R. Ramesh et al. / Tetrahedron 63 (2007) 10534–10542
10539
128.3, 128.2, 128.1, 128.0, 69.9, 67.7, 67.3, 67.1, 53.4; m/z
(HRMS) calcd for C26H25NO7+Na: 486.1529, found:
486.1527.
J2¼2.1 Hz, 1H), 1.33 (d, J¼6.6 Hz, 3H); dC (75 MHz,
CDCl3) 169.3, 156.5, 153.8, 135.9, 134.9, 134.8, 128.5,
128.4, 128.4, 128.3, 128.1, 127.9, 74.4, 69.7, 67.7, 67.6,
67.2, 57.5, 16.8; m/z (HRMS) calcd for C27H27NO7+Na:
478.1866, found: 478.1857.
4.2.4. Boc–Ser(Cbz)–OBn, 2d. White solid; column chro-
matography: EtOAc/hexane (1:9), Rf: 0.3; mp: 76 ꢀC; yield:
78%; FTIR (KBr): 3380 (br), 1751 (s), 1716 (s); dH
(300 MHz, CDCl3) 7.32–7.36 (m, 10H), 5.38 (br d,
J¼8.1 Hz, 1H), 5.17 (s, 2H), 5.12 (s, 2H), 4.54–4.63 (m,
2H), 4.40 (dd, J1¼10.7 Hz, J2¼3 Hz, 1H), 1.43 (s, 9H); dC
(75 MHz, CDCl3) 169.3, 155.1, 154.5, 134.9, 134.8, 128.6,
128.6, 128.5, 128.4, 128.4, 128.2, 80.3, 69.9, 67.6, 60.3,
52.9, 28.2; m/z (HRMS) calcd for C23H27NO7+Na:
452.1685, found: 452.1664.
4.2.10. Boc–Thr(Cbz)–OBn, 2j. White solid; column chro-
matography: EtOAc/hexane (2:8), Rf: 0.5; mp: 101 ꢀC;
yield: 60%; FTIR (KBr): 3383 (br), 1749 (s), 1719 (s); dH
(300 MHz, CDCl3) 7.32–7.35 (m, 10H), 5.30–5.35 (m,
1H), 5.25–5.28 (m, 1H), 5.02–5.13 (m, 4H), 4.48 (dd,
J1¼9.75 Hz, J2¼1.8 Hz, 1H), 1.44 (s, 9H) 1.34 (d,
J¼6 Hz, 3H); dC (75 MHz, CDCl3) 169.7, 155.8, 153.9,
135.0, 134.9, 128.6, 128.5, 128.4, 128.2, 80.2, 74.7, 69.8,
67.5, 57.0, 28.2, 16.8; m/z (HRMS) calcd for
C24H29NO7+Na: 466.1842, found: 466.1843.
4.2.5. Boc–Ser(Cbz)–OEt, 2e. Colorless oil; column chro-
matography: EtOAc/hexane (1:9), Rf: 0.3; yield: 85%;
FTIR (Neat): 3377 (br), 1751 (s), 1718 (s); dH (300 MHz,
CDCl3) 7.35–7.38 (m, 5H), 5.37 (br d, J¼7.5 Hz, 1H),
5.15 (s, 2H), 4.52–4.57 (m, 2H), 4.40 (dd, J1¼11.8 Hz,
J2¼4.5 Hz, 1H), 4.20 (q, J¼7.2 Hz, 2H), 1.44 (s, 9H), 1.25
(t, J¼7.2 Hz, 3H); dC (75 MHz, CDCl3) 169.3, 155.1,
154.6, 134.8, 128.6, 128.6, 128.3, 80.2, 69.9, 67.6, 61.9,
52.9, 28.2, 13.9; m/z (HRMS) calcd for C18H25NO7+Na:
390.1529, found: 390.1531.
