Structure-activity study of epi-gallocatechin gallate (EGCG) analogs as proteasome inhibitors

Article abstract of DOI:10.1016/j.bmc.2004.12.056

The structure-activity relationship of a number of synthetic green tea polyphenol analogs involving modifications of A ring and B ring of epi-gallocatechin gallate (EGCG) as proteasome inhibitors has been examined. It was found that in B ring, a decrease in the number of OH groups led to decreased potency. Introduction of a hydrophobic benzyl group into the 8 position of A ring did not significantly affect the proteasome-inhibitory potency.

Full text of DOI:10.1016/j.bmc.2004.12.056

Bioorganic & Medicinal Chemistry 13 (2005) 2177–2185
Structure–activity study of epi-gallocatechin gallate
(EGCG) analogs as proteasome inhibitors
Sheng Biao Wan,a Kristin R. Landis-Piwowar,b, Deborah J. Kuhn,b Di Chen,b
Q. Ping Doub and Tak Hang Chana,*
aDepartment of Applied Biology and Chemical Technology and the Open Laboratory of Chirotechnology,
Institute of Molecular Technology for Drug Discovery and Synthesis, The Hong Kong Polytechnic University,
Hung Hom, Hong Kong, SAR, China
bThe Prevention Program, Barbara Ann Karmanos Cancer Institute, and Department of Pathology, School of Medicine,
Wayne State University, Detroit, MI, USA
Received 14 December 2004; revised 28 December 2004; accepted 28 December 2004
Abstract—The structure–activity relationship of a number of synthetic green tea polyphenol analogs involving modifications of A
ring and B ring of epi-gallocatechin gallate (EGCG) as proteasome inhibitors has been examined. It was found that in B ring, a
decrease in the number of OH groups led to decreased potency. Introduction of a hydrophobic benzyl group into the 8 position
of A ring did not significantly affect the proteasome-inhibitory potency.
Ó 2005 Elsevier Ltd. All rights reserved.
R1
1. Introduction
R1
R2
R3
R2
R3
HO
O
Regular drinking of green tea has been associated with
reduced risk of several forms of cancer.1,2 The biological
effects of green tea are often attributed to the polyphe-
nols, in particular, the catechins.3 A number of catechins
have been identified in green tea infusions.4,5 They are
(ꢀ)-epi-afzelechin (EZ, 1), (+)-catechin (C, 2), (ꢀ)-epi-
catechin (EC, 3), (ꢀ)-gallocatechin (GC, 4), (ꢀ)-epi-gal-
locatechin (EGC, 5), their respective 3-gallate esters (ꢀ)-
EZG (6), (+)-CG (7), (ꢀ)-ECG (8), (ꢀ)-GCG (9) and
(ꢀ)-EGCG (10). Although a number of cancer-related
proteins are affected by tea polyphenols, the exact mech-
anism of tea-mediated cancer prevention is not known.2
Recently, we proposed that inhibition of proteasome
may be a key mechanism in the cancer prevention activ-
ity of green tea2,6 (Fig. 1).
HO
O
OR
OR
OH
OH
1: R=R1=R3=H, R2=OH
3: R=R1=H, R2=R3=OH
5: R=H, R1=R2=R3=OH
2: R=R1=H, R2=R3=OH
4: R=H, R1=R2=R3=OH
7: R=gallate, R1=H, R2=R3=OH
9: R=gallate, R1=R2=R3=OH
6: R=gallate, R1=R3=H, R2=OH
8: R=gallate, R1=H, R2=R3=OH
10:R=gallate, R1=R2=R3=OH
Figure 1. Various catechins in green tea.
regulation of cell death. The eukaryotic proteasome con-
tains three known activities: chymotrypsin-like mediated
by the b5-subunit, trypsin-like by the b2-subunit and the
caspase-like by the b1-subunit.7 Proteasome inhibitors
have been considered as potential anticancer drugs.8 In-
deed, MLN-341 (formerly PS-341), a dipeptidyl boronic
compound and a potent and selective inhibitor of the
chymotrypsin-like activity of the 20S proteasome, has
recently been approved for the treatment of hematologi-
cal malignant neoplasms.9 In the case of natural green
tea polyphenols, it was reported that the naturally
occurring ester bond-containing green tea polyphenols,
The proteasome is responsible for the degradation of
most cellular proteins via the ubiquitin/proteasome-
dependent degradation pathway and plays an important
role in the up-regulation of cell proliferation and down-
*
Corresponding author. Tel.: +86 852 2766 5605; fax: +86 852 2364
9932; e-mail addresses: doup@karmanos.org; bcchanth@polyu.
edu.hk
Tel.: +1 313 966 0641; fax: +1 313 966 7368.
0968-0896/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.12.056

2178
S1 hydrophobic pocket
S. B. Wan et al. / Bioorg. Med. Chem. 13 (2005) 2177–2185
ence of a hydrophobic substituent in the A ring in affect-
2.51
H
Thr21
ing the biological activity? To answer this point, we have
prepared the two benzyl compounds 15 and 16 and
examined their biological activities.
O
O
Lys32
OH
O
O
3.35
B
OH
H
O
O
HO
O
HO
O
HO
O
H
OH
2.16
A
C
OGallate
OGallate
H
OGallate
OH
OH
14
Ala49
OH
O
3.37
H
Ala146
11
12
2.59
13=ent12
O
O
H
O
OH
H
CH2PH
O
2.74
OH
CH2PH
O
Thr1
N-termial threonine
HO
HO
O
OH
OGallate
OH
OGallate
O
G
H
Gly47
N
2.28
OH
OH
15
16
O
N
OH
H
2.82
Ser131
2. Results and discussion
Figure 2. Docking model of (ꢀ)-EGCG in the b5-subunit of 20S
2.1. Enantioselective syntheses of epi-40-deoxycatechin
gallate (12 and 13) and epi-30,40-dideoxycatechin gallate
(14)
˚
proteasome. The number is distance in A for the H-bond indicated.
such as EGCG, GCG and ECG, possess the ability to
inhibit proteasome activity in vitro and in vivo.6 In con-
trast, the polyphenols without the gallate ester function,
such as EGC, GC and EC, are not inhibitors of protea-
some.6 Through our synthetic efforts, we have recently
prepared the natural (ꢀ)-EGCG,10 (ꢀ)-GCG,11 (ꢀ)-
ECG12 and (+)-CG12 as well as their respective enantio-
mers.10–12 Unexpectedly, it was found that the unnatural
enantiomers were equally or more potent as the natural
compounds in inhibiting the chymotrypsin-like activity
of proteasome.11 A mechanistic model, with in silico
docking calculations, to account for their inhibition of
proteasome has been proposed.11 In this model, the poly-
phenol gallate ester, for example, (ꢀ)-EGCG, binds to
the active site of the b5-subunit of 20S proteasome.
The A ring of (ꢀ)-EGCG acts as the phenyl ring of a
phenylalanine mimic, binding to the hydrophobic S1
pocket of the b5-subunit (Fig. 2). The ester bond of
(ꢀ)-EGCG is then in reasonable proximity (about
In all our previously reported syntheses of EGCG and
other catechins, a Friedel–Crafts reaction was used to
build up the connection between A ring (17) and B ring
(18) (Scheme 1).10–13 The same Friedel–Crafts coupling
reaction was used in the syntheses of epi-afzelechin
gallate (6) and afzelechin gallate (11).15 It was noted
however that the yields of coupling reactions declined
as the number of alkoxy groups in the B ring diminished
(Table 1). When the same coupling reaction was carried
out with 30-benzyloxycinnamyl alcohol (18d) or cinn-
amyl alcohol (18e), the product yields were so low that
rendered the reaction impractical for the synthesis of
12–14. The low yields in the latter two cases were prob-
ably due to the absence of para alkoxy group, which was
needed to stabilize the carbenium ion intermediate nec-
essary for the Friedel–Crafts reaction. Alternative meth-
od for the construction of the fragment 19 was sought.
