Ginkgolides and Glycine Receptors: A Structure-Activity Relationship Study

Article abstract of DOI:10.1002/chem.200305473

Ginkgolides from the Ginkgo biloba tree are diterpenes with a cage structure consisting of six five-membered rings and a unique tBu group. They exert a variety of biological properties. In addition to being antagonists of the platelet activating factor receptor (PAFR), it has recently been shown that native ginkgolides are potent and selective antagonists of the inhibitory glycine receptor. Forty new ginkgolide derivatives have been prepared in good to high yields on milligram scales and investigated for their antagonistic properties at homomeric α1 glycine receptors, thus providing the first structure-activity relationship study of ginkgolides at glycine receptors. A high-throughput screening assay showed that native ginkgolide C was the most potent ligand, and that manipulation of any of the hydroxyl groups led to loss of activity at α1 glycine receptors.

Full text of DOI:10.1002/chem.200305473

FULL PAPER
Ginkgolides and Glycine Receptors: A Structure Activity Relationship Study
Stanislav Jaracz,[a] Koji Nakanishi,*[a] Anders A. Jensen,[b] and Kristian Str˘mgaard*[b]
Abstract: Ginkgolides from the Ginkgo
biloba tree are diterpenes with a cage
structure consisting of six five-mem-
bered rings and a unique tBu group.
They exert a variety of biological prop-
erties. In addition to being antagonists
of the platelet activating factor recep-
tor (PAFR), it has recently been shown
that native ginkgolides are potent and
selective antagonists of the inhibitory
glycine receptor. Forty new ginkgolide
derivatives have been prepared in good
to high yields on milligram scales and
investigated for their antagonistic prop-
erties at homomeric a1 glycine recep-
tors, thus providing the first structure
activity relationship study of ginkgo-
lides at glycine receptors.
A high-
throughput screening assay showed
that native ginkgolide C was the most
potent ligand, and that manipulation of
any of the hydroxyl groups led to loss
of activity at a1 glycine receptors.
Keywords: inhibitors
chemistry natural products
rearrangement ¥ terpenoids
¥ medicinal
¥
¥
Introduction
that the flavonoids act as antioxidants, while the terpene tri-
lactones are involved in anti-inflammation and prevention
of blood clotting associated with the antagonistic activity at
the platelet-activating factor (PAF) receptor.[6] However, the
neuroprotective effects of EGb761 have so far not been as-
sociated with specific components of the extract.[7,8]
The terpene trilactones, ginkgolides (Figure 1) and biloba-
lide, are unique components of EGb761, the structures of
which were elucidated in 1967.[9 15] The ginkgolides are diter-
pene trilactones with a cage-like skeleton consisting of six
five-membered rings, that is, a spiro[4.4]nonane carbocyclic
ring, three lactones, and a tetrahydrofuran moiety. Terpene
trilactones from G. biloba are also among the very few natu-
ral products containing a tBu group.
The Ginkgo biloba tree is among the oldest living plants
and is thus referred to as a ™living fossil∫. It is admired for
its unique beauty, especially its leaves, which have been ex-
emplified by a poem by Johann Wolfgang von Goethe from
1815.[1] The Ginkgo tree has a long history of use in tradi-
tional Chinese medicine, but it was not until the 1960s that a
standardized extract of G. biloba leaves, EGb761, was intro-
duced into the European markets.[2] Today the G. biloba ex-
tract is one of the most popular botanical medicines world-
wide.
Numerous beneficial effects of EGb761 have been postu-
lated including improving peripheral vascular function, in-
hibition of thrombosis and embolism, neuroprotection in
Alzheimer×s disease and cognitive disorders, anti-inflamma-
tory and antiproliferative activities, as well as antioxidant
activities.[3] EGb761 is a complex mixture of compounds,
the main ingredients being flavonoids and terpene trilac-
tones (ginkgolides and bilobalide) that comprise 24 and 6%,
respectively, of the total extract.[4,5] It has been proposed
Figure 1. Ginkgolides A, B, C, J, and M.
[a] S. Jaracz, Prof. K. Nakanishi
In contrast to many studies on the neuroprotective effects
of EGb761, the ginkgolides have not been extensively stud-
ied, partly due to limited availability of pure ginkgolides.
The discovery in 1985 that ginkgolideB (GB, 2) was a
potent antagonist of the PAF receptor (PAFR)[16,17] led to
extensive structure activity relationship (SAR) studies on
Department of Chemistry, Columbia University
3000 Broadway MC3114, New York, NY 10027 (USA)
Fax : (+1)212-932-8273
E-mail: kn5@columbia.edu
[b] Prof. A. A. Jensen, Prof. K. Str˘mgaard
Department of Medicinal Chemistry
The Danish University of Pharmaceutical Sciences
Universitetsparken 2, 2100 Copenhagen (Denmark)
Fax : (+45)-3530-6040
28]
this receptor.[18 However, the significance of these effects
in relation to the neuroprotective effects of EGb761 is not
E-mail: krst@dfuni.dk
clear yet.[29]
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DOI: 10.1002/chem.200305473
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FULL PAPER
The first indication of a direct interaction of ginkgolides
with important targets in the brain was discovered when
ginkgolides were shown to be potent and highly selective
eral atoms away from the ginkgolide itself (Figure 2). Al-
though many hydroxyl group esterifications were performed
on this system, it was concluded that reactivity and selectivi-
ty were both lower as compared with the same reactions in
solution-phase; namely, the cleaved products were mixtures
of the starting materials, desired products and over-esteri-
fied products. Hence, the solid-phase approach was aban-
doned and preparation of a ginkgolide library was per-
formed via a similar approach but in solution.
32]
antagonists of the inhibitory glycine receptor (GlyR).[30
The GlyR is a ligand-gated ion channel found primarily in
the spinal cord and brain stem but also in higher brain re-
gions such as the hippocampus and developing cortex, which
consists of a1 a4 and b subunits.[33] Only a few ligands for
GlyRs have been available, the classical example being the
convulsant strychnine, a competitive antagonist. However,
since the neuropharmacology and functional importance of
GlyRs in higher brain regions is not well characterized,[34]
new potent and selective ligands are needed for further in-
vestigations of the GlyR.
The aim of this study was to prepare various ether-, ester-
and carbamoyl-derivatives of ginkgolide C by selective deri-
vatization of the hydroxyl groups. In the following we de-
scribe the synthesis of forty derivatives of ginkgolide C. The
ginkgolide derivatives thus prepared were then evaluated
for their antagonistic activity of the GlyR by means of a
fluorescence-based high-throughput screening assay.
Figure 2. Ginkgolide C attached to Wang resin via 10-benzyloxy group.
In the first step, GC (3) was selectively alkylated at 10-
OH with various benzyl-derived halides under mild reaction
Results and Discussion
conditions to form 6, 7, and 8 in 94 97% yield
(Scheme 1).[23,38] Hydrogen bonding between 1-OH and 10-
OH as described by Corey[35] is responsible for enhanced re-
activity of these hydroxyl groups. Thus, reaction with alkyl
bromides in DMF with K2CO3 as a base yields mixture of
10-O and 1-O monoalkylates, generally within less than 2 h.
Further alkylation does not occur even after several days of
stirring. The 10-OH/1-OH selectivity seems to be influenced
by the size of the incoming alkyl group. While benzyl-de-
rived halides provide GC benzyl ethers in the ratio of 10:1
to 15:1, methyl iodide yields methyl ethers under identical
conditions with only 1.7:1 selectivity.[39] Furthermore, mix-
tures of the monoalkyl ethers could not be separated by
silica gel chromatography; attempts to separate them by re-
crystallization also failed.
In the present study ginkgolide C (GC, 3) was chosen as the
starting material because it carries the most hydroxyl groups
of the ginkgolides, thus providing possibilities for more di-
verse library. Secondly, GC (3), together with GB (2), is the
most potent GlyR antagonist amongst the native ginkgo-
lides.[31] Inspection of the structure reveals three secondary
and one tertiary hydroxyl groups, which exhibit different re-
activities and can therefore be functionalized selectively. In
general, 10-OH is the most reactive for alkylation and ester-
ification.[35] However, acid-catalyzed esterification,[36] reac-
tion of GC (3) with alkyl and aryl sulfonyl halides in the
presence of pyridine[37,38] as well as silylation[39] takes place
at 7-OH; a selective silylation at 1-OH in the presence of
imidazole has also been described.[40]
In the next step, position 7 was derivatized by esterifica-
tion in the presence of pyridine. Thus, a series of GC-7-ben-
zoates 9, 10 and 11 were prepared in 79 92% yield
(Scheme 1). However, the use of H¸nig×s base (iPr2EtN) in-
stead of pyridine led to translactonization of ring E and for-
mation of esters 12 and 13 at position 6. This remarkable
difference in the reaction pattern is due to the higher basici-
ty of H¸nig×s base. The translactonized anion intermediate
is then stabilized by hydrogen bonding with 3-OH as report-
ed previously (Figure 3).[36] Thus, iso-GC-6-benzoates 12 and
13 were synthesized in 75 77% yield. Iso-GC-1,6-bisben-
zoate 14 was also prepared from 6 in 64% yield by increas-
ing the amount of benzoylation reagent and prolonging the
reaction time. Interestingly, the same reaction conditions ap-
plied to 13 provided only trace amounts of the correspond-
ing iso-GC-1,6-bisbenzoate. Acetylation of 6 and 7 with
acetic anhydride and H¸nig×s base led to bisacetates 15 and
16, respectively, in about 80% yield (Scheme 2).
The use of solid-phase synthesis (SPS) for the preparation
of ginkgolide derivatives appeared to be particularly attrac-
tive, as the presence of multiple hydroxyl groups provides
several options for connecting points. Hence various strat-
egies were investigated, including silicon,[41,42] sulfonyl,[43]
[44,45]
Wang,
and Rink amide[46] linkers. Interestingly, none of
the solid-phase methods studied was superior to the tradi-
tional solution-phase chemistry. The initial problem associat-
ed with solid-phase synthesis was the difficulty of attaching
ginkgolide C to the solid-phase due to a steric hindrance
and small reactivity of the ginkgolide hydroxyl groups. After
overcoming this obstacle with silyl linkers, bulkiness of the
silyl linker hampered further derivatization in some cases
whereas smaller linkers suffered from instability as evi-
denced by leaching. Selectivity of reactions on the solid-
phase was also significantly decreased; the products cleaved
from the resin were obtained in low yields with low purity.
The most promising approach appeared to be the attach-
ment of GC (3) via a 10-benzyloxy group to Wang resin; in
this case the final cleavage from the support took place sev-
Very few reports are available on the selective derivatiza-
tion of the 1-OH in GC. Although a selective silylation of 1-
[40]
OH has been carried out by Weinges the mechanism and
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Ginkgolides and Glycine Receptors
1507 1518
amine provided GC-1-ben-
zoates 17 and 18, respectively,
in 78 80% yield (Scheme 1).
The driving force for this rear-
rangement is the lower thermo-
dynamic stability of iso-GC
skeleton than the original GC.
Namely, the six-membered lac-
tone ring E in iso-GC adopts a
boat conformation. In addition,
the bulky tBu group in iso-GC
suffers from diaxial steric inter-
action with 6-H. The tertiary 3-
OH remained untouched as at-
tempts to derivatization under
more drastic esterification con-
ditions led to elimination prod-
ucts.
Scheme 1. Synthesis of ginkgolide C benzoates. a) K2CO3, DMF; b) BzCl (3 equiv), pyridine, CH2Cl2; c) Bz2O
(3 equiv), iPr2EtN, CH2Cl2; d) iPr2EtN, DMF, 1008C; e) Bz2O (6 equiv), iPr2EtN, CH2Cl2; PMB = p-methoxy-
benzyl.
All of the above reactions re-
quired protection of 10-OH. In
order to evaluate the effect of 10-OH substitution for GlyR
inhibition, deprotection was necessary. This was readily ac-
complished by oxidative removal of the p-methoxybenzyl
(PMB) group in derivatives 10, 13, and 18. The reaction was
facilitated by treatment with cerium(iv) ammonium nitrate
to obtain 19, 20, and 21 in 68 81% yield (Figure 4). Howev-
er, the milder oxidation reagent dichlorodicyano quinone
(DDQ) failed.
Figure 3. Stabilization of 6-O anion in translactonized GC as generated
by iPr2EtN.
Figure 4. Benzoates of ginkgolide C.
Scheme 2. Synthesis
of
10-alkoxy-iso-GC-1,6-bisacetates.
a) Ac2O
(10 equiv), iPr2EtN, CH2Cl2.
Introduction of carbamate moieties into the various hy-
droxyl groups of ginkgolides was investigated next. Carba-
mates are versatile sources of additional interactions such as
hydrogen bonding, hydrophobic interaction and steric repul-
sion. This could yield important information for SAR stud-
ies. Carbamates at 7-O were efficiently prepared from 10-
benzyloxy-GC (6) in two steps
scope of this reaction are not clear. We found that selective
derivatization of 1-OH can be achieved by acyl migration
from 6-O (iso-GC derivatives) via a six-membered cycle in-
termediate (Scheme 3). Thus heating of iso-GC-6-benzoates
12 and 13 at 1008C in DMF in the presence of a tertiary
(Scheme 4). Reaction with p-ni-
trophenylchloroformate
and
pyridine in CH2Cl2 gave 22 in
61% yield. Active carbonate 22
was further reacted with vari-
ous aliphatic amines in THF to
yield carbamates 23 26 in 81
92% yield (Table 1). Again, a
remarkable difference was ob-
served when H¸nig×s base was
used instead of pyridine
Scheme 3. Suggested mechanism of acyl migration from 6-O to 1-O with consequent translactonization of
ring E.
