Formal synthesis of angiogenesis inhibitor NM-3

Article abstract of DOI:10.1021/jo034165c

We report the formal synthesis of angiogenesis inhibitor NM-3 (1) in six steps from either of the 2,4-dimethoxyhalobenzenes 13a,b or 3,5-dimethoxychlorobenzene (13c). The first key reaction is the regiospecific alkylation/rearrangement between the aryne derived from 13a-c with sodium diethylmalonate in THF to produce diester 11, which after hydrolysis and cyclization affords homophthalic anhydride 3. The second is the reaction of anhydride 3 with either ethyl 2-methylmalonate (28a), in the presence of 1,1′-carbonyldiimidazole, or ethyl-2-methylmalonyl chloride (28b) under basic conditions to afford key isocoumarin 27. The conversion of 27 constitutes a formal synthesis of NM-3.

Full text of DOI:10.1021/jo034165c

F or m a l Syn th esis of An giogen esis In h ibitor NM-3
William E. Bauta,* Dennis P. Lovett, William R. Cantrell, J r., and Brian D. Burke†
Department of Process Chemistry, Ilex Oncology, Inc., 14785 Omicron Drive, Suite 201,
San Antonio, Texas 78245
wbauta@ilexonc.com
Received February 6, 2003
We report the formal synthesis of angiogenesis inhibitor NM-3 (1) in six steps from either of the
2,4-dimethoxyhalobenzenes 13a ,b or 3,5-dimethoxychlorobenzene (13c). The first key reaction is
the regiospecific alkylation/rearrangement between the aryne derived from 13a -c with sodium
diethylmalonate in THF to produce diester 11, which after hydrolysis and cyclization affords
homophthalic anhydride 3. The second is the reaction of anhydride 3 with either ethyl 2-methyl-
malonate (28a ), in the presence of 1,1′-carbonyldiimidazole, or ethyl-2-methylmalonyl chloride (28b)
under basic conditions to afford key isocoumarin 27. The conversion of 27 constitutes a formal
synthesis of NM-3.
In tr od u ction
The process of angiogenesis, the development and
growth of new vasculature, is involved in a variety of
normal biological functions, as well as disease states
including arthritis, psoriasis, and cancer.1 For this
reason, angiogenesis inhibition has become an active area
of pharmaceutical research, and over 40 such agents are
currently undergoing clinical trials.2 The isocoumarin
NM-3 (1, Figure 1), an analogue of the natural product
cytogenin 2, inhibits the growth of human endothelial
cells in culture and tumor angiogenesis in human tumor
xenograft models.3 Significantly, reductions in mean
tumor volume were observed in animal models when
NM-3 was administered in combination with other
chemotherapeutic agents or radiation, beyond those
observed with chemotherapy or radiotherapy alone.4
NM-3 is currently undergoing Phase I clinical trials.
The patented synthesis of NM-3 by Tsuchida and co-
workers5 involves six steps from dimethyl 1,3-acetonedi-
F IGURE 1.
carboxylate and diketene. Though elegant, this route
suffers from a poor yield in the initial step and the
undesirable expense associated with the use of 1,1′-
carbonyldiimidazole (CDI). A variety of other synthetic
strategies for isocoumarins are known. These include
ortho-metalation approaches,6 palladium-catalyzed cy-
clizations of 2-iodobenzoic acid derivatives,7 Friedel-
Crafts approaches from benzoic acids,8 and ozonolysis of
indanone enol acetates and trifluoroacetates.9 Unfortu-
nately, these approaches would not resolve significant
practical and economic issues for a commercial synthesis
of NM-3.
† Current address: Eli Lilly and Company, Indianapolis, IN.
(1) Carmeliet, P.; J ain R. K. Nature 2000, 407, 249-257. Yanco-
poulos, G. D.; Davis, S.; Gale, N. W.; Rudge, J . S.; Wiegand, S. J .;
Holash, J . Nature 2000, 407, 242-248. Ferrara, N.; Alitalo, K. Nat.