We attempted the Mitsunobu reaction using the stan-
dard conditions of triphenylphosphine and di-isopropyl
azodicarboxylate (DIAD) in toluene in the hope of get-
ting the ether 20, which may then undergo the Claisen
rearrangement to the desired 19. Much to our delight,
compound 19 was obtained directly under the Mits-
unobu conditions in reasonable yield. The reaction was
not subject to electronic effect, and the yields for 19d
and 19e were the same as those for 19a–c (Table 1).
The intermediate 20 was confirmed by carrying out the
Mitsunobu reaction of 18d0 (Scheme 2). A mixture of
products was obtained, which included 19d, 20 and 21.
˚
3.18 A) from the N-terminal Thr (Thr 1) OH function,
which is responsible for the protease catalytic activity.
Inhibition is then due to the irreversible transfer of the
gallate moiety from (ꢀ)-EGCG to the hydroxy oxygen
of Thr 1. This model has successfully accounted for
the similar activities of the natural and unnatural enan-
tiomers by recognizing the pseudo-symmetry of the B
and G (gallate) rings in the active site.13 It is also consis-
tent with subsequent structure–activity studies, which
showed that both the A and C rings were necessary
for the proteasome inhibition activity but the oxygen
in C ring can be replaced with the CH2 isostere.14
R1
R1
In this study, we intend to probe the structure–activity
relationship on the following two issues. Firstly, how
critical is the various OH substituents in the B ring? In
order to answer this question, the four gallate analogs
11–14, which are not present in natural green tea cate-
chins, have been prepared and their biological activities
compared with compounds 6–10. Secondly, since the A
ring is embedded in the hydrophobic region of the b5-
subunit of 20S proteasome, what is the effect of the pres-
R2
R3
R2
R3
BnO
OH
BnO
OH
a
+
OBn
or b
OBn
OH
19
17
18
Scheme 1. Friedel–Crafts versus Mitsunobu condensation: (a) H2SO4/
SiO2/CH2Cl2, rt; (b) Ph3P/DIAD/toluene, ꢀ20 °C.

S. B. Wan et al. / Bioorg. Med. Chem. 13 (2005) 2177–2185
2179
Table 1. Yields of Friedel–Crafts versus Mitsunobu reactions between
17 and 18 to give 19 (Scheme 1)
the bromo compound 24d, which then cyclized in ace-
tone with K2CO3 as base to produce (+)-25d with cis
S,S configuration. Evidently, two SN2 substitution reac-
tions must have occurred at the benzylic carbon giving
an overall retention of configuration at that centre.
The same cyclization method was used to synthesize
(+)-25e. Esterification of 25d or 25e with 3,4,5-tris(ben-
zyloxy)benzoyl chloride, followed by hydrogenolysis
gave the desired compounds 12 and 14 in overall yield
of 14% and 15%, respectively. When compound 19d
was converted to the dihydroxy compound (ꢀ)-22d with
AD-mix-b, and the same reaction sequence was fol-
lowed, 13 was obtained. It had the same NMR spectra
as the (+)-enantiomer 12 but with opposite optical
rotation.
R1
R2
R3
Friedel–Craftsa
yield (%)
Mitsunobub
yield (%)
19a
19b
19c
19d
19e
OBn
OBn
H
OBn
OBn
OBn
H
OBn
H
60
47
37
10
8
48
50
53
60
62
H
OBn
H
H
H
H
a H2SO4/SiO2/CH2Cl2, rt.
b Ph3P/DIAD/toluene, ꢀ20 °C.
Compound 20 could be isolated by flash chromatogra-
phy at 0 °C but rearranged readily at room temperature
on silica gel to 19d.
2.2. Enantioselective syntheses of 8-benzyl-epi-catechin
gallate (15) and 8-benzylcatechin gallate (16)
With compounds 19d and 19e at hand, the syntheses of
12, 13 and 14 followed more or less the path previously
used (Scheme 3).10 Steroselective Sharpless dihydroxyl-
ation, using AD-mix-a as the oxidant, was performed
on the TBS protected 19d and 19e, and then deprotec-
tion to give compounds (+)-22d and (+)-22e, respec-
tively, with S,S configuration. Reaction of (+)-22d
with triethyl formate and PPTS gave the acetal 23d.
Conversion of 23d to the benzopyran skeleton could
not be achieved with PPTS at 60 °C, the conditions pre-
viously used for the synthesis of EGCG.10 This is again
because of the absence of para alkoxy group in the B
ring to facilitate the nucleophilic opening of the acetal
function at the benzylic position. Alternatively, com-
pound 23d reacted with acetyl bromide at 0 °C to give
In order to synthesize compounds 15 and 16, the precur-
sor compound 27 was required. Providently, compound
27 was a by-product in the preparation of the starting
materials 17 (Scheme 4) used in the previous syntheses
of green tea catechins.10–13,15 In the literature synthesis
of 17,10,16 ethanethiol was used to debenzylate 1,3,5-
tribenzyloxybenzene (26). The reaction yielded at vari-
ous times low yield of 17 (11%) with a substantial
amount of 27 (56%). We eventually traced the low yield
of 17 to the volatility of ethanethiol, which easily es-
caped the reaction mixture under reflux conditions.
Changing the debenzylation agent with the higher boil-
ing n-butanethiol, the reaction gave consistently 17 as
the major product (64% yield) with 27 (16%) as the min-
or component.
BnO
O
Friedel–Crafts coupling of 27 with 18b gave a fair yield
(46%) of the coupled product 28. The conversion of 28
to compounds 15 and 16 was accomplished by following
the sequence of reactions outlined in Scheme 5 without
difficulties.
OBn
HO
Ph3P/DIAD
THF/0 oC
OBn
OBn
+
19d
17
+
20
BnO
O
18d'
OBn
2.3. Proteasome inhibition
OBn
We then tested whether these synthetic compounds can
inhibit the proteasomal chymotrypsin-like activity of
purified 20S prokaryotic proteasome, using (ꢀ)-EGCG
21
Scheme 2. Isolation of intermediate 20.
R2
R2
R3
d
BnO
OH
a,b,c
BnO
OH
19d or
R3
O
O
OH
OH
19e
OEt
OBn
OBn
23
22d R2=H, R3=OBn;
22e R2=R3=H
e
R2
R3
R2
BnO
OH
BnO
O
f,g
h,i
R3
Br
OCHO
12 or 13,
14
OH
OBn
OBn
24
25
Scheme 3. Reagents and conditions: (a) TBSCl/imidazole/DMF, rt; (b) AD-mix-a/MeSO2NH2/H2O/t-BuOH/CH2Cl2/0 °C; (c) TBAF/THF, rt; (d)
CH(OEt)3/PPTS/CH2Cl2, rt; (e) AcBr/CH2Cl2/0 °C; (f) K2CO3/acetone, rt; (g) K2CO3/MeOH; (h) 3,4,5-tri(benzyloxy)benzoyl chloride/DMAP/
CH2Cl2, rt; (i) H2/Pd(OH)2/MeOH/THF, rt.