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K. Nakanishi, K. Str˘mgaard et al.
FULL PAPER
Scheme 4. Synthesis of 7-O carbamates from 10-alkoxy-GC. a) ClCOOC6H4NO2, pyridine, CH2Cl2; b) NHR1R2, THF; PMB = p-methoxybenzyl.
Table 2. Chemical yields and biological activities of 7-O and 1-O carba-
mates of ginkgolide C.
(Scheme 5). It is plausible that a highly reactive iso-GC
6-(p-nitrophenyl)carbonate is formed first, which reacts fur-
ther with 1-OH as in the case of the migration of benzoate
in 17. The product of this reaction, however, is cyclic car-
bonate 27 with a carbonyl bridging 1-O and 6-O (Scheme 5).
This active carbonate was unstable and hydrolyzed easily
even on silica gel to form 6. Treatment of 27 with various
aliphatic amines in THF provided facile opening of the car-
bonate cycle to form carbamates at 1-O with consequent
translactonization of ring E into the native form, 28 31. All
three reactions were finally performed in one pot to obtain
the desired 1-O derivatives in 50 78% overall yield from 6
after a single column chromatography (Table 1). Even bulky
amines such as tert-butyl amine reacted to completion in
both cases forming 24 and 29, ginkgolides with two tBu
groups. The corresponding sets of carbamates 33 36 (7-O)
(Scheme 4) and 38 41 (1-O) (Scheme 5) were also prepared
from 7. Removal of the PMB group from 33 36 and 38 41
afforded the non-aromatic ginkgolide carbamates 42 49
(Table 2) in 60 86% yield.
Compound R1
R2
Yield [%] Inhibition[b] [%]
42
43
44
45
46
47
48
49
H
H
H
H
CONHMe
CONHtBu
CONC4H8O 60
CONC5H10
H
H
H
H
69
80
NI
NI
44
34
76
71
NI
33
64
86
84
80
79
CONHMe
CONHtBu
CONC4H8O
CONC5H10
[a] (NH4)2Ce(NO3)6, MeCN/H2O/CHCl3. [b] Inhibition of 100mm glycine-
induced response by 100mm of test compound;%-inhibition was calculat-
ed as: (ResponseglycineÀResponsetest cmpd+glycine)/Responseglycine. Values are
means of three independent experiments performed in duplicate. NI=no
inhibition, i.e., inhibition below 20%. PMB=p-methoxybenzyl.
Biological activity: The ginkgolide derivatives were investi-
gated in their abilities to antagonize glycine-induced re-
sponses from homomeric a1 GlyRs. In brief, homomeric a1
GlyR was stably expressed in HEK293 cells and a fluores-
cence-based membrane-poten-
tial kit was used to detect re-
Table 1. Chemical yields and biological activities of C-7 and C-1 carbamates of 10-alkoxy-GC.
ceptor activity.[47] The de-
crease in glycine response was
measured by pre-incubation of
the test compound prior to ad-
dition of 100mm glycine. GC
(3) was used as the reference
compound. At a concentration
of 10 mm GC (3) the response
induced by glycine was inhib-
ited by 97%. Due to the rela-
tively low potency of all deriv-
atives, they were investigated
at concentrations of 100 mm
for determination of the % in-
hibition (Tables 1 4). Howev-
er, the fact that the parent
compound GC (3) was found
to be more potent than its de-
rivatives showed the signifi-
cant role played by the hy-
droxyl groups in GlyR interac-
tion. Thus, in the discussion
below it should be noted that
the relative differences be-
Compound
R
R1
R2
Yield [%]
Inhibition[a] [%]
23
24
25
26
28
29
30
31
33
34
35
36
38
39
40
41
Bn
Bn
Bn
Bn
Bn
Bn
Bn
Bn
PMB
PMB
PMB
PMB
PMB
PMB
PMB
PMB
H
H
H
H
CONHMe
CONHtBu
CONC4H8O
CONC5H10
H
H
H
H
CONHMe
CONHtBu
CONC4H8O
CONC5H10
H
H
H
H
88[b]
88[b]
92[b]
81[b]
64[c]
59[c]
78[c]
50[c]
74[d]
77[d]
90[d]
86[d]
67[e]
60[e]
75[e]
53[e]
NI
29
NI
NI
NI
42
NI
31
NI
39
NI
29
NI
33
NI
NI
CONHMe
CONHtBu
CONC4H8O
CONC5H10
H
H
H
H
CONHMe
CONHtBu
CONC4H8O
CONC5H10
[a] Inhibition of 100mm glycine-induced response by 100mm of test compound; % inhibition was calculated as:
(ResponseglycineÀResponsetest cmpd+glycine)/Responseglycine. Values are means of three independent experiments
performed in duplicate. [b] From 22. [c] From 6. [d] From 32. [e] From 7. NI=no inhibition, i.e., inhibition
below 20%. PMB=p-methoxybenzyl.
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Ginkgolides and Glycine Receptors
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Table 3. Biological activities of ginkgolide C derivatives.
Compound
R
R1
R2
Inhibition[a] [%]
6
9
17
7
Bn
Bn
Bn
PMB
2-picolyl
PMB
PMB
2-picolyl
H
H
H
Bz
H
H
H
Bz
H
H
Bz
H
Bz
H
H
H
Bz
H
Bz
Bz
H
59
45
60
52
75
35
NI
51
NI
NI
8
10
18
11
19
21
H
Scheme 5. Synthesis of 1-O carbamates from 10-alkoxy-GC; suggested
mechanism. a) ClCOOC6H4NO2, iPrEt2N, CH2Cl2; b) NHR1R2, CH2Cl2/
THF; PMB = p-methoxybenzyl.
[a] Inhibition of 100mm glycine-induced response by 100mm of
test compound; % inhibition was calculated as: (ResponseglycineÀRespon-
setest cmpd+glycine)/Responseglycine. Values are means of three independent ex-
periments performed in duplicate. NI=no inhibition, i.e., inhibition
below 20%. PMB=p-methoxybenzyl.
tween these derivatives are only minor since all compounds
are only weak antagonists of the GlyR.
Table 4. Biological activities of iso-ginkgolide C derivatives.
Ginkgolide derivatives with carbamates in position 1 or 7,
and a benzyl or PMB group in the 10-position were either
inactive or only moderately active at the concentrations
tested (Table 1). Interestingly, all derivatives with moderate
activity contained a tBu carbamate, and the presence of this
group, rather than the position seems to be of importance
for biological activity in this set of derivatives. For the corre-
sponding carbamates without the benzyl or PMB group it
appears that both the position and the nature of the sub-
stituent are of importance (Table 2): Compounds 46 and 47
show approximately 70% inhibition of the glycine respons-
es, whereas other derivatives are either inactive or only
moderately active. It is interesting to compare the activities
of 46 with those of 28 and 38, the only difference being the
benzyl or PMB substitution at 10-OH. This indicates that
10-OH substitution is detrimental for activity towards
GlyRs. Moreover, the activities of 46 and 47 compared with
those of 42 and 43 show that substitution at 1-OH is prefer-
red over 7-OH, while comparison with 48 and 49 indicates
that there may be a limitation to the size of the substituent
that is tolerated.
The benzylated or benzoylated derivatives of ginkgolide C
showed a certain degree of variation in activities (Table 3).
The most potent derivatives were those with only one
benzyl substituent at 10-OH, such as compounds 6, 7 and 8.
Particularly compound 8 with a 2-picolyl substituent exhibit-
ed 75% inhibition. Addition of benzoyl groups does not im-
prove activity, while the presence of only one benzoyl
group, such as 19 and 21 leads to a complete loss in activity.
Finally, a range of iso-ginkgolide derivatives was investigat-
ed, with some showing reasonable potencies (Table 4). Par-
ticularly compound 12, with a 90% inhibition in glycine re-
sponses is the most potent of the 40 derivatives. On the
other hand, it is still considerably less potent than GC (3), a
30 mm concentration of 12 giving only a 39% inhibition.
compound
R
R1
R2
Inhibition[a] [%]
12
15
16
14
13
20
Bn
Bn
PMB
Bn
PMB
H
H
Bz
Ac
Ac
Bz
Bz
Bz
90
21
36
42
49
63
Ac
Ac
Bz
H
H
[a] Inhibition of 100mm glycine-induced response by 100mm of
test compound;%-inhibition was calculated as: (ResponseglycineÀRespon-
setest cmpd+glycine)/Responseglycine. Values are means of three independent ex-
periments performed in duplicate.
Conclusion
We have shown that ginkgolide C in solution can be selec-
tively transformed into various derivatives via rearrange-
ment and migration. Particularly, a selective method for sub-
stitution at 1-OH has been found. Since hydroxyl groups
that are unchanged in the product, for example, 3-OH and
7-OH, participate during the reaction process, their protec-
tion would presumably hamper the entire reaction. The role
of 7-OH in the substitution of 1-OH described here is cru-
cial. We have also investigated a solid-phase approach for
preparation of a ginkgolide library. Ginkgolide C was suc-
cessfully attached to solid-phase but the derivatization reac-
tions on the resin were much less efficient as compared to
solution-phase reactions. Particularly, selectivity was greatly
diminished.
The synthesized ginkgolide derivatives were investigated
as GlyR antagonists using a high-throughput screening
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K. Nakanishi, K. Str˘mgaard et al.
FULL PAPER
12.4 Hz, 1H, 8-H), 1.30 (d, J=7.0 Hz, 3H, 16-CH3), 1.23 (s, 9H, tBu);
13C NMR (100 MHz, CDCl3): d=175.83, 171.03, 170.90, 160.56, 130.65,
126.36, 114.73, 110.13, 98.49, 90.70, 83.47, 79.33, 75.59, 75.31, 73.79, 67.08,
64.03, 55.31, 50.38, 41.65, 32.19, 29.08, 7.23; HRMS (FAB): m/z: calcd for
C28H32O12: 560.1894; found: 560.1866 [M]+.
assay. In general, the ginkgolide derivatives prepared were
less potent than the parent compound (3), and in many
cases the derivatives were totally devoid of activity. These
results indicate that substitutions of the hydroxyl groups in
ginkgolides are not beneficial for antagonistic activity at
GlyR, and clearly other means of improving the activity of
the parent compounds will be required. In addition, these
results show that the structure activity relationships differ
significantly from those observed with PAFR, as best exem-
plified by the iso-ginkgolide derivatives. When tested against
PAFR, iso-GC acetates were devoid of activity;[36] however,
in the present studies, although much less potent than the
parent compound (3), the iso-ginkgolide derivative 12 was
the most potent of the compounds tested.
Previous studies have indicated that ginkgolides might an-
tagonize GlyRs by binding to an intra-ion channel site,[31]
thus acting as a plug in the ion channel of the GlyR. More-
over, it has been suggested that the conformation of the
ginkgolide is very important for antagonistic activity.[32] This
study suggests that the hydroxyl groups are critical for the
GlyR inhibition.
10-(2-Pyridinyl-methoxy)-GC (8): A mixture of 2-picolylchloride hydro-
chloride (401.4 mg, 2.45 mmol, 6 equiv) and EtOAc was washed with sat.
aq. NaHCO3 (2î), brine. The organic phase was subsequently dried with
MgSO4. After filtration and removal of EtOAc, free 2-picolyl chloride
was added to a solution of GC (3) (179.6 mg, 0.408 mmol, 1 equiv) in
DMF (2.04 mL) and powdered K2CO3 (338 mg, 2.45 mmol, 6 equiv) was
added. The mixture was briefly heated to about 608C and then stirred at
room temperature for 15 h. The solution was concentrated under reduced
pressure, an aq. phosphate buffer (pH 2 3, 10 mL) was added and result-
ing solution was extracted with EtOAc (3î) and dried with MgSO4. The
crude product was purified by flash chromatography (50 100% EtOAc/
hexanes) to obtain 8 as a white powder (211.2 mg, 97%). 1H NMR
(400 MHz, CDCl3): d=8.54 (d, J=4.9 Hz, 1HAR), 8.20 (d, J=4.1 Hz, 1H,
1-OH), 7.79 7.71 (m, 1HAR), 7.35 7.28 (m, 1HAR), 7.19 7.11 (m, 1HAR),
6.00 (s, 1H, 12-H), 5.67 (d, J=13.0 Hz, 1H, benzylic), 5.43 (d, J=4.3 Hz,
1H, 6-H), 4.96 (s, 1H, 10-H), 4.82 (d, J=13.0 Hz, 1H, benzylic), 4.66 (d,
J=7.6 Hz, 1H, 2-H), 4.47 4.38 (m, 1H, 1-H), 4.27 4.17 (m, 1H, 7-H),
3.10 (s, 1H, 3-OH), 3.08 (q, J=7.0 Hz, 1H, 14-H), 2.32 (d, J=11.3 Hz,
1H, 7-OH), 1.73 (d, J=12.4 Hz, 1H, 8-H), 1.30 (d, J=7.0 Hz, 3H, 16-
CH3), 1.18 (s, 9H, tBu); 13C NMR (100 MHz, CDCl3): d=175.79, 171.45,
170.96, 154.52, 148.74, 137.41, 123.29, 120.37, 109.99, 98.74, 92.61, 83.06,
80.14, 75.36, 74.89, 73.81, 70.67, 67.62, 64.70, 50.55, 41.74, 32.27, 29.12,
7.33; HRMS (FAB): m/z: calcd for C26H30O11N: 532.1819; found:
532.1844 [M+H]+.
