8210
S. B. Wan, T. H. Chan / Tetrahedron 60 (2004) 8207–8211
(C)-afzelechin gallate (130 mg, 82% yield): mp 257–
259 8C (decompose); [a]DZ45.5 (cZ0.5, Me2CO); 1H
NMR (acetone-d6/D2O, 3:1, v/v, 400 MHz): d 7.39 (A of
AB, JZ7.3 Hz, 2H), 7.12 (s, 2H), 6.92 (B of AB, JZ7.3 Hz,
2H), 6.17 (s, 1H), 6.06 (s, 1H), 5.45 (bs, 1H), 5.20 (d, JZ
6.8 Hz, 1H), 3.08 (A of ABt, JZ16.4, 4.9 Hz, 1H), 2.84 (B
of ABt, JZ16.4, 6.8 Hz, 1H); 13C NMR (acetone-d6/D2O,
3:1, v/v, 400 MHz): d 160.0, 151.2, 151.0, 150.6, 150.5,
149.5, 139.3, 132.7, 123.4, 122.3, 114.3, 109.4, 103.3, 92.6,
89.9, 88.7, 18.5; HRMS (ESI) calcd for C22H19O9 (MCH)
427.1029, found 427.1024.
3.1.9. (K)-epiAfzelechin ((K)-2). The compound was
prepared following the synthetic method of (C)-afzelechin
with (K)-13 as the starting marterial. The yield was 82%;
mp 196–198 8C; [a]DZK59 (cZ3, Me2CO); lit. [a]DZ
K58.9 (cZ3, EtOH);15 1H NMR (CDCl3, 400 MHz) d 7.41
(A of AB, JZ8.6 Hz, 2H), 6.91 (B of AB, JZ8.6 Hz, 2H),
6.12 (d, JZ2.3 Hz, 1H), 6.02 (d, JZ2.3 Hz, 1H), 5.00 (bs,
1H), 4.32 (bs, 1H), 2.95 (A of ABt, JZ16.6, 4.5 Hz, 1H),
2.77 (B of ABt, JZ16.6, 3.6 Hz, 1H); 13C NMR (CDCl3,
400 MHz) d 150.4, 150.2, 150.0, 124.2, 122.8, 122.3, 108.8,
106.3, 93.2, 93.1, 89.5, 88.8, 72.4, 59.8, 21.7; HRMS (ESI)
calcd for C15H15O5 (MCH) 275.0919, found 275.0932.
3.1.7. (C)-(2R)-5,7-Bis(benzyloxy)-2-(4-benzyloxy-
phenyl)-chroman-3-one ((C)-12). Dess-Martin periodi-
nane (6.3 mL, 15% g/mL in CH2Cl2, 2.2 mmol) was added
in one batch to a stirred solution of (C)-9 (600 mg,
1.1 mmol) in CH2Cl2 (30 mL) under an N2 atmosphere. The
mixture was stirred at rt for about 2 h till TLC showed the
absence of starting material. Subsequently, saturated
NaHCO3 solution (15 mL) and 10% Na2S2O3 aqueous
solution (15 mL) were added to quench the reaction. The
organic layer was separated, and the aqueous layer was
extracted with CH2Cl2. The combined organic phases were
dried (MgSO4) and evaporated. The residue was purified by
flash chromatography on silica gel (benzene) and then
recrystallized in CHCl3 and ether to afford the desired
compound (448 mg, 75%): mp 141–143 8C, [a]DZC46
3.1.10. (K)-(2R,3R)-cis-5,7-Bis(benzyloxy)-2-(4-benzyloxy-
phenyl)-chroman-3-yl 3,4,5-tris(benzyloxy)benzoate
((K)-14)). Following the preparation procedure for (C)-
10, compound (K)-14 was synthesized with (K)-13 as
starting material. The yield was 82%; mp 134–135 8C;
[a]DZK51.3 (cZ1.0, CH3Cl); 1H NMR (CDCl3,
400 MHz) d 7.39–7.25 (m, 32H), 6.85 (d, JZ8.7 Hz, 2H),
6.37 (d, JZ2.2 Hz, 1H), 6.30 (d, JZ2.2 Hz, 1H), 5.5 (bs,
1H), 5.10 (d, JZ4.9 Hz, 1H), 5.08 (s, 2H), 5.03 (s, 2H), 5.02
(s, 2H), 5.01 (s, 2H), 4.99 (s, 2H), 4.97 (s, 2H), 3.08 (bs,
2H); 13C NMR (CDCl3, 400 MHz) d 165.1, 158.7, 158.4,
157.9, 155.6, 152.1, 142.1, 137.8, 136.8, 136.7, 136.5,
128.5, 128.4, 128.1, 128.0, 127.9, 127.8, 127.7, 127.4,
127.3, 127.1, 124.9, 114.5, 108.9, 100.8, 94.5, 93.7, 77.3,
75.0, 70.8, 70.0, 69.8, 68.7, 25.9; HRMS (ESI) calcd for
C64H55O9 (MCH) 967.3846, found 967.3862.