2180
S. B. Wan et al. / Bioorg. Med. Chem. 13 (2005) 2177–2185
Table 2. Effects of natural and synthetic tea polyphenols on 20S
prokaryotic proteasome activities
CH2Ph
OH
BnO
OBn
BnO
BnO
OH
a or b
Compound
IC50 (lM)
Reference
+
(ꢀ)-EGCG, 10
(ꢀ)-ECG, 8
(+)-CG, 7
(ꢀ)-EZG, 6
(+)-ZG, 11
12
0.30
0.58
0.73
2.69
4.56
0.84
1.22
4.56
0.73
0.39
0.75
0.59
This work
Ref. 12
Ref. 12
OBn
OBn
OBn
27
26
17
This work
This work
This work
This work
This work
Ref. 12
Scheme 4. Preparation of compound 27: (a) EtSH/NaH/DMF, 150 °C;
(b) BuSH/NaH/DMF, 150 °C.
13
14
(+)-ECG
15
as a positive control.6,11,12 The results are summarized in
Table 2. By comparing the IC50s of the series: (ꢀ)-
EGCG (0.30), (ꢀ)-ECG (0.58), (ꢀ)-EZG (2.69), 12
(0.84) and 14 (4.56), all with the same absolute configu-
rations at the two stereogenic centres, one can conclude
that as the number of OH group in the B ring dimin-
ishes, the inhibition activity declines. Furthermore, com-
paring (ꢀ)-EZG with compound 12, the meta OH is
more effective than the para OH group in enhancing
inhibition activity. This result is consistent with the
model in Figure 2 where there is H-bonding between
the meta OH with the amino acids in the active site.
The nearly equal potencies of compound 12 and its
enantiomer 13 agree with all our previous observation
that the natural polyphenols and their synthetic enantio-
mers have nearly equal activities in the inhibition of
proteasome.11,12 Because 14 without OH group in B ring
still inhibits the proteasomal chymotrypsin-like activity
mediated by b5-subunit though with reduced potency
(Table 2), it suggests to us that interaction of Thr21
and Ala49 of b5 to the two OH groups in B ring of
EGCG (Fig. 2) might not be essential for the protea-
some-inhibitory activity, but may be required for
improving the potency of EGCG. Compound 14, as well
as other analogs, will be docked to the b5-subunit to vali-
date this prediction. As for hydrophobic substitution in
the A ring, compounds 15 and 16 were found to be
slightly more active than the counterparts (+)-ECG
and (ꢀ)-CG or the natural (+)-CG. This suggests that
the hydrophobic benzyl substitution at the C-8 position
of A ring did not significantly affect the proteasome-
inhibitory potency. This may be due to the rather large
steric size of the benzyl group. Substitution with alkyl
groups of different sizes will be required to explore the
dimension of this hydrophobic pocket.
This work
Ref. 12
This work
(ꢀ)-CG
16
posed with the polyphenol binding to the active site of
b5-subunit of 20S proteasome. Remained unexplored
is the variation in the structure in the gallate (G) ring.
This will be the subject of another study.18
4. Experimental
4.1. General
The starting materials and reagents, purchased from
commercial suppliers, were used without further purifi-
cation. Literature procedures were used for the prepara-
tion of 3,5-bis(benzyloxy)phenol (17),10,16 3,4,5-tris(benz-
yloxy)benzoic acid,10 silica gel supported H2SO4,10 (E)-
3,4-bis(benzyloxy)cinnamyl alcohol (18b)12 and (E)-3-
(benzyloxy)cinnamyl alcohol (18d).4 Anhydrous THF
was distilled under nitrogen from sodium benzophenone
ketyl. Anhydrous methylene chloride was distilled under
nitrogen from CaH2. Anhydrous DMF was distilled
OBn
OBn
CH2Ph
OBn
OBn
CH2Ph
OH
BnO
OH
a
BnO
+
OBn
OH
OBn
28
18b
27
b,c,d
OBn
OBn
OBn
CH2Ph
OH
OBn
e
CH2Ph
O
BnO
Several of these compounds have also been tested in cul-
tured tumour cells. We found that they moderately
inhibited cellular proteasome activity and induced apop-
tosis in a portion of tumour cells.17 These data suggest
that although these compounds act as proteasome inhib-
itors in vivo, their potency is decreased probable due to
their decreased stability.17
f,g
BnO
OH
OH
16
OH
OBn
29
OBn
30
h
OBn
OBn
OBn
f,g
OBn
CH2Ph
O
CH2Ph
O
BnO
BnO
i
15
OH
O
OBn
OBn
31
32
3. Conclusions
Scheme 5. Reagents and conditions: (a) H2SO4/SiO2/CH2Cl2, rt; (b)
TBSCl/imidazole/DMF, rt; (c) AD-mix-b/MeSO2NH2/H2O/t-BuOH/
CH2Cl2/0 °C; (d) TBAF/THF, rt; (e) CH(OEt)3/PPTS/CH2Cl2, 60 °C;
(f) 3,4,5-tris(benzyloxy)benzoyl chloride/DMAP/CH2Cl2, rt; (g) H2/
Pd(OH)2/MeOH/THF, rt; (h) Dess–Martin periodinane/CH2Cl2, rt; (i)
L-Selectride/THF, ꢀ78 °C to rt.
We have studied thus far the structure–activity relation-
ship in the inhibition of proteasome by green tea poly-
phenols by modifications of A, C and B rings as well
as the stereochemistry of the two stereogenic centres.
The results appear to be consistent with the model pro-

S. B. Wan et al. / Bioorg. Med. Chem. 13 (2005) 2177–2185
2181
under vacuum from CaH2. Reaction flasks were flame-
dried under a stream of N2. All moisture-sensitive reac-
tions were conducted under a nitrogen atmosphere.
Flash chromatography was carried out using silica-gel
60 (70–230 mesh). The melting points were uncorrected.
1H NMR and 13C NMR spectra were measured with
TMS as an internal standard when CDCl3 or acetone-
d6 were used as solvent. High-resolution (ESI) MS spec-
128.2, 127.8, 127.7, 127.6, 127.3, 127.2, 127.1, 126.5,
125.7, 119.7, 114.9, 112.4, 109.6, 107.3, 91.4, 71.1,
70.5, 70.3, 28.8, 26.6; HRMS (ESI): calcd for
C50H44O5Na (M+Na) 747.3086, found 747.3096.
4.4. (ꢀ)-(1R,2R)-3-[2,4-Bis(benzyloxy)-5-benzyl-6-
hydroxy-phenyl]-1-[3,4-bis(benzyloxy)phenyl]propane-
1,2-diol ((ꢀ)-29)
tra were recorded using
spectrometer.
a QTOF-2 Micromass
The propene 28 (3.4 g, 4.6 mmol) was dissolved in dry
DMF (30 mL), and to this solution imidazole (1.03 g,
15.2 mmol) and TBSCl (1.2 g, 7.8 mmol) were added
successively. The resulting mixture was stirred at rt for
3 days, and then saturated Na2CO3 solution was added
to quench the reaction. The mixture was extracted with
EtOAc. The organic layers were combined, dried
(MgSO4) and evaporated. The residue was purified by
flash chromatograph on silica gel (n-hexane and
EtOAc = 9/1 v/v) to afford [3,5-bis(benzyloxy)-6-benz-
yl-2-[3-[3,4-bis(benzyloxy)phenyl]allyl]phenoxy]-tert-
butyldimethylsilane. This material was used in the next
step without further purification.