Med. 1999, 5, 1359-1364. Hanahan, D.; Folkman, J . Cell 1996, 86,
353-364. Folkman, J . Breast Cancer Res. Treat. 1995, 36, 181-192.
Folkman, J . J . Natl. Cancer Inst. 1990, 82, 4-6.
Resu lts a n d Discu ssion
As part of our efforts to develop a more efficient process
for NM-3, we investigated the reactions of 3,5-dimethoxy-
homophthalic anhydride (3) with malonate nucleophiles.
Our initial preparation of 3 is shown in Scheme 1. Thus
3,5-dimethoxycinnamic acid (4) was reduced by transfer
hydrogenation to 5 and then cyclized in methanesulfonic
acid to give indanone 6. Acylation of 6 with diethyloxalate
(2) For information on current cancer clinical trials, see: http://
www.cancer.gov/search/clinical_trials/
(3) Oikawa, T.; Sasaki, M.; Inose, M.; Shimamura, M.; Kuboki, H.;
Hirano, S.-I.; Kumagai, H.; Ishizuka, M.; Takeuchi, T. Anticancer Res.
1997, 17, 1881-1886. Nakashima, T.; Hirano, S.-I.; Agata, N.; Kuma-
gai, H.; Isshiki, K.; Yoshioka, T.; Ishizuka, M.; Maeda, K.; Takeuchi,
T. J . Antibiot. 1999, 52, 426-428. Matsumoto, N.; Nakashima, T.;
Isshiki, K.; Kuboki, H.; Hirano, S.-I.; Kumagai, H.; Yoshioka, T.;
Ishizuka, M.; Takeuchi, T. J . Antibiot. 2001, 54, 285-296.
(4) NM-3 with chemotherapy: Reimer, C. L.; Agata, N.; Tamman,
J . G.; Bamberg, M.; Dickerson, W. M.; Kamphaus, G. D.; Rook, S. L.;
Milhollen, M.; Fram, R.; Kalluri, R.; Kufe, D.; Kharbanda, S. Cancer
Res. 2002, 62, 789-795. NM-3 with radiotherapy: Salloum, R. M.;
J askowiak, N. T.; Mauceri, H. J .; Seetharam, S.; Beckett, M. A.; Koons,
A. M.; Hari, D. M.; Gupta, V. K.; Reimer, C.; Kalluri, R.; Posner, M.
C.; Hellman, S.; Kufe, D. W.; Weichselbaum, R. R. Cancer Res. 2000,
60, 6958-6963.
(5) Tsuchida, T.; Nagai, H.; Nakashima, T.; Yoshida, M.; Konuki,
K.; Kuroda, A.; Isshiki, K.; Takeuchi, T. Patent WO 01/07429 A1, 2001.
(6) Watanabe, M.; Sahara, M.; Kubo, M.; Furukawa, S.; Billedeau,
R. J .; Snieckus, V. J . Org. Chem. 1984, 49, 742-747.
(7) Larock, R. C.; Doty, M. J .; Han, X. J . Org. Chem. 1999, 64, 8770-
8779.
(8) Furuta, T.; Fukuyama, Y.; Asakawa, Y. Phytochemistry 1986,
25, 517-520.
(9) Kendall, J . K.; Fisher, T. H.; Schultz, H. P.; Schultz, T. P. J .
Org. Chem. 1989, 54, 4218-4220.
10.1021/jo034165c CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/20/2003
J . Org. Chem. 2003, 68, 5967-5973
5967

Bauta et al.
SCHEME 1 a
SCHEME 2
a
(a) HCO2NH4, 10% Pd/C, EtOH (95% yield); (b) MeSO3H (70%
yield); (c) (i) (EtO2C)2, NaOMe, toluene, (ii) 30% H2O2, KOH,
MeOH (54% yield); (d) Ac2O, toluene, reflux (97% yield).
and subsequent oxidation with alkaline hydrogen per-
oxide, according to Bhakta’s conditions,10 afforded 3,5-
dimethoxyhomophthalic acid (7). Cyclization of 7 to 3 was
accomplished with acetic anhydride in hot toluene,11 and
the product was isolated directly from the reaction as a
white powder.