Experimental Section
10-Benzyloxy-GC-7-benzoate (9): Benzoyl chloride (25 mL, 0.216 mmol,
5 equiv) was added to a solution of 6 (22.9 mg, 0.043 mmol) in CH2Cl2
(0.9 mL) and pyridine (0.15 mL, 1.85 mmol, 43 equiv). The mixture was
stirred for 7 h and then quenched with aq. HCl (1 mL, 1m), extracted
with EtOAc (3î) and dried with MgSO4. The crude product was purified
by flash chromatography (30 50% EtOAc/hexanes) to obtain 9 as a
Materials and methods: All reactions were performed under argon at
ambient temperature in dry solvents and yields refer to isolated products,
unless otherwise stated. Ginkgolide C (3) originated from early structural
13]
studies,[9 and was recrystallized from ethanol/water and dried in desic-
1
cator. All other reagents were purchased and used as received. Polystyr-
ene resin, Wang resin and bromopolystyrene resin were obtained from
Advanced ChemTech, DES resin and sulfonyl chloride resin were ob-
tained from Aldrich, Tentagel resin was purchased from Rapp-Polymere
GmbH, T¸bingen (Germany). Reactions were monitored by analytical
TLC with silica gel 60 F254 and spots were visualized by heating and UV
light (254 nm). Flash chromatography was performed using silica gel
(230 400 mesh).
1H NMR and 13C NMR spectra were recorded with Bruker (300, 400 or
500 MHz) spectrometers. The chemical shifts are expressed in ppm (d)
downfield from tetramethylsilane (in CDCl3) or calibrated according to
residual solvent peak as an internal standard (MeOD, d 3.30). Assign-
ment of peaks was achieved using 2D methods (COSY), by comparison
with published data where available and comparison with 1H NMR spec-
tra of parent ginkgolides. In certain cases, HSQC was used instead of
13C NMR. High-resolution mass spectra (HRMS) were measured on
JEOL JMS-HX110/100A HF mass spectrometer under FAB conditions
with NBA as the matrix. In general, all ginkgolide derivatives decom-
posed above 2508C.
white powder (21.6 mg, 79%). H NMR (400 MHz, CDCl3): d=8.12 8.05
(m, 2HAR), 7.68 7.58 (m, 1HAR), 7.53 7.40 (m, 7HAR), 6.08 (s, 1H, 12-H),
5.50 (dd, J=12.9, 4.3 Hz, 1H, 7-H), 5.48 (d, J=9.4 Hz, 1H, benzylic),
5.41 (d, J=4.3 Hz, 1H, 6-H), 5.02 (s, 1H, 10-H), 4.76 (d, J=9.4 Hz, 1H,
benzylic), 4.51 (d, J=7.9 Hz, 1H, 2-H), 4.26 (dd, J=7.9, 3.2 Hz, 1H, 1-
H), 3.07 (q, J=7.0 Hz, 1H, 14-H), 2.86 (d, J=3.2 Hz, 1H, 1-OH), 2.9 2.7
(brs, 1H, 3-OH), 2.25 (d, J=12.9 Hz, 1H, 8-H), 1.31 (d, J=7.0 Hz, 3H,
16-CH3), 1.20 (s, 9H, tBu); 13C NMR (100 MHz, CDCl3): d=175.13,
170.97, 170.50, 164.84, 134.12, 133.95, 130.06, 129.85, 129.57, 128.80,
128.74, 128.60, 109.86, 98.34, 90.53, 83.41, 76.88, 75.39, 74.15, 74.01, 73.93,
67.83, 64.03, 48.60, 41.57, 32.13, 29.36, 7.26; HRMS (FAB): m/z: calcd for
C34H35O12: 635.2129; found: 635.2156 [M+H]+.
10-(4-Methoxy-benzyloxy)-GC-7-benzoate (10): The compound was syn-
thesized from 7 according to the procedure for 9. Product was obtained
as a white solid (92%). 1H NMR (300 MHz, CDCl3): d=8.13 8.03 (m,
2HAR), 7.69 7.58 (m, 1HAR), 7.54 7.44 (m, 2HAR), 7.44 7.34 (m, 2HAR),
7.03 6.94 (m, 2HAR), 6.07 (s, 1H, 12-H), 5.48 (dd, J=12.8, 4.3 Hz, 1H, 7-
H), 5.40 (d, J=9.3 Hz, 1H, benzylic), 5.40 (d, J=4.3 Hz, 1H, 6-H), 4.99
(s, 1H, 10-H), 4.70 (d, J=9.3 Hz, 1H, benzylic), 4.50 (d, J=7.9 Hz, 1H,
2-H), 4.25 (dd, J=7.9, 3.4 Hz, 1H, 1-H), 3.84 (s, 3H, OMe), 3.06 (q, J=
7.0 Hz, 1H, 14-H), 2.92 (d, J=3.4 Hz, 1H, 1-OH), 2.90 (s, 1H, 3-OH),
2.24 (d, J=12.8 Hz, 1H, 8-H), 1.31 (d, J=7.0 Hz, 3H, 16-CH3), 1.20 (s,
9H, tBu); 13C NMR (75 MHz, CDCl3): d=175.28, 171.00, 170.65, 164.84,
160.61, 133.94, 130.57, 130.05, 128.73, 128.59, 126.18, 114.82, 109.87, 98.31,
90.54, 83.41, 76.84, 75.05, 73.97, 73.94, 73.70, 67.81, 64.01, 55.33, 48.57,
10-Benzyloxy-GC (6): Synthesis and analytical data as previously descri-
bed.[38]
10-(4-Methoxy-benzyloxy)-GC (7): Powdered K2CO3 (315 mg, 2.28 mmol,
5 equiv) and 4-methoxybenzyl chloride (620 mL, 4.56 mmol, 10 equiv)
were added to a solution of GC (3) (201 mg, 0.456 mmol) in DMF
(2.28 mL). The mixture was stirred at 608C for 3 h and then stirred at
room temperature for 5 h. The solution was concentrated under reduced
pressure, an aq. phosphate buffer (pH 2 3, 10 mL) was added and the re-
sulting solution was extracted with EtOAc (3î) and dried with MgSO4.
The crude product was purified by flash chromatography (40 100%
EtOAc/hexanes) to obtain 7 as a white powder (240 mg, 94%). 1H NMR
(300 MHz, CDCl3): d=7.35 7.27 (m, 2HAR), 6.99 6.89 (m, 2HAR), 5.98
(s, 1H, 12-H), 5.41 (d, J=9.2 Hz, 1H, benzylic), 5.12 (d, J=4.4 Hz, 1H,
6-H), 4.92 (s, 1H, 10-H), 4.57 (d, J=9.2 Hz, 1H, benzylic), 4.52 (d, J=
7.9 Hz, 1H, 2-H), 4.21 (dd, J=3.4, 7.9 Hz, 1H, 1-H), 4.13 (m, 1H, 7-H),
3.83 (s, 3H, OMe), 3.05 (q, J=7.1 Hz, 1H, 14-H), 2.88 (d, J=3.4 Hz, 1H,
1-OH), 2.75 (s, 1H, 3-OH), 2.12 (d, J=11.5 Hz, 1H, 7-OH), 1.69 (d, J=
41.61, 32.10, 29.34, 7.28; HRMS (FAB): m/z: calcd for C35H36O13
:
664.2156; found: 664.2129 [M]+.
10-(2-Pyridinyl-methoxy)-GC-7-benzoate (11): The compound was syn-
thesized from 8 according to the procedure for 9. Product was obtained
as a white solid (85%). 1H NMR (400 MHz, CDCl3): d=8.58 (d, J=
5.0 Hz, 1H, 6-py), 8.42 (brs, 1H, 1-OH), 8.08 8.00 (m, 2HAR), 7.79 7.71
(m, 1H, 4-py), 7.65 7.56 (m, 1HAR), 7.51 7.42 (m, 2HAR), 7.35 7.28 (m,
1H, 5-py), 7.15 (d, J=7.9 Hz, 1H, 3-py), 6.08 (s, 1H, 12-H), 5.75 (d, J=
4.4 Hz, 1H, 6-H), 5.68 (d, J=13.1 Hz, 1H, benzylic), 5.48 (dd, J=12.8,
4.4 Hz, 1H, 7-H), 5.03 (s, 1H, 10-H), 4.89 (d, J=13.1 Hz, 1H, benzylic),
4.64 (d, J=7.5 Hz, 1H, 2-H), 4.48 (brd, J=7.5 Hz, 1H, 1-H), 3.09 (q, J=
1512
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 1507 1518

Ginkgolides and Glycine Receptors
1507 1518
7.0 Hz, 1H, 14-H), 2.88 (brs, 1H, 3-OH), 2.28 (d, J=12.8 Hz, 1H, 8-H),
1.31 (d, J=7.0 Hz, 3H, 16-CH3), 1.18 (s, 9H, tBu); 13C NMR (100 MHz,
CDCl3): d=175.63, 171.53, 170.71, 164.87, 154.47, 148.85, 137.37, 133.78,
130.00, 128.84, 128.67, 123.28, 120.22, 109.94, 98.68, 92.62, 83.04, 77.53,
74.93, 74.35, 73.84, 70.65, 68.43, 64.61, 48.89, 41.76, 32.24, 29.39, 7.34;
HRMS (FAB): m/z: calcd for C33H34O12N: 636.2081; found: 636.2058
[M+H]+.
J=7.5 Hz, 1H, 14-H), 3.30 (s, 1H, 3-OH), 2.20 (s, 1H, 8-H), 2.12 (s, 3H,
Ac), 1.31 (d, J=7.5 Hz, 3H, 16-CH3), 1.30 (s, 3H, Ac), 1.19 (s, 9H, tBu);
13C NMR (75 MHz, CDCl3): d=175.87, 170.07, 168.74, 167.87, 166.51,
135.22, 128.93, 128.76 (2 C), 108.60, 97.31, 92.04, 84.47, 78.99, 74.98,
74.25, 73.29, 70.13, 67.20, 63.67, 61.55, 41.21, 33.63, 29.26, 20.59, 19.52,
9.56; HRMS (FAB): m/z: calcd for C31H35O13: 615.2078; found: 615.2083
[M+H]+.
10-Benzyloxy-isoGC-6-benzoate (12): Benzoic anhydride (23 mg,
0.102 mmol, 3 equiv) was added to a solution of 6 (18.0 mg, 0.034 mmol)
in CH2Cl2 (0.87 mL) and iPr2EtN (0.145 mL, 0.829 mmol, 24 equiv). The
mixture was stirred for 11 h and then quenched with phosphate buffer
(pH ~2 3, 1 mL) washed with brine. The organic phase was subsequently
dried with MgSO4. The crude product was purified by flash chromatogra-
phy (30 50% EtOAc/hexanes) to obtain 12 as a white powder (16.6 mg,
77%). 1H NMR (400 MHz, CDCl3): d=8.15 8.09 (m, 2HAR), 7.66 7.56
(m, 1HAR), 7.52 7.38 (m, 7HAR), 5.75 (s, 1H, 12-H), 5.48 (d, J=9.5 Hz,
1H, benzylic), 5.44 (d, J=4.0 Hz, 1H, 6-H), 5.17 (s, 1H, 10-H), 5.06 (d,
J=3.9 Hz, 1H, 7-H), 4.91 (d, J=7.7 Hz, 1H, 2-H), 4.83 (d, J=9.5 Hz,
1H, benzylic), 4.28 (dd, J=7.6, 2.3 Hz, 1H, 1-H), 3.83 (s, 1H, 3-OH),
3.22 (q, J=7.1 Hz, 1H, 14-H), 3.22 (d, J=2.4 Hz, 1H, 1-OH), 2.30 (s,
1H, 8-H), 1.35 (d, J=7.1 Hz, 3H, 16-CH3), 1.25 (s, 9H, tBu); 13C NMR
(100 MHz, CDCl3): d=176.38, 170.70, 166.56, 165.09, 134.18, 133.65,
130.19, 129.90, 129.46, 129.23, 128.80, 127.82, 110.02, 95.53, 91.96, 84.07,
78.81, 75.21, 74.29, 73.11, 69.90, 67.73, 62.86, 61.78, 41.47, 33.74, 29.71,
6.99; HRMS (FAB): m/z: calcd for C34H35O12: 635.2129; found: 635.2097
[M+H]+.
10-(4-Methoxy-benzyloxy)-isoGC-1,6-bisacetate (16): The compound was
synthesized from 7 according to the procedure for 15. Product was ob-
tained as a white solid (79%). H NMR (400 MHz, CDCl3): d=7.31 7.24
1
(m, 2HAR), 6.93 6.86 (m, 2HAR), 5.64 (d, J=3.8 Hz, 1H, 1-H), 5.63 (s,
1H, 12-H), 5.45 (d, J=4.1 Hz, 1H, 6-H), 5.18 (d, J=10.4 Hz, 1H, benzyl-
ic), 5.00 (s, 1H, 10-H), 4.82 (d, J=4.1 Hz, 1H, 7-H), 4.69 (d, J=10.4 Hz,
1H, benzylic), 4.50 (d, J=3.8 Hz, 1H, 2-H), 3.81 (s, 3H, OMe), 3.34 (s,
1H, 3-OH), 3.30 (q, J=7.5 Hz, 1H, 14-H), 2.20 (s, 1H, 8-H), 2.12 (s, 3H,
Ac), 1.39 (s, 3H, Ac), 1.30 (d, J=7.5 Hz, 3H, 16-CH3), 1.17 (s, 9H, tBu);
13C NMR (100 MHz, CDCl3): d=175.34, 169.65, 168.21, 167.33, 165.97,
159.46, 130.36, 126.79, 113.65, 108.29, 96.83, 91.75, 84.15, 78.70, 74.18,
73.84, 72.62, 69.90, 66.87, 63.41, 61.28, 55.17, 41.08, 33.52, 29.27, 20.53,
19.62, 9.40; HSQC correlation spectra measured; HRMS (FAB): m/z:
calcd for C32H36O14: 644.2105; found: 644.2082 [M]+.