1
(cZ1.1, CHCl3); H NMR (CDCl3, 400 MHz) d 7.41–7.30
(m, 15H), 7.27 (A of AB, JZ8.7 Hz, 2H), 6.95 (B of AB,
JZ8.7 Hz, 2H), 6.37 (d, JZ2.1 Hz, 1H), 6.34 (d, JZ
2.1 Hz, 1H), 5.26 (s, 1H), 5.03 (s, 2H), 5.01 (s, 2H), 4.99 (s,
2H), 3.68 (AB, JZ21.5 Hz, 2H); 13C NMR (CDCl3,
400 MHz) d 205.3, 159.3, 158.9, 156.9, 154.6, 136.7,
136.5, 136.4, 128.6, 128.5, 128.1, 128.0, 127.9, 127.5,
127.3, 127.1, 114.9, 102.0, 95.7, 95.0, 83.1, 70.1, 70.0, 69.9,
33.8; HRMS (ESI) calcd for C36H31O5 (MCH) 543.2171,
found 543.2190.
3.1.11. (K)-epiAfzelechin gallate ((K)-15). The com-
pound was prepared following the synthetic method of
(C)-afzelechin gallate with (K)-14 as the starting material.
The yield was 80%; mp 242–244 8C (decompose); [a]DZ
K177 (cZ0.9, Me2CO); lit. K181.9 (cZ0.9, Me2CO);15
1H NMR (acetone-d6/D2O, 3:1, v/v, 400 MHz): d 7.49 (A of
AB, JZ8.6 Hz, 2H), 7.13 (s, 2H), 6.92 (B of AB, JZ8.6 Hz,
2H), 6.16 (d, JZ2.2 Hz, 1H), 6.12 (d, JZ2.2 Hz, 1H), 5.56
(bs, 1H), 5.25 (bs, 1H), 3.16 (A of ABt, JZ17.4, 4.5 Hz,
1H), 3.02 (B of AB, JZ17.4 Hz, 1H); 13C NMR (acetone-
d6/D2O, 3:1, v/v, 400 MHz): d 160.3, 151.0, 150.7, 150.2,
139.3, 132.6, 123.6, 122.3, 114.5, 109.1, 103.4, 92.2, 89.9,
89.0, 71.4, 63.3, 19.9; HRMS (ESI) calcd for C22H19O9
(MCH) 427.1029, found 427.1045.
3.1.8. (K)-(2R,3R)-cis-5,7-Bis(benzyloxy)-2-(4-benzyloxy-
phenyl)-chroman-3-ol ((K)-13). Under an N2 atmosphere,
the ketone ((C)-12) (280 mg, 0.51 mmol) was dissolved in
dry THF (10 mL), and the solution was cooled to K78 8C.
Then L-selectride (1 mL, 1 M solution in THF, 1 mmol)
was added dropwise. The resulting solution was stirred at
K78 8C overnight. When TLC showed the reaction was
completed, saturated NaHCO3 aqueous solution (10 mL)
was added to quench the reaction. The organic layer was
separated and the aqueous layer was extracted with EtOAc.
The combined organic phases were dried (MgSO4) and
evaporated. The residue was purified by flash chromato-
graph on silca gel (5% EtOAC/benzene) and then
recrystallized with ethanol and EtOAC to afford the desired
product (200 mg, 71%) as a white solid: mp 110–111 8C,
[a]DZK5.7 (cZ1.0, CHCl3); 1H NMR (CDCl3, 400 MHz)
d 7.35–7.22 (m, 17H), 6.93 (d, JZ8.7 Hz, 2H), 6.18 (s, 2H),
4.98 (s, 2H), 4.92 (s, 2H), 4.90 (s, 2H), 4.87 (d, JZ4.4 Hz,
1H), 4.16 (bs, 1H), 2.95 (A of ABt, JZ17.4, 1.8 Hz, 1H),
2.87 (B of ABt, JZ17.4, 4.4 Hz, 1H); 13C NMR (CDCl3,
400 MHz) d 158.7, 158.5, 158.2, 155.3, 136.9, 136.8, 130.5,
128.5, 128.4, 127.9, 127.8, 127.6, 127.5, 127.4, 127.1,
114.8, 100.9, 94.6, 93.9, 78.3, 70.0, 69.9, 69.8, 66.2, 28.3;
HRMS (ESI) calcd for C36H33O5 (MCH) 545.2328, found
545.2320.
Acknowledgements
This work was supported by the Areas of Excellence
Scheme established under the University Grants Committee
of the Hong Kong Special Administrative Region, China
(Project No. AoE/P-10/01). We thank the Hong Kong
Polytechnic University for financial support. T. H. C.
acknowledges the support of McGill University for the
granting of a leave.
References and notes
1. Shode, F. O.; Mahomed, A. S.; Rogers, C. B. Phytochemistry
2002, 61, 955–5.