4.2. 2-Benzyl-3,5-bis(benzyloxy)phenol (27)
Butanethiol (19 g, 216 mmol) was added dropwise to a
stirred suspension of sodium hydride (60% dispersion
in mineral oil, 2.4 g, 100 mmol) in dry DMF (120 mL)
at 0 °C. After 1 h, 1,3,5-tribenzyloxybezene (24 g,
60 mmol) was added in 10 batches and the mixture
was heated to 150 °C for 1.5 h. After the reaction was
cooled, water (500 mL) was added and the mixture
was extracted with EtOAc. The combined organic layers
were dried (MgSO4) and evaporated. The residue was
purified by flash chromatography on silica gel (benzene)
to give the product 17 as white solid (9.3 g, 64%) after
recrystallization from carbon tetrachloride and product
27 as white solid (3.0 g, 16%) after recrystallization from
EtOAc and hexane.
AD-mix-b (13.0 g) and methanesulfonamide (0.87 g)
were dissolved in a solvent mixture of t-BuOH
(50 mL) and H2O (50 mL). The resulting mixture was
stirred at rt for 5 min, then the mixture was cooled to
0 °C and a solution of [3,5-bis(benzyloxy)-6-benzyl-2-
[3-[3,4-bis(benzyloxy)phenyl]allyl]phenoxy]-tert-butyldi-
methylsilane in dichloromethane (50 mL) was added.
After the mixture had been stirred overnight, two more
batches of AD-mix-b (13.0 g each) and methanesulfon-
amide (0.87 g each) were added in each 24 h intervals.
After another 24 h of stirring at 0 °C, TLC showed that
the reaction was completed. Then a 10% Na2S2O3 solu-
tion was added to quench the reaction. The mixture was
extracted with EtOAc. The organic phases were com-
bined, dried (MgSO4) and evaporated. The residue was
purified by flash chromatograph on silica gel (n-hexane
and EtOAc = 4/1 v/v) to afford [3,5-bis(benzyloxy)-6-
benzyl-2-[3-[3,4-bis(benzyloxy)phenyl]-1,2-dihydroxyl-
propyl]phenoxy]-tert-butyldimethylsilane. The resulting
compound was dissolved in THF (75 mL), and TBAF
(10 mL, 1 M in THF) was added. The resulting mixture
was stirred at rt for 4 h, and saturated NaHCO3 solution
was added. The mixture was extracted with EtOAc, and
the organic layers were combined, dried (MgSO4) and
evaporated. The residue was purified by flash chroma-
tography on silica gel (EtOAc/hexane = 1/2 v/v) and
then recrystallized from EtOAc and hexane to give a
white solid (2.4 g, 67% yield) (ꢀ)-29: mp 157–159 °C;
[a]D ꢀ5.5 (c = 1.1, CHCl3); 1H NMR (CDCl3,
400 MHz): d 7.41–7.09 (m, 25H), 6.91 (d, J = 1.6 Hz,
1H), 6.77 (m, 2H), 6.17 (s, 1H), 5.06 (s, 4H), 4.98 (s,
2H), 4.82 (AB, J = 11.9 Hz, 2H), 4.42 (d, J = 6.6 Hz,
1H), 4.05 (s, 2H), 3.91 (br, 1H), 2.93 (A of ABt,
J = 14.5, 3.2 Hz, 1H), 2.72 (B of ABt, 14.5, 8.5 Hz,
1H); 13C NMR (CDCl3, 400 MHz): d 156.4, 155.6,
155.3, 148.9, 148.8, 142.1, 137.2, 137.1, 137.0, 133.5,
128.6, 128.5, 128.4, 128.0, 127.8, 127.7, 127.6, 127.3,
127.2, 127.1, 126.7, 125.3, 119.9, 114.5, 113.6, 112.1,
111.2, 106.7, 90.9, 77.2, 76.7, 71.1, 70.9, 70.3, 70.2,
When ethanethiol was used instead of butanethiol, the
mixture was heated to 150 °C for 1.5 h while excess eth-
anethiol was distilled off in the first 10 min. The
reaction mixture was work up as the above procedure
to afford 56% of 27 and 11% 17. Compound 27 was
identified by mp 107–109 °C; 1H NMR (CDCl3,
400 MHz): d 7.36–7.23 (m, 15H), 6.25 (d, J = 2.2 Hz,
1H), 6.07 (d, J = 2.2 Hz, 1H), 4.96 (s, 2H), 4.92 (s,
2H), 3.99 (s, 2H); 13C NMR (CDCl3, 400 MHz): d
158.4, 157.9, 154.9, 140.7, 136.7, 136.6, 128.4, 128.2,
128.1, 127.8, 127.5, 127.3, 127.0, 125.6, 108.5, 94.7,
93.3, 70.2, 69.9, 28.3; HRMS (ESI) calcd for
C27H24O3Na (M+Na) 419.1623, found 419.1645.
4.3. (E)-3-[2,4-Bis(benzyloxy)-5-benzyl-6-hydroxyphen-
yl]-1-[3,4-bis(benzyloxy)phenyl]propene (28)
At rt under an N2 atmosphere, 25% H2SO4/SiO2 (1.6 g,
4 mmol) was added in one batch to the stirred mixture
of 2-benzyl-3,5-bis(benzyloxy)phenol (3.96 g, 10 mmol)
and (E)-3,4-bis(benzyloxy)cinnamyl alcohol (3.46 g,
10 mmol) in dry CH2Cl2 (80 mL). The resulting mixture
was stirred at rt overnight. After filtration and evapora-
tion, the residue was purified by column chromatogra-
phy on silica gel (EtOAc/n-hexane = 1/7 v/v) and
recrystalized from EtOAc and n-hexane to give a white
solid, (3.4 g, 46.0% yield): mp 93–95 °C; 1H NMR
(CDCl3, 400 MHz): d 7.41–7.22 (m, 30H), 6.92 (s, 1H),
6.79 (s, 1H), 6.78 (d, J = 4.0 Hz, 1H), 6.35 (A of AB,
J = 15.8 Hz, 1H), 6.26 (s, 1H), 6.13–6.07 (B of ABt,
J = 15.8, 5.0 Hz, 1H), 5.08 (s, 2H), 5.07 (s, 2H), 4.99
(s, 4H), 4.02 (s, 2H), 3.55 (d, J = 5.0 Hz, 2H); 13C
NMR (CDCl3, 400 MHz): d 156.1, 155.6, 154.0, 148.9,
148.2, 141.1, 137.2, 137.1, 131.0, 130.1, 128.5, 128.4,

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S. B. Wan et al. / Bioorg. Med. Chem. 13 (2005) 2177–2185
29.1, 26.8; HRMS (ESI) calcd for C50H46O7Na (M+Na)
781.3141, found 781.3110.
4.7. (+)-(2S,3S)-cis-5,7-Bis(benzyloxy)-8-benzyl-2-[3,4-
bis-(benzyloxy)phenyl]chroman-3-ol ((+)-32)
4.5. (ꢀ)-(2S,3R)-trans-5,7-Bis(benzyloxy)-8-benzyl-2-
[3,4-bis-(benzyloxy)phenyl]chroman-3-ol ((ꢀ)-30)
Under an N2 atmosphere, the ketone (ꢀ)-31 (700 mg,
0.95 mmol) was dissolved in dry THF (15 mL), and
the solution was cooled to ꢀ78 °C. Then L-Selectride
(1.5 mL, 1 M solution in THF, 1.5 mmol) was added
dropwise. The resulting solution was stirred at
ꢀ78 °C for 8 h. 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 chromatography on silica gel (5%
EtOAC/benzene) and then recrystallized with ethanol
and EtOAC to afford the desired product (630 mg,
90%) as a white solid: mp 129–131 °C, [a]D +5.3
(c = 1.2, CHCl3); 1H NMR (CDCl3, 400 MHz): d
7.44–7.07 (m, 25H), 7.05 (s, 1H), 6.93 (AB,
J = 8.4 Hz, 2H), 6.26 (s, 1H), 5.15 (s, 2H), 5.02 (s,
2H), 5.00 (s, 4H), 4.92 (br s, 1H), 4.20 (br s, 1H),
4.10 (AB, J = 14.5 Hz, 2H), 3.07 (A of AB,
J = 17.2 Hz, 1H), 2.92 (B of ABt, J = 17.2, 4.2 Hz,
1H); 13C NMR (CDCl3, 400 MHz): d 156.2, 155.9,
152.8, 148.9, 148.5, 142.1, 137.2, 137.1, 137.0, 131.6,
128.5, 128.4, 128.0, 127.8, 127.7, 127.4, 127.2, 125.2,
118.9, 114.9, 112.9, 110.2, 101.1, 91.4, 78.0, 71.2,
71.0, 70.5, 70.0, 66.1, 28.6, 28.2; HRMS (ESI) calcd
for C50H44O6Na (M+Na) 763.3036 found 763.3024.