10-Benzyloxy-GC-1-benzoate (17): iPr2EtN (50 mL, 0.29 mmol, 12 equiv)
was added to a solution of 12 (15.6 mg, 0.025 mmol) in DMF (0.40 mL)
and mixture was stirred for 3 h at 1008C. Solvent was removed under re-
duced pressure, a residue was treated with phosphate buffer (pH 2 3,
1 mL), then extracted with EtOAc (3î) and combined organic layers
were dried with MgSO4. The crude product was purified by flash chroma-
10-(4-Methoxy-benzyloxy)-isoGC-6-benzoate (13): The compound was
synthesized from 7 according to the procedure for 12. Product was ob-
tography (30 50% EtOAc/hexanes) to obtain 17 as
a white solid
1
(12.2 mg, 78%). 1H NMR (400 MHz, CDCl3): d=7.64 7.59 (m, 2HAR),
7.51 7.45 (m, 1HAR), 7.31 7.25 (m, 2HAR), 6.98 6.91 (m, 2HAR), 6.88
6.83 (m, 3HAR), 6.03 (s, 1H, 12-H), 5.89 (d, J=6.1 Hz, 1H, 1-H), 5.46 (d,
J=4.4 Hz, 1H, 6-H), 5.17 (d, J=11.0 Hz, 1H, benzylic), 4.85 (s, 1H, 10-
H), 4.70 (d, J=6.1 Hz, 1H, 2-H), 4.56 (d, J=10.9 Hz, 1H, benzylic),
4.42 4.33 (m, 1H, 7-H), 3.28 (q, J=7.2 Hz, 1H, 14-H), 3.4 2.9 (brs, 1H,
3-OH), 2.65 2.3 (brs, 1H, 7-OH), 1.76 (d, J=12.3 Hz, 1H, 8-H), 1.33 (d,
J=7.2 Hz, 3H, 16-CH3), 1.15 (s, 9H, tBu); 13C NMR (100 MHz, CDCl3):
d=174.91, 170.70, 170.25, 163.47, 134.66, 133.23, 129.56, 128.70, 128.34,
128.24, 128.11, 128.02, 109.34, 99.62, 92.14, 84.27, 80.32, 75.64, 75.25,
74.30, 73.55, 66.47, 65.09, 50.57, 41.20, 32.34, 29.13, 7.94; HRMS (FAB):
m/z: calcd for C34H35O12: 635.2129; found: 635.2148 [M+H]+.
tained as a white solid (75%). H NMR (400 MHz, CDCl3): d=8.15 8.08
(m, 2HAR), 7.62 7.55 (m, 1HAR), 7.48 7.39 (m, 2HAR), 7.38 7.30 (m,
2HAR), 6.96 6.88 (m, 2HAR), 5.74 (s, 1H, 12-H), 5.42 (d, J=4.0 Hz, 1H,
6-H), 5.40 (d, J=9.4 Hz, 1H, benzylic), 5.16 (s, 1H, 10-H), 5.06 (d, J=
4.0 Hz, 1H, 7-H), 4.91 (d, J=7.7 Hz, 1H, 2-H), 4.76 (d, J=9.4 Hz, 1H,
benzylic), 4.27 (dd, J=7.7, 2.6 Hz, 1H, 1-H), 3.84 (s, 1H, 3-OH), 3.79 (s,
3H, OMe), 3.30 (d, J=2.7 Hz, 1H, 1-OH), 3.22 (q, J=7.1 Hz, 1H, 14-H),
2.30 (s, 1H, 8-H), 1.35 (d, J=7.1 Hz, 3H, 16-CH3), 1.25 (s, 9H, tBu);
13C NMR (75 MHz, CDCl3): d=176.40, 170.84, 166.61, 165.11, 160.71,
134.17, 130.98, 130.23, 128.80, 127.88, 125.78, 114.76, 110.06, 95.51, 91.98,
84.11, 78.86, 74.94, 73.86, 73.12, 69.96, 67.76, 62.91, 61.79, 55.31, 41.49,
33.76, 29.39, 6.99; HRMS (FAB): m/z: calcd for C35H36O13: 664.2156;
found: 664.2165 [M]+.
10-(4-Methoxy-benzyloxy)-GC-1-benzoate (18): The compound was syn-
thesized from 13 according to the procedure for 17. Product was obtained
as a white solid (80%). 1H NMR (400 MHz, CDCl3): d=7.64 7.58 (m,
2HAR), 7.52 7.45 (m, 1HAR), 7.32 7.25 (m, 2HAR), 6.91 6.85 (m, 2HAR),
6.39 6.33 (m, 2HAR), 6.02 (s, 1H, 12-H), 5.84 (d, J=6.2 Hz, 1H, 1-H),
5.44 (d, J=4.4 Hz, 1H, 6-H), 5.10 (d, J=10.5 Hz, 1H, benzylic), 4.83 (s,
1H, 10-H), 4.68 (d, J=6.2 Hz, 1H, 2-H), 4.47 (d, J=10.5 Hz, 1H, benzyl-
ic), 4.42 4.33 (m, 1H, 7-H), 3.60 (s, 3H, OMe), 3.28 (q, J=7.1 Hz, 1H,
14-H), 3.09 (s, 1H, 3-OH), 2.37 (d, J=12.0 Hz, 1H, 7-OH), 1.74 (d, J=
12.3 Hz, 1H, 8-H), 1.33 (d, J=7.1 Hz, 3H, 16-CH3), 1.18 (s, 9H, tBu);
13C NMR (125 MHz, CDCl3): d=174.72, 170.67, 170.31, 163.43, 159.24,
133.01, 129.88, 129.57, 128.71, 128.18, 126.84, 113.44, 109.33, 99.43, 92.11,
84.25, 80.32, 75.62, 74.99, 74.24, 73.31, 66.39, 65.09, 54.81, 50.65, 41.17,
32.34, 29.17, 7.85; HRMS (FAB): m/z: calcd for C35H36O13: 664.2156;
found: 664.2170 [M]+.
10-Benzyloxy-isoGC-1,6-bisbenzoate (14): Benzoic anhydride (19.9 mg,
0.090 mmol, 6 equiv) was added to a solution of 6 (9.3 mg, 0.015 mmol)
in CH2Cl2 (0.38 mL) and iPr2EtN (63 mL, 0.36 mmol, 24 equiv). The mix-
ture was stirred for 20 h and then quenched with aq. HCl (1 mL, 1m),
washed with brine. The organic phase was subsequently dried with
MgSO4. The crude product was purified by flash chromatography (30
50% EtOAc/1% AcOH/hexanes) to obtain 14 as
a white powder
(7.1 mg, 64%). 1H NMR (400 MHz, CDCl3): d=8.25 8.18 (m, 2HAR),
7.66 7.58 (m, 3HAR), 7.52 7.37 (m, 3HAR), 7.21 7.13 (m, 2HAR), 7.11
7.03 (m, 2HAR), 7.02 6.95 (m, 3HAR), 6.02 (d, J=5.1 Hz, 1H, 1-H), 5.79
(d, J=4.0 Hz, 1H, 6-H), 5.69 (s, 1H, 12-H), 5.03 (d, J=4.0 Hz, 1H, 7-H),
5.01 (s, 1H, 10-H), 4.88 (d, J=5.1 Hz, 1H, 2-H), 4.86 (s, 2H, benzylic),
3.66 (s, 1H, 3-OH), 3.41 (q, J=7.3 Hz, 1H, 14-H), 2.25 (s, 1H, 8-H), 1.39
(d, J=7.3 Hz, 3H, 16-CH3), 1.08 (s, 9H, tBu); 13C NMR (75 MHz,
CDCl3): d=175.91, 170.05, 166.74, 165.61, 163.78, 134.37, 133.92, 133.08,
130.21, 129.58, 129.22, 128.98, 128.91, 128.62, 128.29, 128.25, 127.96,
109.00, 96.69, 92.51, 84.72, 79.05, 74.05, 73.78, 72.94, 71.02, 67.11, 64.01,
GC-7-Benzoate (19): An aq. solution of (NH4)2Ce(NO3)6 (14.7 mL,
24 mmol, 2 equiv, 1.63m) was added to
a solution of 10 (8.0 mg,
12.0 mmol) in acetonitrile (150 mL) and CHCl3 (49 mL). The mixture was
stirred for 14 h, volatiles were removed under reduced pressure and resi-
due was purified by flash chromatography (30 100% EtOAc/1% AcOH/
61.61, 41.42, 33.73, 29.21, 8.60; HRMS (FAB): m/z: calcd for C41H39O13
:
739.2391; found: 739.2381 [M+H]+.
10-Benzyloxy-isoGC-1,6-bisacetate (15): Acetic anhydride (15 mL,
0.16 mmol, 10 equiv) was added to a solution of 6 (8.5 mg, 0.016 mmol)
in CH2Cl2 (0.15 mL) and iPr2EtN (28 mL, 0.16 mmol, 10 equiv). Mixture
was stirred for 12 h and then quenched with aq. HCl (1 mL, 1m), extract-
ed with EtOAc (3î). The organic phase was subsequently dried with
MgSO4. The crude product was purified by flash chromatography (40
50% EtOAc/hexanes) to obtain 15 as a white powder (8.0 mg, 81%).
1H NMR (300 MHz, CDCl3): d=7.43 7.38 (m, 5HAR), 5.66 (d, J=3.7 Hz,
1H, 1-H), 5.63 (s, 1H, 12-H), 5.51 (d, J=4.1 Hz, 1H, 6-H), 5.30 (d, J=
10.6 Hz, 1H, benzylic), 5.01 (s, 1H, 10-H), 4.83 (d, J=4.1 Hz, 1H, 7-H),
4.72 (d, J=10.6 Hz, 1H, benzylic), 4.48 (d, J=3.7 Hz, 1H, 2-H), 3.31 (q,
hexanes) to obtain 19 as
a
white powder (4.4 mg, 68%). 1H NMR
(400 MHz, CD3OD): d=8.11 8.05 (m, 2HAR), 7.70 7.62 (m, 1HAR), 7.57
7.49 (m, 2HAR), 6.20 (s, 1H, 12-H), 5.54 5.46 (m, 2H, 6-H and 7-H), 5.19
(s, 1H, 10-H), 4.57 (d, J=7.6 Hz, 1H, 2-H), 4.22 (d, J=7.6 Hz, 1H, 1-H),
3.02 (q, J=7.1 Hz, 1H, 14-H), 2.29 2.22 (m, 1H, 8-H), 1.23 (d, J=7.1 Hz,
3H, 16-CH3), 1.18 (s, 9H, tBu); HSQC correlation spectra measured;
HRMS (FAB): m/z: calcd for C27H28O12Na: 567.1478; found: 567.1472
[M+Na]+.
IsoGC-6-benzoate (20): An aq. solution of (NH4)2Ce(NO3)6 (6.2 mL,
10 mmol, 2 equiv, 1.63m) was added to a solution of 13 (3.3 mg, 5.0 mmol)
1513
Chem. Eur. J. 2004, 10, 1507 1518
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

K. Nakanishi, K. Str˘mgaard et al.
FULL PAPER
in acetonitrile (63 mL) and CHCl3 (20 mL). The mixture was stirred for
3 h, volatiles were removed under reduced pressure and residue was puri-
fied by flash chromatography (30 70% EtOAc/1% AcOH/hexanes) to
3.4 Hz, 1H, 1-H), 3.04 (q, J=7.0 Hz, 1H, 14-H), 2.81 (d, J=3.4 Hz, 1H,
1-OH), 2.69 (s, 1H, 3-OH), 1.98 (d, J=12.8 Hz, 1H, 8-H), 1.35 (s, 9H,
tBu), 1.30 (d, J=7.0 Hz, 3H, 16-CH3), 1.15 (s, 9H, tBu); 13C NMR
(125 MHz, CDCl3): d=175.08, 171.09, 170.62, 152.11, 134.16, 129.73,
129.50, 128.85, 109.97, 98.34, 90.56, 83.43, 77.56, 75.39, 74.10, 74.07, 73.38,
67.65, 63.95, 50.93, 48.65, 41.53, 32.10, 29.33, 28.82, 7.21; HSQC correla-
tion spectra measured; HRMS (FAB): m/z: calcd for C32H39O12NNa:
652.2370; found: 652.2368 [M+Na]+.
