(8-Oxo-5,6,7,8-tetrahydro-3-indolizinyl)methyl acetate 26
References
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Polygonatine A 7 (9 mg, 0.054 mmol), Ac2O (11.0 lL, 0.116 mmol)
and pyridine (0.5 cm3) were stirred at 80 ◦C for 2 h. The mixture
was cooled to rt, made acidic with conc. HCl, diluted with
water and extracted with CH2Cl2 (3 × 20 cm3). The combined
organic extracts were washed further with water to remove the
pyridinium salt. The organic layer was dried (MgSO4), filtered
and evaporated under reduced pressure to give (8-oxo-5,6,7,8-
tetrahydro-3-indolizinyl)methyl acetate 26 (12 mg, ca. 100%) as a
brown oil; Rf 0.67 (CH2Cl2–MeOH, 19 : 1); mmax (thin film)/cm−1
=
=
2923 (w), 1729 (s, C O), 1661 (s, C O), 1539 (m), 1434 (m), 1337
(m), 1236 (m), 1036 (m) and 789 (m); dH (200 MHz; CDCl3; Me4Si)
6.99 (1H, d, J 4.1, pyrrole-H), 6.33 (1H, d, J 4.1, pyrrole-H), 5.10
(2H, s, CH2OAc), 4.09 (2H, t, J 5.9, NCH2), 2.61 (2H, apparent
=
t, J ca. 6.5, CH2C O), 2.32 (2H, apparent quintet, J ca. 6.1,
=
CH2CH2C O) and 2.09 (3H, s, COCH3), dC (75 MHz; CDCl3)
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=
=
187.4 (C O), 170.5 (OC O), 132.0 and 131.6 (C-3, C-8a), 113.4
and 112.6 (C-1, C-2), 57.1 (CH2OAc), 42.5 (C-5), 35.9 (C-7), 23.2
(C-6) and 20.8 (COCH3); m/z 208 (M+ + 1, 7%), 207 (M+, 52),
166 (7), 165 (9), 149 (10), 148 (100), 147 (8), 120 (9), 106 (5) and
78 (5) (Found: M+, 207.0898. C11H13NO3 requires 207.0895).
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(a) Polygonatine A 7 (66 mg, 0.40 mmol) was stirred in EtOH
(5 cm3) with a catalytic amount of conc. HCl (1 drop) for 16 h
at rt. The solvent was evaporated under reduced pressure and the
residue was dissolved in CH2Cl2 (10 cm3) and washed with water
(2 × 10 cm3). The organic layer was dried (MgSO4), filtered and
evaporated under reduced pressure to give chromatographically
homogeneous polygonatine B 5 (33 mg, 43%); see below for
characterisation.
(b) (8-Oxo-5,6,7,8-tetrahydro-3-indolizinyl)methyl acetate 26
(13.3 mg, 0.064 mmol) was heated under reflux in EtOH (5 cm3)
for 2 days. The mixture was cooled to rt and the solvent was
evaporated under reduced pressure to give polygonatine B 5
(11.3 mg, 91%) as a yellow oil; Rf 0.30 (CH2Cl2–MeOH, 19 :
1); mmax (thin film)/cm−1 2975 (w), 2928 (w), 2870 (w), 1658 (s,
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=
C O), 1538 (m), 1480 (m), 1435 (m), 1338 (m), 1120 (m), 1089
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(m) and 787 (w); dH (300 MHz; CDCl3; Me4Si) 6.97 (1H, d, J 4.0,
1-H), 6.22 (1H, d, J 4.0, 2-H), 4.48 (2H, s, CH2OEt), 4.11 (2H, t,
J 5.9, NCH2), 3.51 (2H, q, J 7.0, OCH2CH3), 2.59 (2H, t, J 6.4,
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=
=
CH2C O), 2.30 (2H, apparent quintet, J ca. 6.1, CH2CH2C O)
and 1.22 (3H, t, J 7.0, OCH2CH3); dC (75 MHz; CDCl3) 187.5
25 See, for example: (a) W. S. Emerson and E. P. Agnew, J. Am. Chem.
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=
(C O), 134.3 and 131.8 (C-3, C-8a), 113.1 and 111.6 (C-1, C-2),
65.5 (OCH2CH3), 63.9 (CH2OEt), 42.5 (C-5), 36.0 (C-7), 23.3 (C-
6) and 15.1 (OCH2CH3); m/z 193 (M+, 37%), 164 (3), 149 (12), 148
(100), 136 (3), 120 (10), 106 (4) and 78 (4) (Found: M+, 193.1104.
C11H15NO2 requires 193.1103).
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Acknowledgements
29 For recently reported examples of simple pyrrole alkaloids containing
these motifs, see the following: (a) Y.-W. Chin, S. W. Lim, S.-H. Kim,
D.-Y. Shin, Y.-G. Suh, Y.-B. Kim, Y. C. Kim and J. Kim, Bioorg. Med.
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50, 6318–6321.
This work was supported by grants from the National Research
Foundation, Pretoria (grant number 2053652) and the University
of the Witwatersrand. We are grateful to Mrs S. Heiss (University
of the Witwatersrand) and Dr P. R. Boshoff (formerly of the
Cape Technikon) for recording NMR spectra and mass spectra,
respectively.
This journal is
The Royal Society of Chemistry 2006
Org. Biomol. Chem., 2006, 4, 1032–1037 | 1037
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