To a suspension of (ꢀ)-29 (2.4 g, 3.1 mmol) in 1,2-
dichloroethane (50 mL) was added triethyl orthofor-
mate (1 mL), followed by PPTS (450 mg, 1.8 mmol).
The mixture was stirred at rt for 20 min until the solid
dissolved. The mixture was then heated to 55 °C for
5 h until TLC showed the reaction had been completed.
After evaporation of the solvent, the residue was dis-
solved in DME (30 mL) and MeOH (30 mL), K2CO3
(450 mg) was added. The mixture was stirred at rt over-
night. After evaporation of the solvent, the residue was
purified by flash chromatography on silica gel (EtOAc/
hexane, 1/3 v/v) to afford the desired product as white
solid (1.8 g, 77% yield): mp 145–146 °C; [a]D ꢀ20.1
(c = 1.3, CHCl3); 1H NMR (CDCl3, 400 MHz): d
7.42–7.15 (m, 25H), 6.93 (d, J = 1.6 Hz, 1H), 6.88 (A
of AB, J = 8.3 Hz, 1H), 6.82 (B of ABt, J = 8.3,
1.6 Hz, 1H), 6.24 (s, 1H), 5.13 (s, 2H), 5.02 (s, 2H),
5.00 (s, 2H), 4.98 (s, 2H), 4.63 (d, J = 8.1 Hz, 1H),
4.04 (AB, J = 14.2 Hz, 2H), 3.86 (m, 1H), 3.10 (A of
ABt, J = 5.6, 16.4 Hz, 1H), 2.67 (B of ABt, J = 9.0,
16.4 Hz, 1H); 13C NMR (CDCl3, 400 MHz): d 155.8,
155.5, 152.9, 148.9, 148.8, 142.2, 137.2, 137.1, 137.0,
136.9, 131.2, 128.7, 128.5, 128.4, 128.3, 127.9, 127.8,
127.7, 127.4, 127.2, 127.1, 127.0, 125.2, 120.2, 114.5,
113.2, 110.2, 102.4, 91.1, 81.2, 71.1, 70.9, 70.4, 69.9,
68.2, 28.6, 27.6. HRMS (ESI) calcd for C50H44O6Na
(M+Na) 763.3036, found 763.3032.
4.8. (+)-(2S,3S)-5,7-Bis(benzyloxy)-8-benzyl-2-[3,4-bis-
(benzyloxy)-phenyl]chroman-3-yl 3,4,5-tris(benzyloxy)-
benzoate ((+)-33)
4.6. (+)-(2R)-5,7-Bis(benzyloxy)-8-benzyl-2-[3,4-bis(benz-
yloxy)-phenyl]chroman-3-one ((ꢀ)-31)
Under an N2 atmosphere, a solution of 3,4,5-tris(benzyl-
oxy)benzoic acid (170 mg, 0.39 mmol) was refluxed with
oxally chloride (1 mL) in dry CH2Cl2 (10 mL) and one
drop of DMF for 3 h. The excess oxally chloride and
solvent were removed by distillation and the residue
was dried under vacuum for 3 h and dissolved in CH2Cl2
(2 mL). This solution was added dropwise to a solution
of (+)-32 (150 mg, 0.20 mmol) and DMAP (75 mg,
0.62 mmol) in CH2Cl2 (15 mL) at 0 °C. The mixture
was stirred at rt overnight, then saturated NaHCO3
aqueous solution was added. The organic layer was sepa-
rated, and the aqueous layer was extracted with CH2Cl2.
The organic phases were combined, dried (MgSO4) and
evaporated. The residue was purified by flash chroma-
tography on silica gel (5% EtOAc/benzene) to afford
the desired compound (215 mg, 91%). Recrystallization
in CHCl3 and ether gave a white powder: mp 52–
Dess–Martin periodinane (6.3 mL, 15% g/mL in
CH2Cl2, 2.2 mmol) was added in one batch to a stirred
solution of (ꢀ)-30 (900 mg, 1.2 mmol) in CH2Cl2
(30 mL) under an N2 atmosphere. The mixture was stir-
red 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 ex-
tracted 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 de-
sired compound (770 mg, 86%): mp 143–145 °C, [a]D
1
ꢀ17.1 (c = 1.1, CHCl3); H NMR (CDCl3, 400 MHz):
1
d
7.43–7.07 (m, 25H), 6.89 (s, 1H), 6.84 (AB,
54 °C; [a]D +37.5 (c = 1.0, CHCl3); H NMR (CDCl3,
J = 8.5 Hz, 2H), 6.33 (s, 1H), 5.13–5.04 (m, 6H), 5.02
(s, 1H), 4.99 (s, 2H), 4.05 (AB J = 14.2 Hz, 2H), 3.67
(AB, J = 20.8 Hz, 2H); 13C NMR (CDCl3, 400 MHz):
d 205.8, 156.5, 154.8, 152.5, 149.0, 148.7, 141.7, 137.1,
136.9, 136.8, 136.5, 128.6, 128.5, 128.4, 128.1, 128.0,
127.8, 127.7, 127.3, 127.1, 125.4, 120.0, 114.5, 113.2,
111.9, 102.4, 92.6, 82.9, 71.0, 70.5, 70.2, 34.0, 28.8;
HRMS (ESI) calcd for C50H42O6Na (M+Na)
761.2879, found 761.2843.
400 MHz): d 7.39–7.10 (m, 42H), 6.99 (t, J = 7.4 Hz,
1H), 6.93 (AB, J = 8.3 Hz, 2H), 6.31 (s, 1H), 5.65 (br
s, 1H), 5.13 (br s, 1H), 5.07 (s, 2H), 5.02 (s, 4H), 5.00
(s, 2H), 4.92 (s, 4H), 4.83 (AB, J = 11.8 Hz, 2H), 4.11
(s, 1H), 3.15 (br s, 1H); 13C NMR (CDCl3, 400 MHz):
d 165.2, 156.0, 155.9, 153.2, 152.3, 148.8, 148.6, 142.6,
142.2, 137.4, 137.2, 137.0, 136.5, 131.4, 128.7, 128.6,
128.5, 128.4, 128.2, 128.0, 127.9, 127.7, 127.3, 127.2,
125.4, 125.1, 119.4, 114.6, 113.2, 110.3, 109.2, 101.0,

S. B. Wan et al. / Bioorg. Med. Chem. 13 (2005) 2177–2185
2183
91.2, 75.1, 71.1, 70.5, 70.0, 68.6, 28.7, 26.2; HRMS (ESI)
calcd for C78H66O10Na (M+Na) 1185.4554, found
1185.4542.