1
obtain 20 as a white powder (2.2 mg, 81%). H NMR (400 MHz, CDCl3):
d=8.18 8.11 (m, 2HAR), 7.63 7.55 (m, 1HAR), 7.48 7.40 (m, 2HAR), 5.75
(s, 1H, 12-H), 5.64 (d, J=3.9 Hz, 1H, 6-H), 5.30 (s, 1H, 10-H), 5.06 (d,
J=3.9 Hz, 1H, 7-H), 5.00 (d, J=7.7 Hz, 1H, 2-H), 4.26 (d, J=7.7 Hz,
1H, 1-H), 3.78 (s, 1H, 3-OH), 3.40 (q, J=7.1 Hz, 1H, 14-H), 2.29 (s, 1H,
8-H), 1.37 (d, J=7.1 Hz, 3H, 16-CH3), 1.26 (s, 9H, tBu); HSQC correla-
7-(Morpholine-4-carbonyloxy)-10-benzyloxy-GC (25): Morpholine (2 mL,
23 mmol, 3 equiv) was added to a solution of 22 (5.2 mg, 7.5 mmol) in
THF (0.15 mL). The mixture was stirred for 25 min and then quenched
with aq. HCl (1 mL, 1m), extracted with EtOAc (3î) and dried with
MgSO4. The crude product was purified by flash chromatography (40
50% EtOAc/hexanes) to obtain 25 as a white solid (6.0 mg, 92%).
1H NMR (400 MHz, CDCl3): d=7.49 7.38 (m, 5HAR), 6.03 (s, 1H, 12-H),
5.44 (d, J=9.4 Hz, 1H, benzylic), 5.32 5.23 (m, 2H, 6-H and 7-H), 4.97
(s, 1H, 10-H), 4.74 (d, J=9.4 Hz, 1H, benzylic), 4.48 (d, J=7.8 Hz, 1H,
2-H), 4.22 (dd, J=7.8, 3.5 Hz, 1H, 1-H), 3.77 3.33 (m, 8H, morph.), 3.04
(q, J=7.0 Hz, 1H, 14-H), 2.93 (s, 1H, 3-OH), 2.80 (d, J=3.5 Hz, 1H, 1-
OH), 2.09 2.00 (m, 1H, 8-H), 1.30 (d, J=7.0 Hz, 3H, 16-CH3), 1.17 (s,
9H, tBu); 13C NMR (100 MHz, CDCl3): d=175.16, 171.02, 170.53,
152.99,134.10, 129.78, 129.51, 128.80, 109.88, 98.39, 90.58, 83.40, 77.14,
75.30, 74.68, 74.06, 73.97, 67.56, 66.59 (morph.), 66.48 (morph.), 63.94,
48.62, 44.48 (morph.), 44.21 (morph.), 41.57, 32.13, 29.31, 7.27; HRMS
(FAB): m/z: calcd for C32H38O13N: 644.2343; found: 644.2333 [M+H]+.
tion spectra measured; HRMS (FAB): m/z: calcd for C27H29O12
:
545.1659; found: 545.1666 [M+H]+.
GC-1-Benzoate (21): An aq. solution of (NH4)2Ce(NO3)6 (9.8 mL,
16 mmol, 2 equiv, 1.63m) was added to a solution of 18 (5.3 mg, 8.0 mmol)
in acetonitrile (100 mL) and CHCl3 (32 mL). The mixture was stirred for
1.5 h, aq. solution of (NH4)2Ce(NO3)6 (4.9 mL, 8 mmol, 1 equiv, 1.63m)
was added and mixture was further stirred for 12 h. Volatiles were re-
moved under reduced pressure and residue was purified by flash chroma-
tography (40 70% EtOAc/hexanes) to obtain 21 as a white powder
(2.6 mg, 60%). 1H NMR (300 MHz, CDCl3): d=7.98 7.90 (m, 2HAR),
7.67 7.58 (m, 1HAR), 7.51 7.41 (m, 2HAR), 6.05 (s, 1H, 12-H), 5.77 (d,
J=6.8 Hz, 1H, 1-H), 5.47 (d, J=4.3 Hz, 1H, 6-H), 5.09 (d, J=1.9 Hz,
1H, 10-H), 4.77 (d, J=6.8 Hz, 1H, 2-H), 4.40 4.28 (m, 1H, 7-H), 3.56 (d,
J=1.9 Hz, 1H, 10-OH), 3.22 (q, J=7.1 Hz, 1H, 14-H), 2.86 (s, 1H, 3-
OH), 2.25 (d, J=11.7 Hz, 1H, 7-OH), 1.75 (d, J=12.3 Hz, 1H, 8-H), 1.33
(d, J=7.1 Hz, 3H, 16-CH3), 1.19 (s, 9H, tBu); HSQC correlation spectra
measured; HRMS (FAB): m/z: calcd for C27H29O12: 545.1659; found:
545.1641 [M+H]+.
7-(Piperidine-carbonyloxy)-10-benzyloxy-GC (26): Piperidine (2.1 mL,
22 mmol, 3 equiv) was added to a solution of 22 (5.0 mg, 7.2 mmol) in
THF (0.15 mL). The mixture was stirred for 30 min and then quenched
with aq. HCl (1 mL, 1m), extracted with EtOAc (3î) and dried with
MgSO4. The crude product was purified by flash chromatography (30
40% EtOAc/hexanes) to obtain 26 as a white solid (3.8 mg, 81%).
1H NMR (300 MHz, CDCl3): d=7.50 7.37 (m, 5HAR), 6.03 (s, 1H, 12-H),
5.43 (d, J=9.4 Hz, 1H, benzylic), 5.32 5.23 (m, 2H, 6-H and 7-H), 4.97
(s, 1H, 10-H), 4.74 (d, J=9.4 Hz, 1H, benzylic), 4.48 (d, J=7.8 Hz, 1H,
2-H), 4.21 (dd, J=7.8, 3.4 Hz, 1H, 1-H), 3.57 3.33 (m, 4H, piper.), 3.04
(q, J=7.0 Hz, 1H, 14-H), 2.79 (d, J=3.4 Hz, 1H, 1-OH), 2.78 (s, 1H, 3-
OH), 2.10 1.99 (m, 1H, 8-H), 1.71 1.40 (m, 6H, piper.), 1.30 (d, J=
7.0 Hz, 3H, 16-CH3), 1.17 (s, 9H, tBu); 13C NMR (75 MHz, CDCl3): d=
175.14, 171.12, 170.63, 152.94, 134.13, 129.73, 129.50, 128.80, 109.93, 98.37,
90.58, 83.39, 77.23, 75.33, 74.37, 74.04, 74.01, 67.57, 63.97, 48.66, 45.20
(piper.), 41.56, 32.12, 29.31, 25.89 (piper.), 25.55 (piper.), 24.22 (piper.),
7.25; HRMS (FAB): m/z: calcd for C33H40O12N: 642.2551; found:
642.2579 [M+H]+.
7-(4-Nitro-phenoxycarbonyloxy)-10-Benzyloxy-GC (22): A solution of p-
nitrophenyl chloroformate (39.6 mg, 0.195 mmol, 3 equiv) in CH2Cl2
(0.3 mL) was added to a solution of 6 (34.7 mg, 0.065 mmol) in CH2Cl2
(0.82 mL) and pyridine (187 mL, 2.31 mmol, 35 equiv). The mixture was
stirred for 50 min and then quenched with aq. HCl (2 mL, 1m), extracted
with EtOAc (3î). The combined organic layers were subsequently dried
with MgSO4. The crude product was recrystallized from CHCl3 to obtain
22 as a white crystals (27.8 mg, 61%). 1H NMR (300 MHz, CDCl3): d=
8.36 8.27 (m, 2HAR), 7.50 7.32 (m, 7HAR), 6.07 (s, 1H, 12-H), 5.47 (d,
J=9.4 Hz, 1H, benzylic), 5.47 (d, J=4.3 Hz, 1H, 6-H), 5.08 (dd, J=12.8,
4.3 Hz, 1H, 7-H), 4.99 (s, 1H, 10-H), 4.72 (d, J=9.4 Hz, 1H, benzylic),
4.51 (d, J=7.8 Hz, 1H, 2-H), 4.25 (dd, J=7.8, 3.5 Hz, 1H, 1-H), 3.05 (q,
J=7.0 Hz, 1H, 14-H), 2.88 (brs, 1H, 3-OH), 2.79 (d, J=3.5 Hz, 1H, 1-
OH), 2.18 (d, J=12.8 Hz, 1H, 8-H), 1.32 (d, J=7.0 Hz, 3H, 16-CH3),
1.23 (s, 9H, tBu).
7-Methylcarbamoyloxy-10-benzyloxy-GC (23): MeNH2 in THF (14 mL,
28 mmol, 3 equiv, 2m) was added to a solution of 22 (6.4 mg, 9.3 mmol) in
THF (0.17 mL). The mixture was stirred for 25 min and then quenched
with sat. aq. NH4Cl, extracted with EtOAc (3î) and dried with MgSO4.
The crude product was purified by flash chromatography (40 50%
EtOAc/hexanes) to obtain 23 as a white solid (4.8 mg, 88%). 1H NMR
(400 MHz, CDCl3): d=7.50 7.37 (m, 5HAR), 6.02 (s, 1H, 12-H), 5.44 (d,
J=9.4 Hz, 1H, benzylic), 5.28 (d, J=4.4 Hz, 1H, 6-H), 5.21 (dd, J=12.8,
4.4 Hz, 1H, 7-H), 4.96 (s, 1H, 10-H), 4.84 (brq, J ~4.8 Hz, 1H, -NH-),
4.73 (d, J=9.4 Hz, 1H, benzylic), 4.49 (d, J=7.8 Hz, 1H, 2-H), 4.21 (dd,
J=7.8, 3.4 Hz, 1H, 1-H), 3.03 (q, J=7.0 Hz, 1H, 14-H), 2.92 (s, 1H, 3-
OH), 2.86 (d, J=4.9 Hz, 3H, CH3), 2.80 (d, J=3.4 Hz, 1H, 1-OH), 2.00
(d, J=12.8 Hz, 1H, 8-H), 1.30 (d, J=7.0 Hz, 3H, 16-CH3), 1.16 (s, 9H,
tBu); 13C NMR (75 MHz, CDCl3): d=175.17, 171.04, 170.59, 154.68,
134.15, 129.78, 129.53, 128.82, 109.92, 98.37, 90.61, 83.41, 77.30, 75.36,
74.20, 74.10, 74.02, 67.65, 63.90, 48.50, 41.58, 32.12, 29.31, 27.72, 7.25;
HRMS (FAB): m/z: calcd for C29H34O12N: 588.2081; found: 588.2069
[M+H]+.
10-Benzyloxy-isoGC-1,6-carbonate (27):
A solution of p-nitrophenyl
chloroformate (11.0 mg, 54.6 mmol, 3 equiv) in CH2Cl2 (50 mL) was added
to a solution of 6 (9.6 mg, 18.2 mmol) in CH2Cl2 (113 mL) and iPr2EtN
(19.1 mL, 0.109 mmol, 6 equiv). The mixture was stirred for 15 min and
then quenched with aq. HCl (1 mL, 1m), extracted with EtOAc (3î) and
dried with MgSO4. The crude product was purified by flash chromatogra-
phy (30 50% EtOAc/hexanes) to obtain 27 as a white solid (9.3 mg,
92%, 82% purity). 1H NMR (300 MHz, CDCl3): d=7.45 7.28 (m,
5HAR), 5.82 (s, 1H), 5.63 (s, 1H), 5.49 (d, J=10.6 Hz, 1H), 5.05 (s, 1H),
4.88 (d, J=4.0 Hz, 1H), 4.79 (d, J=10.6 Hz, 1H), 4.76 (d, J=4.0 Hz,
1H), 4.73 (s, 1H), 3.26 (q, J=7.8 Hz, 1H), 2.96 (s, 1H), 2.28 (s, 1H), 1.35
(d, J=7.8 Hz, 3H), 1.11 (s, 9H, tBu); MS (FAB): m/z: calcd for
C28H29O12: 557.17; found: 557.56 [M+H]+.
1-Methylcarbamoyloxy-10-benzyloxy-GC (28): A solution of p-nitrophen-
yl chloroformate (10.6 mg, 52.6 mmol, 3 equiv) in CH2Cl2 (50 mL) was
added to a solution of 6 (9.3 mg, 17.6 mmol) in CH2Cl2 (110 mL) and
iPr2EtN (18.4 mL, 0.105 mmol, 6 equiv). The mixture was stirred for
15 min and MeNH2 (2m in THF, 26 mL, 52.6 mmol, 3 equiv) and THF
(80 mL) were added. The mixture was then stirred for additional 25 min
and then quenched with aq. HCl (1 mL, 1m), extracted with EtOAc (3î)
and dried with MgSO4. The crude product was purified by flash chroma-
7-tert-Butylcarbamoyloxy-10-benzyloxy-GC (24): tBuNH2 (3.4 mL,
32 mmol, 4 equiv) was added to a solution of 22 (5.5 mg, 7.9 mmol) in
THF (0.16 mL). The mixture was stirred for 40 min and then quenched
with aq. HCl (1 mL, 1m), extracted with EtOAc (3î) and dried with
MgSO4. The crude product was purified by flash chromatography (30
50% EtOAc/hexanes) to obtain 24 as a white solid (4.4 mg, 88%). The
product was further purified by reverse-phase HPLC. 1H NMR
(500 MHz, CDCl3): d=7.48 7.38 (m, 5HAR), 6.02 (s, 1H, 12-H), 5.43 (d,
J=9.5 Hz, 1H, benzylic), 5.28 (d, J=4.2 Hz, 1H, 6-H), 5.18 (dd, J=12.5,
4.2 Hz, 1H, 7-H), 4.96 (s, 1H, 10-H), 4.79 (s, 1H, -NH-), 4.75 (d, J=
9.5 Hz, 1H, benzylic), 4.50 (d, J=7.8 Hz, 1H, 2-H), 4.21 (dd, J=7.9,
tography (50 100% EtOAc/hexanes) to obtain 28 as
a white solid
(6.6 mg, 64%). 1H NMR (300 MHz, 320 K, CDCl3): d=7.42 7.2 (m,
5HAR), 5.96 (s, 1H, 12-H), 5.55 (d, J=6.0 Hz, 1H, 1-H), 5.39 (d, J=
11.5 Hz, 1H, benzylic), 5.19 (d, J=4.3 Hz, 1H, 6-H), 4.82 (s, 1H, 10-H),
4.64 (brd, J=11.5 Hz, 1H, benzylic), 4.62 (d, J=6.0 Hz, 1H, 2-H), 4.38
4.25 (m, 1H, 7-H), 4.26 (m, 1H, -NH-), 3.20 (q, J=7.2 Hz, 1H, 14-H),
2.92 (s, 1H, 3-OH), 2.29 (brd, J ~4.1 Hz, 3H, CH3), 2.16 (d, J=11.5 Hz,
1514
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 1507 1518

Ginkgolides and Glycine Receptors
1507 1518
1H, 7-OH), 1.69 (d, J=12.3 Hz, 1H, 8-H), 1.31 (d, J=7.2 Hz, 3H, 16-
CH3), 1.15 (s, 9H, tBu); HSQC correlation spectra was measured;
HRMS (FAB): m/z: calcd for C29H34O12N: 588.2081; found: 588.2103
[M+H]+.
