0 Hz, H
2'), 7.17-7.24 (5H, m, Ph), 7.63 (1H, dd,
J = 9.0, 2.5 Hz, H
4), 8.11 (1H, d,
J = 2.5 Hz, H
6), 8.48 (1H, d,
J = 9.0, H
3);
13C-NMR (125 MHz, CD
3OD) δ (ppm): 42.46 (C
3'), 62.29 (C
2'), 116.76 (C
1''), 119.97 (C
1), 123.08 (C
4''), 128.18 (C
3), 129.45, 130.54 (C
3'' and C
2''), 134.92 (C
4), 137.47 (C
5), 137.71 (C
6), 140.58 (C
2), 169.23 (NC=O), 169.57 (OC=O); IR (KBr): ύ
max (cm
−1) 3028 (O-H), 2916 (N-H), 1709 (OC=O), 1531 (NC=O); UV-Vis (MeOH): λ
max 317 nm (log ε = 3.56741 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 385, 383, 381 (1, 5, 3 in 2:9:6 ratio) [M]
+•, 226, 224 (16, 15 in 1:1 ratio) [M-
•CH
2(Cl)Bn and H
2O, A]
+, 217, 215 (53, 52 in 1:1) [M-
•CH
2(Cl)Bn and CO]
+, 198, 196 (56, 56) [A-CO]
+.
(2'S)-5-Bromo-2-(2'-chloro-3'-methylbutanamido)benzoic acid (
6d): R
f: 0.45 (EtOAc/
n-hexane 3:7),
= +32.0 (
c 1.0, MeOH); MP: 178 °C;
1H-NMR (300 MHz, CDCl
3): 1.00 (3H, d,
J = 6.3 Hz, C
H3), 1.09 (3H, d,
J = 6.6 Hz, H
4'), 2.55 (1H, m, H
3'), 4.35 (1H, d, 4.5 Hz, H
2'), 7.13 (1H, dd,
J = 8.7, 1.5 Hz, H
4), 8.06 (1H, d,
J = 8.6 Hz, H
3), 8.83 (1H, d,
J = 1.5 Hz, H
6), 11.78 (1H, s, NH); IR (KBr): ύ
max (cm
−1) 3500 (O-H), 3383 (N-H), 1666 (OC=O), 1595 (NC=O); UV-Vis (MeOH): λ
max 336 nm (log ε = 3.01872 L cm
−1 M
−1); ESI MS (
m/z) for C
12H
13BrClNO
3: 359.9615, 357.9644 and 355.9665 found for 359.9612 [M+4+Na], 357.9642 [M+2+Na] and 355.9663 [M+Na] in 2:9:6 ratio.
(2'S)-4-Chloro-2-(2'-chloro-3'-methylpentanamido)benzoic acid (
6e): R
f: 0.15 (EtOAc/
n-hexane 3:7),
= +16.2 (
c 1.0, MeOH); MP: 126 °C;
1H-NMR (600 MHz, CD
3OD): 0.96 (3H, d,
J = 6.6 Hz, C
H3), 0.98 (3H, d,
J = 6.6 Hz, H
5'), 1.85–1.98 (3H, m, H
3' and H
4'), 4.51 (1H, dd,
J = 9.6, 4.8 Hz, H
2'), 7.18 (1H, dd,
J = 8.4, 1.8 Hz, H
5), 8.06 (1H, d,
J = 8.4 Hz, H
6), 8.69 (1H, d,
J = 1.8, H
3);
13C-NMR (125 MHz, CD
3OD) δ (ppm): 21.56 (Me), 23.06 (C
5'), 26.52 (C
4'), 45.44 (C
3'), 60.48 (C
2'), 116.42 (C
1), 120.97 (C
5), 124.53 (C
3), 133.99 (C
6), 141.13 and 142.81 (C
2 and C
4), 170.39 (NC=O), 170.44 (OC=O); IR (KBr): ύ
max (cm
−1) 3221 (O-H), 3120 (N-H), 1640 (OC=O), 1550 (NC=O); UV-Vis (EtOAc): λ
max 307 nm (log ε = 3.44321 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 307, 305 and 303 (0.1, 1.2 and 2.1 in 1:6:9 ratio) [M]
+•, 251, 249 and 247 (6, 45 and 77 in 1:6:9 ratio) [M-C
4H
8, A]
+•, 200, 198 (3, 7 in 1:3) [A-
•CH
2Cl, B]
+, 182, 180 (37, 80) [B-H
2O, C]
+, 173, 171 (29, 100) [B-CO]
+, 155, 153 (17, 52) [C-CO]
+.