The high cost of cinnamic acid 4 and concerns of an
uncontrolled exotherm in steps b and c (Scheme 1) led
us to explore an alternative approach to homophthalic
acid 7. The addition of malonate anions to arynes and
their subsequent rearrangement to homophthalate esters
(eq 1), originally reported by Danishefsky,12 was recently
SCHEME 3
employed by Kita and co-workers in their synthesis of
Fredericamycin A.13 Notably, they found that the addition
of dimethyl malonate anion to the aryne derived from
1-bromo-2,3,5-trimethoxybenzene occurred with only mod-
est regioselectivity (3:2).
We reasoned that an aryne of type 8 would react with
diethyl malonate anion to afford intermediate 9 prefer-
entially over 10, owing primarily to the ortho-stabiliza-
tion of the aryl anion by the methoxy group (Scheme 2).14
The resulting homophthalic ester rearrangement product
11 would have the desired regiochemistry to prepare
anhydride 3.
Our preliminary experiments, using conditions ana-
logous to those of Kita and Danishefsky (LiTMP, THF,
-78 °C), gave the desired ester along with a host of
byproducts and dark-colored material that was not fully
characterized. We turned to optimizing the reaction
conditions using the less expensive base lithium diiso-
propylamide (LDA). One prominent byproduct, which we
observed early on, was the N,N-diisopropylaniline 14,
resulting from competitive trapping of the aryne inter-
mediate (Scheme 3).15 We therefore decided on an ap-
proach that would keep the effective concentration of
LDA low at all times: by using a different base to
generate the malonate anion, using only enough LDA as
to generate the aryne intermediate, and adding the LDA
slowly to the reaction mixture. The most useful base for
the generation of the malonate anion was sodium hy-
dride. Sodium amide and lithium hydride were both
unsatisfactory owing to low solubility of either the base
(10) Bhakta, C. Indian J . Chem., Sect. B 1986, 25B, 189-190.
(11) Matstuda, F.; Kawasaki, M.; Ohsaki, M.; Yamada, K.; Terash-
ima, S. Chem. Lett. 1989, 653-656. Matstuda, F.; Kawasaki, M.;
Ohsaki, M.; Yamada, K.; Terashima, S. Tetrahedron 1988, 44, 5745-
5760.
(12) Shair, M. D.; Yoon, T. Y.; Monsy, K. K.; Chou, T. C.; Danishef-
sky, S. J . J . Am. Chem. Soc. 1996, 118, 9509-9525.
(13) Kita, Y.; Higuchi, K.; Yoshida, Y.; Iio, K.; Kitagaki, S.; Ueda,
K.; Akai S.; Fujioka H. J . Am. Chem. Soc. 2001, 123, 3214-3222.
(14) Seconi, G.; Taddei, M.; Eaborn, C.; Stamper, J . G. J . Chem. Soc.,
Perkin Trans. 2 1982, 6, 643-646.
(15) Razzuk, A.; Biehl, E. R. J . Org. Chem. 1987, 52, 2619-2622.
5968 J . Org. Chem., Vol. 68, No. 15, 2003

Formal Synthesis of NM-3
TABLE 1. Com p a r ison of Rea ction P r ofiles for th e
Alk yla tion of 13a -c w ith Dieth yl Ma lon a te
SCHEME 4. P r ep a r a tion of Au th en tic
Hom op h th a la te Ester 12a
crude product mixture
area % (HPLC)
% yield
entry
substrate
12
11
14
isolated 7
1
2
3
13a
13b
13c
0
0
0
82.2
70.0
66.4
7.8
5.0
8.8
39
44
36
or the resultant malonate, respectively, under our reac-
tion conditions.
As the oily homophthalate ester 11 was difficult to
isolate from the excess diethyl malonate, it was con-
venient to saponify the reaction mixture directly and
isolate the corresponding homophthalic acid 7 as a white
solid. Authentic samples of 11 and aniline 14 were
purified by column chromatography for characterization.