CH2Cl2 (0.53 mL) and pyridine (121 mL, 1.50 mmol, 18 equiv) at 08C. The
mixture was allowed to warm up slowly to room temperature while stir-
ring. After 2.5 h the reaction was quenched with aq. HCl (2 mL, 1m), ex-
tracted with EtOAc (3î) and dried with MgSO4. The crude product was
purified by flash chromatography (30 50% EtOAc/hexanes) to obtain 32
as a white powder (42.6 mg, 69%) and unreacted starting material 7
(9.5 mg, 20%). 1H NMR (400 MHz, CDCl3): d=8.35 8.27 (m, 2HAR),
7.46 7.38 (m, 2HAR), 7.35 7.28 (m, 2HAR), 6.95 6.88 (m, 2HAR), 6.06 (s,
1H, 12-H), 5.45 (d, J=4.3 Hz, 1H, 6-H), 5.38 (d, J=9.3 Hz, 1H, benzyl-
ic), 5.05 (dd, J=12.8, 4.3 Hz, 1H, 7-H), 4.98 (s, 1H, 10-H), 4.66 (d, J=
9.3 Hz, 1H, benzylic), 4.51 (d, J=7.8 Hz, 1H, 2-H), 4.25 (dd, J=7.8,
3.5 Hz, 1H, 1-H), 3.80 (s, 3H, OMe), 3.06 (q, J=7.0 Hz, 1H, 14-H), 3.04
(s, 1H, 3-OH), 2.87 (d, J=3.5 Hz, 1H, 1-OH), 2.17 (d, J=12.8 Hz, 1H, 8-
H), 1.30 (d, J=7.0 Hz, 3H, 16-CH3), 1.22 (s, 9H, tBu); 13C NMR
(100 MHz, CDCl3): d=174.90, 170.11, 170.07, 160.41, 154.72, 150.82,
145.52, 130.36, 125.94, 125.28, 121.48, 114.71, 109.65, 98.23, 90.48, 83.43,
78.17, 75.69, 74.93, 73.90, 73.72, 67.77, 63.85, 55.38, 48.48, 41.70, 32.24,
29.42, 7.46.
1-tert-Butylcarbamoyloxy-10-benzyloxy-GC (29): A solution of p-nitro-
phenyl chloroformate (4.2 mg, 21 mmol, 3 equiv) in CH2Cl2 (20 mL) was
added to a solution of 6 (3.7 mg, 7.0 mmol) in CH2Cl2 (50 mL) and
iPr2EtN (7.3 mL, 42 mmol, 6 equiv). The mixture was stirred for 15 min
and tBuNH2 (7.4 mL, 70 mmol, 10 equiv) and THF (40 mL) were added.
The mixture was then stirred for additional 12 h and then quenched with
aq. HCl (1 mL, 1m), extracted with EtOAc (3î) and dried with MgSO4.
The crude product was purified by flash chromatography (40 50%
EtOAc/hexanes) to obtain 29 as a white solid (2.6 mg, 59%). 1H NMR
(300 MHz, CDCl3): d=7.40 7.22 (m, 5HAR), 5.93 (s, 1H, 12-H), 5.55 (d,
J=5.1 Hz, 1H, 1-H), 5.32 (d, J=12.3 Hz, 1H, benzylic), 5.22 (d, J=
4.3 Hz, 1H, 6-H), 4.81 (brd, J=11.5 Hz, 1H, benzylic), 4.79 (s, 1H, 10-
H), 4.67 (d, J=5.1 Hz, 1H, 2-H), 4.53 (brs, 1H, -NH-), 4.36 4.24 (m, 1H,
7-H), 3.21 (q, J=7.3 Hz, 1H, 14-H), 3.17 (brs, 1H, 3-OH), 2.13 (brd, J=
12.0 Hz, 1H, 7-OH), 1.65 (d, J=12.3 Hz, 1H, 8-H), 1.32 (d, J=7.3 Hz,
3H, 16-CH3), 1.12 (s, 9H, tBu), 1.03 (s, 9H, tBu); 13C NMR (100 MHz,
CDCl3): d=174.20, 170.34, 169.47, 151.09, 135.55, 128.12 (2), 127.85,
108.52, 99.96, 91.90, 84.08, 80.10, 75.19, 74.94, 74.61, 66.53, 65.05, 50.75,
50.43, 40.94, 32.16, 28.97, 28.49, 8.57; HRMS (FAB): m/z: calcd for
C32H40O12N: 630.2551; found: 630.2554 [M+H]+.
7-Methylcarbamoyloxy-10-(4-methoxy-benzyloxy)-GC (33): The com-
pound was synthesized from 32 according to the procedure for 23. Prod-
uct was obtained as a white solid (74%). 1H NMR (500 MHz, CDCl3):
d=7.36 (d, J=8.5 Hz, 2HAR), 6.95 (d, J=8.5 Hz, 2HAR), 6.01 (s, 1H, 12-
H), 5.35 (d, J=9.3 Hz, 1H, benzylic), 5.26 (d, J=4.3 Hz, 1H, 6-H), 5.19
(dd, J=12.8, 4.4 Hz, 1H, 7-H), 4.94 (s, 1H, 10-H), 4.83 (brq, J ~4.8 Hz,
1H, -NH-), 4.67 (d, J=9.3 Hz, 1H, benzylic), 4.49 (d, J=7.8 Hz, 1H, 2-
H), 4.20 (dd, J=7.8, 3.3 Hz, 1H, 1-H), 3.82 (s, 3H, OMe), 3.03 (q, J=
7.0 Hz, 1H, 14-H), 2.90 (s, 1H, 3-OH), 2.89 2.80 (m, 4H, CH3 and 1-
OH), 1.99 (d, J=12.8 Hz, 1H, 8-H), 1.29 (d, J=7.0 Hz, 3H, 16-CH3),
1.15 (s, 9H, tBu); 13C NMR (100 MHz, CDCl3): d=174.69, 170.52, 170.15,
160.10, 154.19, 130.13, 125.81, 114.45, 109.55, 98.01, 90.31, 83.15, 74.78,
73.96, 73.77, 73.40, 67.43, 63.70, 55.14, 48.35, 41.47, 32.01, 29.21, 27.61,
7.24; HRMS (FAB): m/z: calcd for C30H34O13N: 616.2030; found:
616.2056 [MÀH]+.
7-tert-Butylcarbamoyloxy-10-(4-methoxy-benzyloxy)-GC (34): The com-
pound was synthesized from 32 according to the procedure for 24. Prod-
uct was obtained as a white solid (77%). 1H NMR (400 MHz, CDCl3):
d=7.41 7.35 (m, 2HAR), 6.99 6.91 (m, 2HAR), 6.01 (s, 1H, 12-H), 5.34 (d,
J=9.3 Hz, 1H, benzylic), 5.26 (d, J=4.3 Hz, 1H, 6-H), 5.15 (dd, J=12.8,
4.2 Hz, 1H, 7-H), 4.94 (s, 1H, 10-H), 4.81 (s, 1H, -NH-), 4.69 (d, J=
9.3 Hz, 1H, benzylic), 4.50 (d, J=7.9 Hz, 1H, 2-H), 4.20 (dd, J=7.9,
3.4 Hz, 1H, 1-H), 3.82 (s, 3H, OMe), 3.03 (q, J=7.0 Hz, 1H, 14-H), 2.94
(s, 1H, 3-OH), 2.88 (d, J=3.4 Hz, 1H, 1-OH), 1.97 (d, J=12.8 Hz, 1H, 8-
H), 1.35 (s, 9H, tBu), 1.29 (d, J=7.0 Hz, 3H, 16-CH3), 1.15 (s, 9H, tBu);
13C NMR (75 MHz, CDCl3): d=175.29, 171.18, 170.78, 160.56, 152.11,
130.63, 126.24, 114.76, 109.96, 98.34, 90.58, 83.42, 77.55, 75.02, 74.01,
73.62, 73.35, 67.61, 63.90, 55.30, 50.89, 48.60, 41.60, 32.08, 29.31, 28.79,
7.27; HRMS (FAB): m/z: calcd for C33H41O13N: 659.2578; found:
659.2582 [M]+.
1-(Morpholine-4-carbonyloxy)-10-benzyloxy-GC (30): A solution of p-ni-
trophenyl chloroformate (7.2 mg, 36 mmol, 3 equiv) in CH2Cl2 (50 mL)
was added to a solution of 6 (6.3 mg, 12.0 mmol) in CH2Cl2 (60 mL) and
iPr2EtN (12.5 mL, 72 mmol, 6 equiv). The mixture was stirred for 15 min
and morpholine (6.3 mL, 72 mmol, 6 equiv) was added. The mixture was
then stirred for additional 1 h and then quenched with aq. HCl (1 mL,
1m), extracted with EtOAc (3î) and dried with MgSO4. The crude prod-
uct was purified by flash chromatography (50 100% EtOAc/hexanes) to
obtain 30 as a white solid (6.0 mg, 78%). 1H NMR (400 MHz, CDCl3):
d=7.41 7.31 (m, 3HAR), 7.29 7.21 (m, 2HAR), 5.99 (s, 1H, 12-H), 5.60 (d,
J=5.6 Hz, 1H, 1-H), 5.40 (d, J=11.5 Hz, 1H, benzylic), 5.15 (d, J=
4.4 Hz, 1H, 6-H), 4.85 (s, 1H, 10-H), 4.71 (d, J=5.6 Hz, 1H, 2-H), 4.62
(d, J=11.5 Hz, 1H, benzylic), 4.38 4.28 (m, 1H, 7-H), 3.60 (s, 1H, 3-
OH), 3.5 3.2 (m, 6H, morph.), 3.21 (q, J=7.2 Hz, 1H, 14-H), 2.78 2.67
(m, 1H, morph.), 2.50 (d, J=11.7 Hz, 1H, 7-OH), 2.49 2.38 (m, 1H,
morph.), 1.72 (d, J=12.3 Hz, 1H, 8-H), 1.32 (d, J=7.2 Hz, 3H, 16-CH3),
1.18 (s, 9H, tBu); 13C NMR (75 MHz, CDCl3): d=175.04, 170.60, 169.99,
152.15, 136.20, 128.65, 128.42, 127.44, 109.11, 99.90, 92.16, 84.12, 80.21,
75.85, 75.65, 73.24, 66.51, 66.15, 65.87, 65.07, 50.40, 43.73, 43.48, 41.19,
32.40, 29.16, 8.30; HRMS (FAB): m/z: calcd for C32H38O13N: 644.2343;
found: 644.2355 [M+H]+.
1-(Piperidine-carbonyloxy)-10-benzyloxy-GC (31): A solution of p-nitro-
phenyl chloroformate (13 mg, 64 mmol, 3 equiv) in CH2Cl2 (80 mL) was
added to a solution of 6 (11.3 mg, 21.3 mmol) in CH2Cl2 (112 mL) and
iPr2EtN (22.4 mL, 128 mmol, 6 equiv). The mixture was stirred for 15 min
and piperidine (12.6 mL, 128 mmol, 6 equiv) and THF (80 mL) were
added. The mixture was then stirred for additional 40 min and then
quenched with aq. HCl (1 mL, 1m), extracted with EtOAc (3î) and
dried with MgSO4. The crude product was purified by flash chromatogra-
phy (35 70% EtOAc/hexanes) to obtain 31 as a white solid (6.8 mg,
50%). 1H NMR (400 MHz, CDCl3): d=7.39 7.28 (m, 3HAR), 7.28 7.21
(m, 2HAR), 5.97 (s, 1H, 12-H), 5.57 (d, J=5.3 Hz, 1H, 1-H), 5.38 (d, J=
11.5 Hz, 1H, benzylic), 5.14 (d, J=4.4 Hz, 1H, 6-H), 4.84 (s, 1H, 10-H),
4.72 (d, J=5.3 Hz, 1H, 2-H), 4.65 (d, J=11.5 Hz, 1H, benzylic), 4.37
4.28 (m, 1H, 7-H), 3.57 (s, 1H, 3-OH), 3.50 3.38 (m, 1H, piper.), 3.35
3.23 (m, 1H, piper.), 3.22 (q, J=7.3 Hz, 1H, 14-H), 2.60 2.49 (m, 1H,
piper.), 2.47 2.37 (m, 1H, piper.), 2.36 (d, J=12.0 Hz, 1H, 7-OH), 1.70
(d, J=12.3 Hz, 1H, 8-H), 1.61 1.50 (m, 1H, piper.), 1.45 1.25 (m, 5H,
piper.), 1.32 (d, J=7.3 Hz, 3H, 16-CH3), 1.16 (s, 9H, tBu); 13C NMR
(100 MHz, CDCl3): d=175.00, 170.80, 170.02, 152.22, 136.16, 128.54,
128.17, 127.75, 108.98, 100.23, 92.23, 84.26, 80.39, 76.07, 75.64, 75.44,
73.12, 66.80, 65.17, 50.47, 44.64, 44.49, 41.15, 32.38, 29.17, 25.52, 24.96,
23.89, 8.53; HRMS (FAB): m/z: calcd for C33H40O12N: 642.2551; found:
642.2521 [M+H]+.