239–241 °C (decomposed); [a]D ꢀ35 (c = 2.0, acetone);
1H NMR (acetone-d6, 400 MHz): d 7.44 (d, J = 7.1 Hz,
2H), 7.33 (t, J = 7.5 Hz, 2H), 7.23 (s, 2H), 7.21 (t,
J = 7.3 Hz, 1H), 6.92–6.86 (m, 2H), 6.34 (s, 1H), 5.56
(m, 1H), 5.35 (d, J = 6.2 Hz, 1H), 4.17 (AB,
J = 14.3 Hz, 2H), 3.12 (A of ABt, J = 16.5, 5.2 Hz,
1H), 2.98 (B of ABt, J = 16.5. 6.2 Hz, 1H); 13C NMR
(acetone-d6, 400 MHz): d 165.0, 154.1, 153.7, 152.8,
144.9, 144.7, 144.6, 142.2, 137.8, 130.2, 128.3, 127.5,
124.8, 120.5, 117.9, 114.8, 113.2, 108.8, 106.2, 98.2,
95.1, 77.7, 69.4, 23.5; HRMS (ESI) calcd for
C29H24O10Na 555.1267, found 555.1285.
4.9. (ꢀ)-(2S,3R)-5,7-Bis(benzyloxy)-8-benzyl-2-[3,4-bis-
(benzyloxy)phenyl]chroman-3-yl 3,4,5-tris(benzyloxy)-
benzoate ((ꢀ)-34)
Following the procedure used for the preparation of
(ꢀ)-33 but with (ꢀ)-30 as starting material, (ꢀ)-
(2S,3R)-5,7-bis(benzyloxy)-8-benzyl-2-[3,4-bis(benzyl-
oxy)phenyl]chroman-3-yl 3,4,5-tris(benzyloxy)benzoate
was obtained (90% yield) as a white solid: mp 103–
1
105 °C, [a]D ꢀ9.8 (c = 1.3, CHCl3); H NMR (CDCl3,
4.12. (E)-3-[2,4-Bis(benzyloxy)-6-hydroxyphenyl]-1-[3-
benzyloxyphenyl]propene (9d)
400 MHz): d 7.37–7.11 (m, 42H), 6.90 (s, 1H), 6.77 (m,
2H), 6.27 (s, 1H), 5.42 (m, 1H), 5.18 (d, J = 6.3 Hz,
1H), 5.06 (s, 4H), 5.05–4.99 (m, 4H), 4.97 (s, 4H), 4.88
(s, 2H), 4.12 (AB, J = 14.1 Hz, 2H), 3.01 (A of ABt,
J = 16.8, 5.0 Hz, 1H), 2.89 (B of ABt, J = 16.8, 6.4 Hz,
1H); 13C NMR (CDCl3, 400 MHz): d 156.0, 155.9,
155.4, 152.5, 152.3, 148.8, 148.6, 142.3, 142.1, 137.3,
137.1, 137.0, 136.9, 136.5, 131.3, 128.7, 128.5, 128.4,
128.3, 128.1, 128.0, 127.9, 127.8, 127.7, 127.5, 127.3,
127.2, 127.1, 125.3, 124.9, 114.6, 112.8, 110.2, 108.9,
101.5, 91.0, 78.0, 75.0, 71.2, 71.1, 71.0, 70.4, 70.0, 69.9,
28.6, 24.0; HRMS (ESI) calcd for C78H66O10Na
(M+Na) 1185.4554, found 1185.4573.
At ꢀ20 °C under an N2 atmosphere, di-isopropyl azo-
carboxylate (3.03 g, 15 mmol) was added to a solution
of (E)-3-benzyloxycinnamyl alcohol (2.4 g, 10 mmol),
3,5-bis(benzyloxy)phenol (3.06 g, 10 mmol) and triphen-
ylphosphine (3.93 g, 15 mmol) in dry toluene (100 mL).
The mixture was stirred for 1 h, ꢀ5 to ꢀ20 °C. After
evaporation, the residue was purified by chromatogra-
phy on silica gel (benzene) to give the desired compound
1
as a white solid 3.19 g (60% yield): mp 82–84 °C; H
NMR (CDCl3, 400 MHz): d 7.42–7.30 (m, 15H), 7.19–
7.15 (t, 7.9 Hz, 1H), 6.93–6.89 (m, 2H), 6.79 (dd,
J = 7.9, 2.2 Hz, 1H), 6.43 (A of AB, J = 15.9 Hz, 1H),
6.33 (B of ABt, J = 15.9, 5.6 Hz, 1H), 6.26 (d,
J = 2.3 Hz, 1H), 6.14 (d, J = 2.3 Hz, 1H), 5.17 (s, 1H),
5.01 (s, 2H), 5.00 (s, 2H), 4.97 (s, 2H), 3.57–3.56 (d,
J = 5.6 Hz, 2H); 13C NMR (CDCl3, 400 MHz): d 158.7,
158.5, 157.7, 155.4, 138.6, 136.8, 136.7, 130.0, 129.2,
128.6, 128.4, 128.3, 128.2, 127.8, 127.7, 127.6, 17.3,
127.2, 127.1, 118.9, 113.4, 112.1, 106.7, 94.8, 93.4, 70.1,
69.9, 69.7, 26.2; HRMS (ESI) calcd for C36H32O4Na
(M+Na) 551.2198, found 551.2187.
4.10. (+)-(2S,3S)-5,7-Dihydroxy-8-benzyl-2-[3,4-dihy-
droxy-phenyl]chroman-3-yl 3,4,5-trihydroxybenzoate
((+)-15)
Under an H2 atmosphere, Pd(OH)2/C (20%, 400 mg)
was added to a solution of (+)-33 (200 mg, 0.17 mmol)
in a solvent mixture of THF/MeOH (1:1 v/v, 20 mL).
The reaction mixture was stirred at rt under H2 for 6 h
when TLC showed that the reaction was completed.
The reaction mixture was filtered to remove the catalyst.
The filtrate was evaporated, and the residue was rapidly
purified by flash chromatograph on silica gel
(10%MeOH/CH2Cl2, then 20% MeOH/CH2Cl2) to
afford (+)-8-benzylcatechin gallate ((+)-16) (82 mg,
90% yield): mp 243–245 °C (decomposed); [a]D +123
4.13. (E)-3-[2,4-Bis(benzyloxy)-6-hydroxyphenyl]-1-phen-
ylpropene (19e)
Following the procedure of the preparation of 19d, cinn-
amyl alcohol was used as starting material to yield 19e as
a white solid (62% yield); mp 76–78 °C; 1H NMR
(CDCl3, 400 MHz): d 7.40–7.24 (m, 15H), 6.48 (A of
AB, J = 15.9 Hz, 1H), 6.35 (B of ABt, J = 15.9, 5.5 Hz,
1H), 6.27 (d, J = 2.1 Hz, 1H), 6.16 (d, J = 2.1 Hz, 1H),
5.07 (s, 1H), 5.02 (s, 2H), 4.99 (s, 2H), 3.59–3.57 (d,
J = 5.5 Hz, 2H); 13C NMR (CDCl3, 400 MHz): d 158.5,
157.6, 155.4, 137.0, 136.8, 136.6, 130.2, 128.3, 128.2,
128.1, 128.0, 127.8, 127.6, 127.3, 127.0, 126.8, 125.8,
106.6, 94.8, 93.4, 70.1, 69.9, 26.2; HRMS (ESI) calcd
for C29H26O3Na (M+Na) 445.1780, found 445.1793.