4.2.11. Boc–Thr(Cbz)–OEt, 2k. Colorless oil; column
chromatography: EtOAc/hexane (2:8), Rf: 0.4; yield: 67%;
FTIR (Neat): 3375 (br), 1749 (s), 1718 (s); dH (300 MHz,
CDCl3) 7.35 (br s, 5H), 5.25–5.35 (m, 2H), 5.12 (s, 2H),
4.43 (dd, J1¼9.45 Hz, J2¼2.4 Hz, 1H), 4.11–4.20 (m, 2H),
1.45 (s, 9H), 1.36 (d, J¼6.6 Hz, 3H), 1.20 (t, J¼7.5 Hz,
3H); dC (75 MHz, CDCl3) 169.8, 155.9, 153.9, 134.9,
128.5, 128.3, 80.1, 74.8, 69.8, 61.8, 56.9, 28.2, 16.8, 13.9;
m/z (HRMS) calcd for C19H27NO7+H: 382.1866, found:
382.1861.
4.2.6. Boc–Ser(Cbz)-OiPr, 2f. Colorless oil; column chro-
matography: EtOAc/hexane (1:9), Rf: 0.3; yield: 79%;
FTIR (Neat): 3376 (br), 1750 (s), 1717 (s); dH (300 MHz,
CDCl3) 7.36–7.38 (m, 5H), 5.36 (br d, J¼7.5 Hz, 1H),
5.15 (s, 1H), 4.99–5.10 (m, 1H), 4.49–4.58 (m, 2H), 4.39
(dd, J1¼10.4 Hz, J2¼2.4 Hz, 1H), 1.44 (s, 9H), 1.25 (d,
J¼6 Hz, 3H), 1.20 (d, J¼6 Hz, 3H); dC (75 MHz, CDCl3)
168.8, 155.1, 154.6, 134.9, 128.6, 128.6, 128.3, 80.1, 69.9,
69.8, 67.7, 53.0, 28.2, 21.6, 21.5; m/z (HRMS) calcd for
C19H27NO7+Na: 404.1685, found: 404.1680.
4.2.12. Boc–Thr(Eoc)–OiPr, 5a. Colorless oil; column
chromatography: EtOAc/hexane (2:8), Rf: 0.5; yield: 62%;
FTIR (Neat): 3649 (br), 1748 (s), 1721 (s); dH (300 MHz,
CDCl3) 5.26–5.33 (m, 2H), 4.99–5.09 (m, 1H), 4.39 (dd,
J1¼9.6 Hz, J2¼2.1 Hz, 1H), 4.16 (q, J¼7.2 Hz, 2H), 1.46
(s, 9H), 1.35 (d, J¼6.6 Hz, 3H), 1.21–1.31 (m, 9H); dC
(75 MHz, CDCl3) 169.2, 155.8, 153.9, 79.9, 74.4, 69.5,
64.0, 57.1, 28.1, 21.6, 21.4, 16.8, 14.1; m/z (HRMS) calcd
for C15H27NO7+Na: 356.1685, found: 356.1661.
4.2.7. Cbz–Thr(Cbz)–OMe, 2g. Colorless oil; column
chromatography: EtOAc/hexane (2:8), Rf: 0.4; yield: 61%;
FTIR (Neat): 3359 (br), 1748 (s), 1728 (s); dH (300 MHz,
CDCl3) 7.33 (br s, 10H), 5.58 (br d, J¼9.31 Hz, 1H),
5.29–5.34 (m, 1H), 5.11 (s, 2H), 5.10 (s, 2H), 4.51 (br d,
J¼9.3 Hz, 1H), 3.66 (s, 3H), 1.33 (d, J¼6.3 Hz, 3H); dC
(75 MHz, CDCl3) 169.9, 156.4, 153.9, 135.9, 134.8, 128.5,
128.4, 128.1, 128.1, 127.9, 74.3, 69.7, 67.1, 57.3, 52.6,
16.8; m/z (HRMS) calcd for C21H23NO7+Na: 424.1372,
found: 424.1378.