Consistent with the aryne mechanism, similar results
were observed for the bromoarene 13a and the isomeric
chloroarenes 13b and 13c (Table 1). Compound 13b,
conveniently prepared by dimethylation of commercially
available 4-chlororesorcinol, was our preferred reagent.
Some specific aspects of our reaction conditions merit
additional comment. Extensive experimentation showed
that addition of LDA over a period of approximately 1 h
to a mixture of the malonate and haloarene at 0-5 °C
obviated the formation of complex mixtures observed at
lower temperatures. Use of minimal LDA was essential
to reducing the quantity of diisopropylaniline byproduct,
as was the use of excess malonate. In practice, 1-1.5
equiv of LDA and 4 equiv of diethylmalonate reproducibly
gave greater than 95% conversion while keeping the
amount of diisopropylaniline 14 to less than 10%. Inter-
estingly, 5.9-6.0 equiv of NaH was required to achieve
greater than 95% conversion. The origin of this effect does
not appear to be related to the NaH purity, which we
tested and found to be consistent with the label claim.
One salient characteristic of these reactions is the
absence of the isomeric homophthalate ester 12. An
authentic sample of 12 was prepared by the route shown
in Scheme 4. Thus, 3,5-dimethoxybenzoic acid (15) was
converted to the corresponding diethylamide 16 using
CDI and diethylamine16 in the presence of acetic acid.
This reaction fails in the absence of acetic acid, possibly
because the more basic amine prevents protonation of
imidazole functions. Amide 16 was then ortho-lithiated
and allylated in the presence of cuprous bromide di-
methyl sulfide complex17 to give 17. Oxidative cleavage
of the terminal olefin to 18, and subsequent hydrolysis
of the amide afforded homophthalic acid 19.18 Conversion
of 19 to the diethyl ester could not be achieved solely by
treatment with thionyl chloride and ethanol, which gave
only the half ester 20, probably because of in situ
formation of the homophthalic anhydride. Esterification
of 20 with CDI and ethanol led to the desired homo-
phthalate 12. The presence of 12 in crude reaction
mixtures from 13a -c and diethylmalonate was not
detected by HPLC.
a
(a) CDI, Et2NH, AcOH, DCE, reflux; (b) (i) s-BuLi, THF, -78
°C, (ii) CuBr‚Me2S, (iii) allyl bromide; (c) RuCl3, NaIO4, CCl4, H2O,
MeCN; (d) 6 N HCl, heat; (e) SOCl2 then EtOH; (f) CDI, CH2Cl2,
EtOH.
SCHEME 5. Rea ction of An h yd r id e 3 w ith a
Dia lk ylm a lon a tes
With an acceptable route to homophthalic anhydride
3, we anticipated that reaction of this material with an
appropriate malonate nucleophile would result in forma-
tion of condensation product 21 (Scheme 5), which, after
monosaponification and decarboxylation, would cyclize
in the presence of acid to the isocoumarin 22. In practice,
we were not able to obtain any isocoumarin product from
such reactions. However, when 3 was reacted with ethyl
malonate (half ester) in the presence of triethylamine,
(16) Rannard, S. P.; Davis, N. J . Org. Lett. 2000, 2, 2117-2120.
(17) Salvadori, P.; Superchi, S.; Minutolo, F. J . Org. Chem. 1996,
61, 4190-4191. Pini, D.; Superchi, S.; Salvadori, P. J . Organomet.
Chem. 1993, C4-C5.
(18) Carlsen, P. H. J .; Katsuki, T.; Martin, V. S.; Sharpless, K. B.
J . Org. Chem. 1981, 46, 3936-3938.
J . Org. Chem, Vol. 68, No. 15, 2003 5969

Bauta et al.