1
(c = 1.8, acetone); H NMR (acetone-d6, 400 MHz): d
7.53 (d, J = 7.4 Hz, 2H), 7.42 (t, J = 7.6 Hz, 2H), 7.26–
7.21 (m, 4H), 7.04 (AB, J = 8.2 Hz, 2H), 6.31 (s, 1H),
5.75 (br s, 1H), 5.32 (br s, 1 H), 4.22 (AB, J = 14.3 Hz,
2H), 3.29 (A of ABt, J = 17.4, 4.4 Hz, 1H), 3.17 (B of
AB, J = 17.4 Hz, 1H); 13C NMR (acetone-d6,
400 MHz): d 165.2, 154.2, 154.1, 153.6, 144.9, 144.6,
144.3, 142.6, 137.9, 130.6, 128.4, 127.8, 125.0, 120.9,
118.1, 114.7, 113.7, 109.1, 106.7, 98.0, 95.3, 77.1, 68.3,
25.9; HRMS (ESI) calcd for C29H24O10Na (M+Na)
555.1267, found 555.1279.
4.14. (+)-(1S,2S)-3-[2,4-Bis(benzyloxy)-6-hydroxyphen-
yl]-1-3-benzyloxyphenylpropane-1,2-diol ((+)-22d)
4.11. (ꢀ)-(2S,3R)-5,7-Dihydroxy-8-benzyl-2-[3,4-dihy-
droxyphenyl]chroman-3-yl 3,4,5-trihydroxybenzoate
((ꢀ)-16)
Following the procedure used for the preparation of
(ꢀ)-29 but with 19d as starting material and AD-mix-a
as dihydroxylation regent, ((+)-22d) was obtained
(63% yield) as a white solid; mp 120–122 °C; [a]D +4.4
(c = 0.5, CHCl3); 1H NMR (CDCl3, 400 MHz): d
7.31–7.20 (m, 14H), 7.07–7.04 (m, 3H), 6.90 (s, 1H),
Following the procedure for the preparation (+)-15, but
with (ꢀ)-33 as starting material, (ꢀ)-8-benzyl epi-cate-
chin gallate ((ꢀ)-16) was obtained (91% yield): mp

2184
S. B. Wan et al. / Bioorg. Med. Chem. 13 (2005) 2177–2185
6.81 (m, 2H), 6.18 (s, 1H), 6.13 (s, 1H), 4.87 (s, 4H), 4.77
(s, 2H), 4.38 (d, J = 6.1 Hz, 1H), 3.94 (m, 1H), 2.87 (A of
AB, J = 14.2, 1H), 2.71 (B of ABt, J = 14.2, 8.8 Hz, 1H);
13C NMR (CDCl3, 400 MHz): d 158.9, 158.7, 157.7,
157.1, 141.9, 136.8, 136.7, 129.5, 128.5, 128.4, 127.9,
127.6, 127.5, 127.4, 126.7, 119.2, 114.5, 113.2, 106.1,
95.7, 93.3, 76.7, 69.9, 69.8, 26.5; HRMS (ESI) calcd
for C36H34O6Na (M+Na) 585.2253, found 585.2293.
118.6, 114.2, 112.9, 110.9, 94.6, 94.0, 78.4, 70.0, 69.9,
69.8, 66.3, 28.2; HRMS (ESI) calcd for C36H32O5Na
(M+Na) 567.2147, found 567.2128.
Using the same procedure, (ꢀ)-22d was used as starting
material to afford (ꢀ)-25d with opposite configuration
and identical NMR spectra as the (+)-isomer.
4.17. (+)-(2S,3S)-cis-5,7-Bis(benzyloxy)-2-phenylchro-
man-3-ol ((+)-25e)
Using the same procedure, AD-mix-b was used to afford
(ꢀ)-22d with opposite configuration and identical NMR
spectra as the (+)-isomer.
Following the procedure used for the preparation of (+)-
25d, but with (+)-22e as starting material, (+)-25e was
obtained (47% yield) as a white solid; mp 60–62 °C;
[a]D +0.9 (c = 1.0, ethyl acetate); 1H NMR (CDCl3,
400 MHz): d 7.49–7.30 (m, 15H), 6.29 (d, J = 2.2 Hz,
1H), 6.27 (d, J = 2.2 Hz, 1H), 5.02 (br s, 1H), 4.99 (s,
4H), 4.25 (br s, 1H), 3.03 (A of ABt, J = 17.2, 1.4 Hz,
1H), 2.96 (B of ABt, J = 17.2, 4.2 Hz, 1H); 13C NMR
(CDCl3, 400 MHz): d 158.7, 158.2, 155.2, 138.1, 136.9,
136.8, 128.5, 128.4, 128.0, 127.9, 127.8, 127.4, 127.1,
126.2, 100.9, 94.6, 94.0, 78.6, 70.0, 69.8, 66.2, 28.2;
HRMS (ESI) calcd for C29H26O4Na (M+Na)
461.1729, found 461.1741.
4.15. (+)-(1S,2S)-3-[2,4-Bis(benzyloxy)-6-hydroxyphen-
yl]-1-phenylpropane-1,2-diol ((+)-22e)
Following the procedure used for the preparation of
(ꢀ)-29 but with 19e as starting material and AD-mix-a
as dihydroxylation regent, (+)-22e was obtained (47%
yield) as a white solid; mp 121–123 °C; [a]D +4.7
(c = 0.6, CHCl3); 1H NMR (CDCl3, 400 MHz): d
7.38–7.19 (m, 13H), 7.10 (m, 2H), 6.23 (d, J = 2.3 Hz,
1H), 6.17 (d, J = 2.3 Hz, 1H), 4.94 (s, 2H), 4.82 (AB,
J = 11.7 Hz, 2H), 4.47 (d, J = 6.6 Hz, 1H), 3.97 (m,
1H), 2.88 (A of ABt, J = 14.6, 3.6 Hz, 1H), 2.72 (B of
ABt, J = 14.6, 8.6 Hz, 1H); 13C NMR (CDCl3,
400 MHz): d 158.8, 157.6, 157.0, 140.0, 136.6, 136.5,
128.3, 128.2, 128.1, 128.0, 127.7, 127.4, 127.3, 126.8,
126.5, 105.9, 95.6, 93.2, 76.6, 69.8, 69.7, 26.2; HRMS
(ESI) calcd for C29H28O5Na (M+Na) 479.1834, found
479.1841.
4.18. (+)-(2S,3S)-5,7-Bis(benzyloxy)-2-(3-benzyloxyphen-
yl)chroman-3-yl 3,4,5-tris(benzyloxy)benzoate ((+)-35)
Following the procedure used for the preparation of (+)-
33 but with (+)-25d as starting material, (+)-35 was ob-
tained (80% yield) as a white solid: mp 107–109 °C, [a]D
1
+65.1 (c = 1.3, CHCl3); H NMR (CDCl3, 400 MHz): d
4.16. (+)-(2S,3S)-cis-5,7-Bis(benzyloxy)-2-(3-benzyloxy-
phenyl)chroman-3-ol ((+)-25d)
7.41–7.17 (m, 31H), 7.12 (s, 1H), 6.99 (d, J = 7.4 Hz,
1H), 6.86 (d, J = 6.8 Hz, 1H), 6.39 (s, 1H), 6.31 (s,
1H), 5.62 (br s, 1H), 5.14 (br s, 1H), 5.02 (s, 4H), 5.01
(s, 4H), 4.99 (s, 2H), 4.84 (AB, J = 11.4 Hz, 2H), 3.11
(br s, 2H); 13C NMR (CDCl3, 400 MHz): d 164.8,
158.5, 157.7, 155.2, 152.0, 139.1, 137.2, 136.6, 136.5,
136.2, 129.2, 128.4, 128.3, 128.2, 128.1, 127.9, 127.7,
127.6, 127.4, 127.2, 126.9, 124.7, 118.8, 114.1, 113.0,
108.7, 100.6, 94.4, 93.6, 77.3, 74.8, 70.7, 69.9, 69.7,
69.6, 68.4, 25.7; HRMS (ESI) calcd for C64H54O9Na
(M+Na) 989.3666, found 989.3633.