7-(Morpholine-4-carbonyloxy)-10-(4-methoxy-benzyloxy)-GC (35): The
compound was synthesized from 32 according to the procedure for 25.
Product was obtained as
a
white solid (90%). 1H NMR (300 MHz,
CDCl3): d=7.36 (d, J=8.6 Hz, 2HAR), 6.95 (d, J=8.6 Hz, 2HAR), 6.02 (s,
1H, 12-H), 5.36 (d, J=9.3 Hz, 1H, benzylic), 5.30 5.19 (m, 2H, 6-H and
7-H), 4.95 (s, 1H, 10-H), 4.68 (d, J=9.3 Hz, 1H, benzylic), 4.48 (d, J=
7.8 Hz, 1H, 2-H), 4.21 (d, J=7.8 Hz, 1H, 1-H), 3.82 (s, 3H, OMe), 3.78
3.33 (m, 8H, morph.), 3.04 (q, J=7.0 Hz, 1H, 14-H), 2.85 (brs, 2H, 3-
OH and 1-OH), 2.09 1.99 (m, 1H, 8-H), 1.30 (d, J=7.0 Hz, 3H, 16-CH3),
1.16 (s, 9H, tBu); 13C NMR (100 MHz, CDCl3): d=174.59, 170.48, 170.08,
160.11, 152.52, 130.13, 125.79, 114.45, 109.53, 98.04, 90.29, 83.15, 76.92,
74.76, 74.47, 73.76, 73.40, 67.38, 66.36 (morph.), 66.29 (morph.), 63.78,
55.14, 48.54, 44.35 (morph.), 44.08 (morph.), 41.45, 32.04, 29.23, 7.24;
HRMS (FAB): m/z: calcd for C33H39O14N: 673.2371; found: 673.2402
[M]+.
7-(Piperidine-carbonyloxy)-10-(4-methoxy-benzyloxy)-GC (36): The com-
pound was synthesized from 32 according to the procedure for 26. Prod-
uct was obtained as a white solid (86%). 1H NMR (400 MHz, CDCl3):
d=7.36 (d, J=8.7 Hz, 2HAR), 6.94 (d, J=8.7 Hz, 2HAR), 6.01 (s, 1H, 12-
H), 5.35 (d, J=9.3 Hz, 1H, benzylic), 5.29 5.20 (m, 2H, 6-H and 7-H),
4.95 (s, 1H, 10-H), 4.68 (d, J=9.3 Hz, 1H, benzylic), 4.48 (d, J=7.9 Hz,
1H, 2-H), 4.20 (dd, J=7.9, 3.4 Hz, 1H, 1-H), 3.81 (s, 3H, OMe), 3.53
3.37 (m, 4H, piper.), 3.04 (q, J=7.0 Hz, 1H, 14-H), 2.95 (s, 1H, 3-OH),
7-(4-Nitro-phenoxycarbonyloxy)-10-(4-methoxy-benzyloxy)-GC (32):
A
solution of p-nitrophenyl chloroformate (34.2 mg, 0.170 mmol, 2 equiv) in
CH2Cl2 (0.2 mL) was added to a solution of 7 (47.6 mg, 0.085 mmol) in
1515
Chem. Eur. J. 2004, 10, 1507 1518
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

K. Nakanishi, K. Str˘mgaard et al.
FULL PAPER
2.86 (d, J=3.4 Hz, 1H, 1-OH), 2.03 (d, J=12.2 Hz, 1H, 8-H), 1.68 1.42
(m, 6H, piper.), 1.30 (d, J=7.0 Hz, 3H, 16-CH3), 1.16 (s, 9H, tBu);
13C NMR (100 MHz, CDCl3): d=174.96, 170.85, 170.47, 160.31, 152.74,
130.39, 126.09, 114.68, 109.85, 98.32, 90.59, 83.39, 77.41, 75.01, 74.44,
74.04, 73.60, 67.62, 64.03, 55.38, 48.80, 45.25 (piper.), 41.74, 32.27, 29.47,
26.07 (piper.), 25.71 (piper.), 24.39 (piper.), 7.51; HRMS (FAB): m/z:
calcd for C34H40O13N: 670.2500; found: 670.2526 [MÀH]+.
7-Methylcarbamoyloxy-GC (42): An aq. solution of (NH4)2Ce(NO3)6
(10.6 mL, 17.3 mmol, 2 equiv, 1.63m) was added to
a solution of 33
(5.3 mg, 8.7 mmol) in acetonitrile (108 mL) and CHCl3 (35 mL). The mix-
ture was stirred for 1.5 h, aq. solution of (NH4)2Ce(NO3)6 (5.3 mL,
8.7 mmol, 1 equiv, 1.63m) was added and mixture was further stirred for
12 h. Volatiles were removed under reduced pressure and residue was pu-
rified by flash chromatography (40 99% EtOAc/1% AcOH/hexanes) to
obtain 42 as a white powder (3.0 mg, 69%). 1H NMR (300 MHz, 315 K,
CD3OD): d=6.11 (s, 1H, 12-H), 5.32 (d, J=4.3 Hz, 1H, 6-H), 5.18 (dd,
J=12.8, 4.3 Hz, 1H, 7-H), 5.13 (s, 1H, 10-H), 4.54 (d, J=7.6 Hz, 1H, 2-
H), 4.18 (d, J=7.6 Hz, 1H, 1-H), 3.00 (q, J=7.0 Hz, 1H, 14-H), 2.74 (s,
3H, CH3), 2.00 (d, J=12.9 Hz, 1H, 8-H), 1.22 (d, J=7.0 Hz, 3H, 16-
CH3), 1.14 (s, 9H, tBu); HSQC correlation spectra measured; HRMS
(FAB): m/z: calcd for C22H28O12N: 498.1612; found: 498.1633 [M+H]+.
1-Methylcarbamoyloxy-10-(4-methoxy-benzyloxy)-GC (38): The com-
pound was synthesized from 7 according to the procedure for 28. Product
1
was obtained as a white solid (67%). H NMR (400 MHz, CDCl3, 330 K):
d=7.25 7.15 (m, 2HAR), 6.90 6.80 (m, 2HAR), 5.94 (s, 1H, 12-H), 5.53 (d,
J=5.7 Hz, 1H, 1-H), 5.24 (d, J=11.1 Hz, 1H, benzylic), 5.18 (d, J=
4.3 Hz, 1H, 6-H), 4.79 (s, 1H, 10-H), 4.69 4.54 (m, 2H, 2-H and benzyl-
ic), 4.39 (brs, 1H, -NH-), 4.32 4.21 (m, 1H, 7-H), 3.80 (s, 3H, OMe),
3.19 (q, J=7.2 Hz, 1H, 14-H), 3.01 (s, 1H, 3-OH), 2.42 (brs, 3H, Me),
2.19 (d, J=10.8 Hz, 1H, 7-OH), 1.68 (d, J=12.3 Hz, 1H, 8-H), 1.30 (d,
J=7.2 Hz, 3H, 16-CH3), 1.13 (s, 9H, tBu); 13C NMR (75 MHz, CD3OD,
320 K): d=177.90, 172.80, 172.52, 161.06, 156.56, 130.42, 114.94, 114.84,
110.68, 102.23, 94.34, 85.44, 81.36, 77.21, 77.03, 76.12, 73.68, 68.12, 66.20,
55.86, 51.35, 42.59, 33.17, 29.63, 27.31, 9.42; HRMS (FAB): m/z: calcd for
C30H34O13N: 616.2030; found: 616.2028 [MÀH]+.
7-tert-Butylcarbamoyloxy-GC (43): An aq. solution of (NH4)2Ce(NO3)6
(10.6 mL, 17.3 mmol, 2 equiv, 1.63m) was added to
a solution of 34
(5.7 mg, 8.6 mmol) in acetonitrile (108 mL) and CHCl3 (35 mL). The mix-
ture was stirred for 1.5 h, aq. solution of (NH4)2Ce(NO3)6 (5.3 mL,
8.7 mmol, 1 equiv, 1.63m) was added and mixture was further stirred for
12 h. Volatiles were removed under reduced pressure and residue was pu-
rified by flash chromatography (40 70% EtOAc/1% AcOH/hexanes) to
1
1-tert-Butylcarbamoyloxy-10-(4-methoxy-benzyloxy)-GC (39): The com-
pound was synthesized from 7 according to the procedure for 29. Product
was obtained as a white solid (60%). 1H NMR (400 MHz, CDCl3): d=
7.23 (d, J=8.6 Hz, 2HAR), 6.86 (d, J=8.6 Hz, 2HAR), 5.91 (s, 1H, 12-H),
5.55 (d, J=4.6 Hz, 1H, 1-H), 5.21 (d, J=4.3 Hz, 1H, 6-H), 5.15 (d, J=
11.8 Hz, 1H, benzylic), 4.82 (brd, J=11.8 Hz, 1H, benzylic), 4.75 (s, 1H,
10-H), 4.67 (d, J=5.0 Hz, 1H, 2-H), 4.62 (brs, 1H, -NH-), 4.30 4.19 (m,
1H, 7-H), 3.80 (s, 3H, OMe), 3.23 (brs, 1H, 3-OH), 3.20 (q, J=7.3 Hz,
1H, 14-H), 2.17 (d, J=11.8 Hz, 1H, 7-OH), 1.63 (d, J=12.3 Hz, 1H, 8-
H), 1.32 (d, J=7.3 Hz, 3H, 16-CH3), 1.19 (s, 9H, tBu), 1.01 (s, 9H, tBu);
13C NMR (75 MHz, CDCl3): d=174.94, 171.01, 170.25, 159.72, 151.70,
130.14, 127.77, 113.88, 108.79, 100.34, 92.26, 84.41, 80.41, 75.27, 73.96,
72.16, 66.83, 65.29, 55.31, 50.92, 50.51, 41.06, 32.20, 29.02, 28.72, 8.68;
HRMS (FAB): m/z: calcd for C33H40O13N: 658.2500; found: 658.2516
[MÀH]+.
obtain 43 as a white powder (3.7 mg, 80%). H NMR (400 MHz, CDCl3):
d=6.01 (brs, 1H, OH), 5.98 (s, 1H, 12-H), 5.42 (brs, 1H, 6-H), 5.16 (dd,
J=12.8, 4.1 Hz, 1H, 7-H), 5.14 (s, 1H, 10-H), 4.96 (s, 1H, -NH-), 4.69 (d,
J=7.9 Hz, 1H, 2-H), 4.32 (brd, J=7.9 Hz, 1H, 1-H), 4.23 (brs, 2H, OH),
3.14 (brq, J=7.1 Hz, 1H, 14-H), 1.98 (d, J=12.8 Hz, 1H, 8-H), 1.31 (s,
9H, tBu), 1.27 (d, J=7.1 Hz, 3H, 16-CH3), 1.10 (s, 9H, tBu); HSQC cor-
relation spectra measured; HRMS (FAB): m/z: calcd for C25H34O12N:
540.2081; found: 540.2098 [M+H]+.
7-(Morpholine-4-carbonyloxy)-GC
(44):
An
aq.
solution
of
(NH4)2Ce(NO3)6 (10.6 mL, 17.3 mmol, 2 equiv, 1.63m) was added to a solu-
tion of 35 (5.8 mg, 8.7 mmol) in acetonitrile (108 mL) and CHCl3 (35 mL).
The mixture was stirred for 1.5 h, aq. solution of (NH4)2Ce(NO3)6
(5.3 mL, 8.7 mmol, 1 equiv, 1.63m) was added and mixture was further stir-
red for 12 h. Volatiles were removed under reduced pressure and residue
was purified by flash chromatography (50 99% EtOAc/1% AcOH/hex-
1-(Morpholine-4-carbonyloxy)-10-(4-methoxy-benzyloxy)-GC (40): The
compound was synthesized from 7 according to the procedure for 30.
1
anes) to obtain 44 as a white powder (2.9 mg, 60%). H NMR (400 MHz,
CD3OD): d=6.14 (s, 1H, 12-H), 5.34 (d, J=4.4 Hz, 1H, 6-H), 5.24 (dd,
J=12.8, 4.4 Hz, 1H, 7-H), 5.15 (s, 1H, 10-H), 4.54 (d, J=7.6 Hz, 1H, 2-
H), 4.18 (d, J=7.6 Hz, 1H, 1-H), 3.73 3.37 (m, 8H, morph.), 3.00 (q, J=
7.1 Hz, 1H, 14-H), 2.06 (d, J=12.8 Hz, 1H, 8-H), 1.22 (d, J=7.1 Hz, 3H,
16-CH3), 1.15 (s, 9H, tBu); HSQC correlation spectra measured; HRMS
(FAB): m/z: calcd for C25H32O13N: 554.1874; found: 554.1874 [M+H]+.