SCHEME 6. P r op osed Mech a n ism for th e
F or m a tion of Isocou m a r in 23
SCHEME 7
study are shown in Scheme 7 and Table 2. Reaction of
the acid 28a with CDI, followed by triethylamine and
anhydride 3, afforded a 66% yield of the desired isocou-
marin 27 (entry 1). Significantly, the ratio of desired
isocoumarin 27 to 23 was 89:11, indicating that the
intermediate acyl imidazole (or ketene) derived from 28a
could compete effectively with the anhydride. When the
acid chloride 28b was reacted under similar conditions,
the ratio was almost opposite that of the CDI reaction,
in favor of isocoumarin 23 (entry 2). We reasoned that
using a stronger base would enolize the anhydride to a
greater extent and thus minimize the chances of self-
condensation, leading to 23. Consistent with this pro-
posal, when anhydride 3 was added to a mixture of acid
chloride 28b and DBU in acetonitrile, only a trace of the
undesired 23 was observed and 27 was isolated in 78%
yield (entry 3). Our initial attempts to use N,N,N′,N′-
tetramethylguanidine (TMG) as a base failed because of
acylation of the base by the malonyl chloride. The
problem was circumvented by adding 3 to a solution of
TMG (1 equiv), followed by addition of triethylamine as
acid scavenger (1 equiv), and finally the malonyl chloride.
By this procedure, there was no detectable 23 formed and
27 was isolated in good yields (entries 4 and 5). Interest-
ingly, the reaction of the mixed anhydride derived from
malonic acid 28a and isobutyl chloroformate (entry 6,
28c) failed to give any 27, producing only 23.
The preparation of 27 constitutes a formal synthesis
of NM-3.5 The final two steps were carried out according
to the reported procedures, and the NM-3 thus produced
was identical to an authentic sample.
In conclusion, we have developed a new synthesis of
NM-3. The regiospecific addition and rearrangement of
diethylmalonate to unsymmetrically substituted aryne
8 at unusually high temperature gave rapid access to
anhydride 3. The remarkably facile reaction of 3 with
activated malonates 28a ,b to afford isocoumarin 27 in
high yield under mild conditions led to an advanced
intermediate in the reported synthesis of NM-3.
the principal product resulted from a self-condensation
reaction between two homophthalic anhydrides. Char-
acterization revealed the structure as isocoumarin 23.
The same product was observed upon reaction of 3 with
Horner-Emmons reagents or with potassium carbonate
and a phase transfer catalyst in THF.
A possible mechanism for the formation of 23 is shown
in Scheme 6. Homophthalic anhydride 3, in the presence
of triethylamine, is assumed to be in equilibrium with
its enolate form 3a . Carbonyl addition by another mol-
ecule of 3 leads to 24, which undergoes transannular
O-acylation to afford 25. Base-promoted ring opening of
25 affords 26. Decarboxylation and olefin isomerization
then result in 23.
Although we were unable to detect the formation of
intermediates 24-26 by HPLC monitoring of the reac-
tion, evidence for the proposed mechanism comes from
the work of Srivastava and co-workers,19 who have
reported that the reaction of homophthalic acids with
anhydrides in pyridine led to benzylic aylation products.
Isocoumarins were obtained if the reaction was carried
out on a steam bath. The similarity of the reactions
suggests that the O-acylation of intermediate 24 (Scheme
6) and the decarboxylation of intermediate 26 are more
facile than in the compounds studied by Srivastava.
The formation of isocoumarin 23 suggested that a
suitably activated malonate might be reacted with ho-
mophthalic anhydride 3, under basic conditions, to
generate an isocoumarin such as 27. The results of this
Exp er im en ta l Section
3-(3,5-Dim eth oxyp h en yl)-p r op ion ic Acid (5). Cinnamic
acid 4 (49.77 g, 239 mmol), 10% Pd/C (2.54 g, 2.39 mmol), and
EtOH (375 mL) were combined, and solid HCO2NH4 (16.58 g,
263 mmol) was added portionwise over 15 min. The mixture
was stirred at ambient temperature for 16 h. The mixture was
filtered through Celite, and the flask and solids were rinsed
with EtOH. The combined filtrate and washes were reduced
(19) Sinha, N. K.; Sahay, L. K.; Prasad, K.; Srivastava, J . N. Ind.
J . Heterocycl. Chem. 1992, 1, 235-240.