To a suspension of (1S,2S)-3-[2,4-bis(benzyloxy)-6-
hydroxyphenyl]-1-phenylpropane-1,2-diol (360 mg, 0.79
mmol) in 1,2-dichloroethane (10 mL) was added triethyl
orthoformate (170 mg, 1.6 mmol), followed by PPTS
(118 mg, 0.47 mmol). The mixture was stirred at rt for
20 min and the solid dissolved, and then evaporated
the solvent under vacuum. The residue was dissolved
in dry CH2Cl2 (10 mL), the solution was cooled to ꢀ5
to 0 °C, and AcBr (145 mg, 112 mmol) was added drop-
wise. The mixture was stirred at ꢀ5 to 0 °C for 45 min,
distilled the solvent under vacuum. Acetone (15 mL)
and K2CO3 (160 mg) were added successively. After
the mixture was stirred at rt for 6 h, methanol (15 mL)
and another batch of K2CO3 (160 mg) were added. Then
the mixture was stirred at rt overnight. After evaporating
the solvent, water (30 mL) was added, extracted with
CH2Cl2, the combined organic phases was dried
(MgSO4) and solvent was distilled under vacuum. The
residue was purified by chromatograph on silica gel (n-
hexane/EtOAc = 3/1 v/v), then recrystallized to give a
white solid 170 mg (49%); mp 85–87 °C; [a]D +37.4
Using the same procedure, (ꢀ)-25 was used as starting
material to afford (ꢀ)-35 with opposite configuration
and identical NMR spectra as the (+)-isomer.
4.19. (+)-(2S,3S)-5,7-Bis(benzyloxy)-2-(3-benzyloxyphen-
yl)chroman-3-yl 3,4,5-tris(benzyloxy)benzoate ((+)-36)
Following the procedure used for the preparation of
(+)-33 but with (+)-25e as starting material, (+)-36 was
obtained (82% yield) as a white solid: mp 130–132 °C,
[a]D +2.9 (c = 1.5, CHCl3); 1H NMR (CDCl3,
400 MHz): d 7.39–7.24 (m, 30H), 7.19 (s, 2H), 6.39 (d,
J = 2.2 Hz, 1H), 6.31 (d, J = 2.2 Hz, 1H), 5.60 (br s,
1H), 5.16 (br s, 1H), 5.07 (s, 2H), 5.03 (s, 2H), 5.02 (s,
2H), 5.01 (s, 2H), 4.99 (s, 2H), 3.10 (br s, 2H); 13C
NMR (CDCl3, 400 MHz): d 164.9, 158.5, 157.7, 155.3,
152.0, 142.0, 137.5, 137.1, 136.6, 136.5, 136.3, 128.4,
128.3, 128.2, 128.0, 127.9, 127.8, 127.7, 127.6, 127.2,
126.9, 126.2, 124.7, 108.7, 100.6, 94.3, 93.6, 77.4, 74.8,
1
(c = 1.1, ethyl acetate); H NMR (CDCl3, 400 MHz): d
7.45–7.31 (m, 16H), 7.18 (br s, 1H), 7.08 (d,
J = 7.3 Hz, 1H), 6.96 (d, J = 7.5 Hz, 1H), 6.30 (d,
J = 6.7 Hz, 2H), 5.08 (s, 2H), 5.00 (s, 4H), 4.79 (br s,
1H), 4.26 (br s, 1H), 3.05 (AB, J = 17.2 Hz, 2H); 13C
NMR (CDCl3, 400 MHz): d 159.0, 158.7, 158.2, 155.1,
139.8, 136.8, 129.6, 128.5, 127.9, 127.8, 127.5, 127.1,

S. B. Wan et al. / Bioorg. Med. Chem. 13 (2005) 2177–2185
2185
70.7, 69.9, 69.7, 68.5, 25.7; HRMS (ESI) calcd for
C57H48O8Na (M+Na) 883.3247, found 883.3212.
mittee of the Hong Kong Special Administrative
Region, China (to T.H.C., Project No. AoE/P-10/01),
and research grants from the National Cancer Insti-
tute—National Institutes of Health and Barbara Ann
Karmanos Cancer Institute Prevention Program (to
Q.P.D.), T.H.C. acknowledges the support of McGill
University for the granting of a leave.
4.20. (+)-(2S,3S)-5,7-Dihydroxy-2-(3-hydroxyphenyl)-
chroman-3-yl 3,4,5-trihydroxybenzoate ((+)-12)
Following the procedure for the preparation (+)-15, but
with (+)-35 as starting material, compound (+)-12 was
obtained (90% yield): mp 251–253 °C (decomposed);
[a]D +141 (c = 3.5, ethanol); 1H NMR (acetone-d6,
400 MHz): d 7.31–7.19 (m, 3H), 7.18 (s, 2H), 6.89 (dd,
J = 8.0, 1.7 Hz, 1H), 6.24 (s, 1H), 6.23 (s, 1H), 5.76 (br
s, 1H), 5.37 (br s, 1H), 3.26 (A of ABt, J = 17.4,
4.6 Hz, 1H), 3.13 (B of ABt, J = 17.4, 1.8 Hz, 1H); 13C
NMR (acetone-d6, 400 MHz): d 164.9, 156.7, 156.4,
156.1, 155.6, 144.6, 140.0, 137.4, 128.7, 120.5, 117.4,
114.2, 113.2, 108.7, 97.7, 76.9, 68.1, 25.406; HRMS
(ESI) calcd for C22H18O9Na (M+Na) 449.0849, found
449.0833.
References and notes
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Using the same procedure, (ꢀ)-35 was used as starting
material to afford (ꢀ)-13 with opposite configuration
and identical NMR spectra as the (+)-isomer.
4.21. (+)-(2S,3S)-5,7-Dihydroxy-2-phenylchroman-3-yl
3,4,5-trihydroxybenzoate ((+)-14)
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Following the procedure for the preparation (+)-15, but
with (+)-36 as starting material, compound (+)-14 was
obtained (90% yield): mp 258–260 °C (decomposed);
[a]D +13.9 (c = 3.5, ethanol); 1H NMR (acetone-d6,
400 MHz): d 7.73–7.71 (m, 2H), 7.49–7.45 (m, 2H),
7.41–7.38 (m, 1H), 7.17 (s, 2H), 6.24 (d, J = 2.2 Hz,
1H), 6.23 (d, J = 2.2 Hz, 1H), 5.76 (br s, 1H), 5.44 (br
s, 1H), 3.27 (A of ABt, J = 17.4, 4.5 Hz, 1H), 3.14 (B
of ABt, J = 17.4, 1.4 Hz, 1H); 13C NMR (acetone-d6,
400 MHz): d 164.7, 156.6, 156.3, 155.7, 144.7, 138.5,
137.6, 127.6, 127.3, 126.3, 120.4, 108.7, 97.7, 95.4,
94.6, 77.0, 68.1, 25.3; HRMS (ESI) calcd for
C22H18O8Na (M+Na) 433.0899, found 433.0904.
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Med. Chem. 2004, 12, 3521.
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Acknowledgements
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This work was supported by the Areas of Excellence
Scheme established under the University Grants com-