4.2.13. Eoc–Ser(Eoc)–OMe, 5b. Colorless oil; column
chromatography: EtOAc/hexane (2:8), Rf: 0.5; yield: 92%;
FTIR (Neat): 3365 (br), 1751 (s), 1725 (s); dH (300 MHz,
CDCl3) 5.66 (br d, J¼8.1 Hz, 1H), 4.61–4.66 (m, 1H),
4.52 (dd, J1¼12 Hz, J2¼3.6 Hz, 1H), 4.42 (dd, J1¼12 Hz,
J2¼3.6 Hz, 1H), 4.11–4.23 (m, 4H), 3.79 (s, 3H), 1.24–
1.33 (m, 6H); dC (75 MHz, CDCl3) 169.6, 155.9, 154.5,
66.9, 64.3, 61.3, 53.1, 52.7, 14.3, 14.0; m/z (HRMS) calcd
for C26H25NO7+Na: 300.1059, found: 300.1052.
4.2.8. Boc–Thr(Cbz)–OMe, 2h. Colorless oil; column
chromatography: EtOAc/hexane (2:8), Rf: 0.4; yield: 64%;
FTIR (Neat): 3378 (br), 1750 (s), 1717 (s); dH (300 MHz,
CDCl3) 7.36 (s, 5H), 5.26–5.33 (m, 1H), 5.12 (s, 2H), 4.45
(dd, J1¼9.9 Hz, J2¼2.1 Hz, 1H), 3.69 (s, 3H), 1.44 (s,
9H), 1.35 (d, J¼6.6 Hz, 3H); dC (75 MHz, CDCl3) 170.3,
155.8, 153.9, 134.8, 128.5, 128.2, 126.9, 80.2, 74.6, 69.8,
56.9, 52.6, 28.1, 16.8; m/z (HRMS) calcd for
C18H25NO7+Na: 390.1529, found: 390.1514.
4.2.14. Eoc–Thr(Eoc)–OMe, 5c. Colorless oil; column
chromatography: EtOAc/hexane (2:8), Rf: 0.4; yield: 73%;
FTIR (Neat): 3361 (br), 1748 (s), 1727 (s); dH (300 MHz,
CDCl3) 5.45 (br d, J¼9.3 Hz, 1H), 5.25–5.32 (m, 1H),
4.50 (dd, J1¼9 Hz, J2¼2.1 Hz, 1H), 4.11–4.21 (m, 4H),
3.76 (s, 3H), 1.24–1.38 (m, 9H); dC (75 MHz, CDCl3)
170.3, 156.7, 153.9, 74.0, 64.2, 61.4, 57.2, 52.7, 16.9,
14.4, 14.1; m/z (HRMS) calcd for C11H19NO7+Na:
286.0903, found: 286.0902.
4.2.9. Cbz–Thr(Cbz)–OBn, 2i. Colorless oil; column chro-
matography: EtOAc/hexane (2:8), Rf: 0.5; yield: 52%; FTIR
(Neat): 3358 (br), 1748 (s), 1728 (s); dH (300 MHz, CDCl3)
7.31–7.33 (m, 15H), 5.56 (br d, J¼9.9 Hz, 1H), 5.31–5.35
(m, 1H), 4.99–5.15 (m, 6H), 4.55 (dd, J1¼9.45 Hz,
4.2.15. Compound 4. White solid; column chromatography:
EtOAc/hexane (1:9), Rf: 0.3; mp: 43 ꢀC; yield: 80%; FTIR
(KBr): 3335 (br), 1747 (s), 1722 (s); dH (300 MHz,
CDCl3) 7.28–7.34 (m, 10H), 5.00–5.12 (m, 5H), 4.16 (d,
J¼3.9 Hz, 2H), 3.81 (br s, 1H), 1.42–1.61 (m, 2H), 0.92 (t,