(2'S)-4-Chloro-2-(2'-chloro-3'-phenylpropanamido)benzoic acid (
6f): R
f: 0.17 (EtOAc/
n-hexane 1:1),
= +35.2 (
c 1.0, MeOH); MP: 121 °C;
1H-NMR (500 MHz, CD
3OD): 3.23 (1H, dd,
J = −14.0, 7.5 Hz, H
α3'), 3.44 (1H, dd,
J = −14.0, 6.0 Hz, H
β3'), 4.71 (1H, dd,
J = 7.5, 6.0 Hz, H
2'), 7.15 (1H, dd,
J = 8.5, 2.0 Hz, H
5), 7.19-7.26 (5H, m, Ph), 8.01 (1H, d,
J = 8.5 Hz, H
6), 8.66 (1H, d,
J = 2.0, H
3);
13C-NMR (125 MHz, CD
3OD) δ (ppm): 42.43 (C
3'), 62.24 (C
2'), 116.35 (C
1''), 120.91 (C
5), 124.55 (C
3), 128.12 (C
4''), 129.47, 130.57 (C
3'' and C
2''), 133.91 (C
6), 137.45 (C
1), 141.04 (C
4), 142.56 (C
2), 169.46 (NC=O), 170.18 (OC=O); IR (KBr): ύ
max (cm
−1) 3221 (O-H), 3001 (N-H), 1670 (OC=O), 1543 (NC=O); UV-Vis (MeOH): λ
max 306 nm (log ε = 3.09876 L cm
−1 M
−1). LR EIMS:
m/z in amu (% abundance) 304, 302 (9, 31 in 1:3 ratio) [M-
•Cl]
+, 182, 180 (25, 8) [M-
•CH
2(Cl)Bn and H
2O, A]
+.
(2'S)-5-Bromo-2-(2'-chloro-3'-methylpentanamido)benzoic acid (
6g): R
f: 0.12 (EtOAc/
n-hexane 3:7),
= +23.3 (
c 0.2, MeOH); MP: 118 °C;
1H-NMR (500 MHz, CD
3OD): 0.96 (3H, d,
J = 6.5 Hz, C
H3), 0.98 (3H, d,
J = 6.0 Hz, H
5'), 1.84–1.97 (3H, m, H
3'and H
4'), 4.51 (1H, dd,
J = 9.0, 5.0 Hz, H
2'), 7.69 (1H, dd,
J = 9.0, 2.5 Hz, H
4), 8.17 (1H, d,
J = 2.5 Hz, H
3), 8.53 (1H, d,
J = 9.0, H
6);
13C-NMR (125 MHz, CD
3OD) δ (ppm): 21.59, 23.06 (C
H3 and C
5'), 25.53 (C
4'), 45.49 (C
3'), 60.53 (C
2'), 116.75 (C
1), 119.97 (C
5), 123.20 (C
4), 135.02 (C
3), 137.87 (C
6), 140.89 (C
2), 169.76 (NC=O), 170.26 (OC=O); IR (KBr): ύ
max (cm
−1) 3259 (O-H), 3044 (N-H), 1685 (OC=O), 1531 (NC=O); UV-Vis (MeOH): λ
max 310 nm (log ε = 3.23921 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 351, 349 and 347 (4, 12 and 11) [M]
+•, 226, 224 (62, 43) [M-∙CH
2(Cl)Bn and H
2O, A]
+, 217, 215 (99, 100) [M-∙CH
2(Cl)Bn and CO]
+, 199, 197 (61, 60) [A-CO]
+.
(3R)-8-Chloro-3-methyl-4,1-benzoxazepine-2,5-dione (
4d): A mixture of
6a (1 mmol, 1 eq) and anhydrous K
2CO
3 (1.5 mmol, 1.5 eq) in DMF (1 mL) was heated at 80 °C for 3 h. Excess of chilled H
2O was added, the mixture was neutralized with dilute HCl (5 mL) and extracted with EtOAc (2 × 15 mL). The combined organic layer was dried over anhydrous Na
2SO
4, filtered and concentrated under reduced pressure to afford the crude product. It was purified by column chromatography using 5% EtOAc in
n-hexane as mobile phase to afford pure
4d. R
f: 0.57 (EtOAc/
n-hexane 3:7);
= +54.0 (
c 0.2, MeOH); MP: 134 °C;
1H-NMR (400 MHz, CDCl
3): δ (ppm) 1.61 (3H, d,
J = 6.8 Hz, H
1'), 4.79 (1H, q,
J = 4.8 Hz, H
3), 7.00 (1H, d,
J = 1.6 Hz, H
9), 7.26 (1H, dd,
J = 8.4, 1.6 Hz, H
7), 7.92 (1H, d,
J = 8.4 Hz, H
6), 7.94 (1H, s NH); IR (KBr): ύ
max (cm
−1) 3262 (N-H), 1707 (a broad signal of OC=O and NC=O); UV-Vis (MeOH): λ
max 302 nm (log ε = 3.98631 L cm
−1 M
−1); LR EIMS:
m/z in amu (% abundance) 227 and 225 (10 and 30 in 1:3) [M]
+•, 155 and 153 (30 and 100 in 1:3 ratio) [M-(3-methyloxirane-2-one)]
+•, 183 and 181 (3 and 10 in 1:3 ratio) [M-CO]
+•.