Product was obtained as
a
white solid (75%). 1H NMR (400 MHz,
CDCl3): d=7.20 (d, J=8.5 Hz, 2HAR), 6.88 (d, J=8.5 Hz, 2HAR), 5.97 (s,
1H, 12-H), 5.57 (d, J=5.3 Hz, 1H, 1-H), 5.23 (d, J=11.0 Hz, 1H, benzyl-
ic), 5.11 (d, J=4.3 Hz, 1H, 6-H), 4.82 (s, 1H, 10-H), 4.71 (d, J=5.3 Hz,
1H, 2-H), 4.62 (d, J=11.0 Hz, 1H, benzylic), 4.32 4.21 (m, 1H, 7-H),
3.82 (s, 3H, OMe), 3.57 (s, 1H, 3-OH), 3.54 3.33 (m, 5H, morph.), 3.31
3.18 (m, 1H, morph.), 3.21 (q, J=7.2 Hz, 1H, 14-H), 2.89 2.66 (m, 2H,
morph.), 2.39 (d, J=11.7 Hz, 1H, 7-OH), 1.69 (d, J=12.3 Hz, 1H, 8-H),
1.32 (d, J=7.2 Hz, 3H, 16-CH3), 1.15 (s, 9H, tBu); 13C NMR (75 MHz,
CDCl3): d=175.06, 170.66, 170.21, 159.75, 152.38, 129.64, 128.01, 113.97,
108.99, 100.08, 92.15, 84.25, 80.20, 76.28, 75.54, 74.97, 72.83, 66.68, 66.21
(morph.), 65.94 (morph.), 65.12, 55.41, 50.41, 43.84 (morph.), 41.16, 32.33,
29.14, 8.49; HRMS (FAB): m/z: calcd for C33H38O14N: 672.2292; found:
672.2307 [MÀH]+.
1-(Piperidine-carbonyloxy)-10-(4-methoxy-benzyloxy)-GC (41): The com-
pound was synthesized from 7 according to the procedure for 31. Product
was obtained as a white solid (53%). 1H NMR (400 MHz, CDCl3): d=
7.20 (d, J=8.6 Hz, 2HAR), 6.87 (d, J=8.6 Hz, 2HAR), 5.95 (s, 1H, 12-H),
5.54 (d, J=5.0 Hz, 1H, 1-H), 5.22 (d, J=11.0 Hz, 1H, benzylic), 5.10 (d,
J=4.4 Hz, 1H, 6-H), 4.80 (s, 1H, 10-H), 4.72 (d, J=5.0 Hz, 1H, 2-H),
4.64 (d, J=11.0 Hz, 1H, benzylic), 4.32 4.22 (m, 1H, 7-H), 3.81 (s, 3H,
OMe), 3.55 (s, 1H, 3-OH), 3.52 3.40 (m, 1H, piper.), 3.32 3.19 (m, 1H,
piper.), 3.22 (q, J=7.3 Hz, 1H, 14-H), 2.77 2.56 (m, 2H, piper.), 2.25 (d,
J=12.0 Hz, 1H, 7-OH), 1.68 (d, J=12.3 Hz, 1H, 8-H), 1.63 1.50 (m, 1H,
piper.), 1.49 1.29 (m, 5H, piper.), 1.32 (d, J=7.3 Hz, 3H, 16-CH3), 1.14
(s, 9H, tBu); 13C NMR (75 MHz, CDCl3): d=174.88, 170.81, 170.20,
159.63, 152.37, 129.89, 128.07, 113.88, 108.86, 100.36, 92.18, 84.36, 80.38,
76.45, 75.56, 74.77, 72.68, 66.95, 65.25, 55.36, 50.53, 44.84 (piper.), 44.62
(piper.), 41.11, 32.31, 29.15, 25.56 (piper.), 25.09 (piper.), 23.98 (piper.),
8.68; HRMS (FAB): m/z: calcd for C34H40O13N: 670.2500; found:
670.2510 [MÀH]+.
7-(Piperidine-carbonyloxy)-GC (45): An aq. solution of (NH4)2Ce(NO3)6
(10.6 mL, 17.3 mmol, 2 equiv, 1.63m) was added to
a solution of 36
(5.8 mg, 8.6 mmol) in acetonitrile (108 mL) and CHCl3 (35 mL). The mix-
ture was stirred for 1.5 h, aq. solution of (NH4)2Ce(NO3)6 (5.3 mL,
8.7 mmol, 1 equiv, 1.63m) was added and mixture was further stirred for
12 h. Volatiles were removed under reduced pressure and residue was pu-
rified by flash chromatography (40 70% EtOAc/1% AcOH/hexanes) to
1
obtain 45 as a white powder (3.0 mg, 64%). H NMR (400 MHz, CDCl3):
d=6.21 (brs, 1H, OH), 5.98 (s, 1H, 12-H), 5.41 (brs, 1H, 6-H), 5.25 (dd,
J=12.8, 4.3 Hz, 1H, 7-H), 5.14 (s, 1H, 10-H), 4.68 (d, J=7.9 Hz, 1H, 2-
H), 4.36 (brs, 1H, OH), 4.32 (brd, J=7.9 Hz, 1H, 1-H), 3.55 3.26 (m,
4H, piper.), 3.15 (m, 1H, 14-H), 2.04 (d, J=12.8 Hz, 1H, 8-H), 1.75 1.40
(m, 6H, piper.), 1.26 (d, J=7.0 Hz, 3H, 16-CH3), 1.11 (s, 9H, tBu);
HSQC correlation spectra measured; HRMS (FAB): m/z: calcd for
C26H34O12N: 552.2081; found: 552.2067 [M+H]+.
1-Methylcarbamoyloxy-GC (46): An aq. solution of (NH4)2Ce(NO3)6
(6.9 mL, 11.2 mmol, 2 equiv, 1.63m) was added to a solution of 38 (3.5 mg,
5.6 mmol) in acetonitrile (70 mL) and CHCl3 (23 mL). The mixture was
stirred for 6.5 h, aq. solution of (NH4)2Ce(NO3)6 (6.9 mL, 11.2 mmol,
2 equiv, 1.63m) was added and mixture was further stirred for 12 h. Vola-
tiles were removed under reduced pressure and residue was purified by
flash chromatography (70 99% EtOAc/1% AcOH/hexanes) to obtain 46
1
as a white powder (2.4 mg, 86%). H NMR (400 MHz, CD3OD): d=6.06
(s, 1H, 12-H), 5.46 (d, J=5.3 Hz, 1H, 1-H), 5.22 (d, J=4.1 Hz, 1H, 6-H),
5.07 (s, 1H, 10-H), 4.66 (d, J=5.5 Hz, 1H, 2-H), 4.31 (dd, J=12.6,
4.1 Hz, 1H, 7-H), 3.10 (q, J=7.2 Hz, 1H, 14-H), 2.83 2.68 (m, 3H, Me),
1.78 (d, J=12.5 Hz, 1H, 8-H), 1.27 (d, J=7.2 Hz, 3H, 16-CH3), 1.22 (s,
1516
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 1507 1518

Ginkgolides and Glycine Receptors
1507 1518
9H, tBu); HSQC correlation spectra measured; HRMS (FAB): m/z:
calcd for C22H28O12N: 498.1612; found: 498.1618 [M+H]+.
Acknowledgments
We are grateful to Dr. Yasuhiro Itagaki for performing HRMS, Dirk A.
Lichtblau, PhD, for purification of GC, Stine B. Vogensen, PhD and Mr.
Nathan E. Fishkin for the discussions. We thank the following for finan-
cial support: NIH grant MH068817, Memory Pharmaceuticals Corp., the
Alfred Bader Foundation (to S.J.), the Alfred Benzon Foundation (to
K.S.) and the Lundbeck Foundation (to A.A.J.).
1-tert-Butylcarbamoyloxy-GC (47): An aq. solution of (NH4)2Ce(NO3)6
(6.9 mL, 11.2 mmol, 2 equiv, 1.63m) was added to a solution of 39 (3.7 mg,
5.6 mmol) in acetonitrile (70 mL) and CHCl3 (23 mL). The mixture was
stirred for 6 h, aq. solution of (NH4)2Ce(NO3)6 (6.9 mL, 11.2 mmol,
2 equiv, 1.63m) was added and mixture was further stirred for 12 h. Vola-
tiles were removed under reduced pressure and residue was purified by
flash chromatography (40 70% EtOAc/hexanes) to obtain 47 as a white
1
powder (2.5 mg, 84%). H NMR (400 MHz, CD3OD): d=6.05 (s, 1H, 12-
H), 5.45 (d, J=5.1 Hz, 1H, 1-H), 5.28 (d, J=4.2 Hz, 1H, 6-H), 5.06 (s,
1H, 10-H), 4.64 (d, J=5.1 Hz, 1H, 2-H), 4.33 (dd, J=12.4, 4.2 Hz, 1H, 7-
H), 3.10 (q, J=7.3 Hz, 1H, 14-H), 1.77 (d, J=12.4 Hz, 1H, 8-H), 1.34 (s,
9H, tBu), 1.27 (d, J=7.3 Hz, 3H, 16-CH3), 1.22 (s, 9H, tBu); HSQC cor-
relation spectra measured; HRMS (FAB): m/z: calcd for C25H34O12N:
540.2081; found: 540.2075 [M+H]+.
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1-(Morpholine-4-carbonyloxy)-GC
(48):
An
aq.
solution
of
(NH4)2Ce(NO3)6 (11.8 mL, 19.2 mmol, 2 equiv, 1.63m) was added to a solu-
tion of 40 (6.5 mg, 9.6 mmol) in acetonitrile (120 mL) and CHCl3 (39 mL).
The mixture was stirred for 6.5 h, aq. solution of (NH4)2Ce(NO3)6
(11.8 mL, 19.2 mmol, 2 equiv, 1.63m) was added and mixture was further
stirred for 12 h. Volatiles were removed under reduced pressure and resi-
due was purified by flash chromatography (70 99% EtOAc/1% AcOH/
hexanes) to obtain 48 as
a
white powder (4.3 mg, 80%). 1H NMR
(400 MHz, CD3OD): d=6.10 (s, 1H, 12-H), 5.39 (d, J=6.6 Hz, 1H, 1-H),
5.22 (d, J=4.2 Hz, 1H, 6-H), 5.09 (s, 1H, 10-H), 4.74 (d, J=6.6 Hz, 1H,
2-H), 4.28 (dd, J=12.4, 4.2 Hz, 1H, 7-H), 3.76 3.62 (m, 4H, morph.),
3.58 3.38 (m, 4H, morph.), 3.12 (q, J=7.1 Hz, 1H, 14-H), 1.79 (d, J=
12.4 Hz, 1H, 8-H), 1.28 (d, J=7.1 Hz, 3H, 16-CH3), 1.22 (s, 9H, tBu);
HSQC correlation spectra measured; HRMS (FAB): m/z: calcd for
C25H32O13N: 554.1874; found: 554.1874 [M+H]+.
1-(Piperidine-carbonyloxy)-GC (49): An aq. solution of (NH4)2Ce(NO3)6
(6.9 mL, 11.2 mmol, 2 equiv, 1.63m) was added to a solution of 41 (3.8 mg,
5.6 mmol) in acetonitrile (70 mL) and CHCl3 (23 mL). The mixture was
stirred for 6.5 h, aq. solution of (NH4)2Ce(NO3)6 (6.9 mL, 11.2 mmol,
2 equiv, 1.63m) was added and mixture was further stirred for 12 h. Vola-
tiles were removed under reduced pressure and residue was purified by
flash chromatography (50 100% EtOAc/hexanes) to obtain 49 as a white
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1
powder (2.5 mg, 79%). H NMR (400 MHz, CD3OD): d=6.09 (s, 1H, 12-
H), 5.40 (d, J=6.4 Hz, 1H, 1-H), 5.22 (d, J=4.2 Hz, 1H, 6-H), 5.08 (s,
1H, 10-H), 4.71 (d, J=6.4 Hz, 1H, 2-H), 4.32 (dd, J=12.4, 4.2 Hz, 1H, 7-
H), 3.68 3.50 (m, 2H, piper.), 3.46 3.20 (m, 2H, piper.), 3.12 (q, J=
7.2 Hz, 1H, 14-H), 1.79 (d, J=12.4 Hz, 1H, 8-H), 1.75 1.52 (m, 6H,
piper.), 1.28 (d, J=7.2 Hz, 3H, 16-CH3), 1.22 (s, 9H, tBu); HSQC corre-
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552.2081; found: 552.2061 [M+H]+.
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human homomeric a1 GlyR.[47] Briefly, a1 GlyR-HEK293 cells were split
into poly-d-lysine-coated 96-well black Opti-plates (Packard). 16 24 h
later, the medium was aspirated, and 100 mL KREBS Buffer [140 mm
NaCl/4.7 mm KCl/2.5 mm CaCl2/1.2 mm MgCl2/10 mm HEPES/11 mm d-
glucose, pH 7.4] supplemented with FLIPR Membrane Potential Assay
loading dye and various concentrations of the test compounds was added
to the wells. The plate was incubated at 378C in a humidified 5% CO2 in-
cubator for 30 min and assayed in a NOVOstar (BMG Labtechnologies,
Offenburg, Germany) measuring emission at 560 nm caused by excitation
at 530 nm. Fluorescence measurements were performed immediately
before and up to 1 min after addition of glycine (final concentration
100mm) to the wells. The experiments were performed in duplicate at
least three times for each compound. Percentage inhibition was calculat-
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Chem. Eur. J. 2004, 10, 1507 1518