5970 J . Org. Chem., Vol. 68, No. 15, 2003

Formal Synthesis of NM-3
TABLE 2. F or m a tion of Isocou m a r in s 27 a n d 23 fr om Hom op h th a lic An h yd r id e 3
entry
malonate
conditions
ratio 27:23
isolated yield, %
1
2
3
4
5
6
28a
28b
28b
28b
28b
28c
CDI, Et3N, MeCN, rt 22 h then reflux 2.5 h
Et3N, MeCN, rt 22 h then reflux 2.5 h
DBU, MeCN, rt
TMG, NMP, Et3N, 0 °C
TMG, MeCN, Et3N, 0 °C
89:11
12:87
99.8:0.2
100:0
100:0
0:100
66
11
78
78
86
0
Et3N, MeCN, rt 17 h then 50 °C 2 h
in vacuo. H2O (250 mL) was added to the residue, and the
resulting suspension was cooled to 0 °C and acidified with 12
M HCl until pH <2. The suspension was filtered, and the flask
and filter cake were washed with H2O. The wet solid was dried
to give 5 as a white powder (47.54 g, 95%), mp 59-61 °C: 1H
NMR (CDCl3) δ 6.38-6.33 (m, 2H), 3.78 (s, 6H), 2.91 (t, 2H, J
) 7.7), 2.68 (t, 2H, J ) 7.7). The spectrum was in agreement
with the reported data.20
5,7-Dim eth oxyin d a n -1-on e (6). Compound 5 (45.02 g,
214.2 mmol) and methane sulfonic acid (MSA, 150.6 g, 1567
mmol) were combined and heated to 95 °C for 6 h. The mixture
was cooled to ambient temperature and poured over crushed
ice. NaOH (50%, 125.4 g, 1567 mmol) was added to neutralize
the MSA. The mixture was extracted with EtOAc (3 × 670
mL), and each organic portion was washed with 5% NaHCO3.
The organic portions were combined, dried (MgSO4), and
reduced in vacuo. The residue was triturated with tert-
butylmethyl ether (TBME, 100 mL), and the resulting suspen-
sion was filtered and dried to give 6 as a tan powder (28.6 g,
70%), mp 99-100 °C: 1H NMR (CDCl3) δ 6.47 (br s, 1H), 6.28
(br s, 1H), 3.90 (s, 3H), 3.86 (s, 3H), 3.03-2.98 (m, 2H), 2.66-
2.61 (m, 2H). The spectrum was in agreement with the
reported data.20
2-Ca r boxym eth yl-4,6-d im eth oxyben zoic Acid (7). A
solution of 6 (36.83 g, 181.8 mmol) and diethyl oxalate (42.03
g, 287.7 mmol) in toluene (400 mL) was added over 45 min to
a suspension of NaOMe (20.21 g, 374.1 mmol) in toluene (20
mL) at 0 °C. After addition was complete, the cooling bath was
removed, and the mixture was stirred for 1 h at ambient
temperature. The solvent was removed in vacuo, and the
residue was suspended in MeOH (1000 mL). Solid KOH (85%,
96.24 g, 1458 mmol) was added portionwise over 45 min,
keeping the temperature below 50 °C. H2O2 (30%, 191 mL,
1870 mmol) was added over 3 h, keeping the temperature
below 64 °C. Gas was evolved during H2O2 addition. After
addition was complete, the mixture was stirred at ambient
temperature for 16 h. The mixture was filtered, and the filtrate
was partially reduced in vacuo to remove MeOH. The remain-
ing aqueous filtrate was washed with TBME, and the organic
layer was discarded. The aqueous layer was acidified with 12
M HCl until pH <2 (∼140 mL). The acidic aqueous layer was
extracted with EtOAc, and the combined organic portions were
dried (MgSO4). The solvent was removed in vacuo, and the
residue was triturated with TBME. The resulting suspension
was filtered and dried to give 7 as a tan powder (25.33 g, 54%),
mp 173-174 °C: 1H NMR (acetone-d6) δ 6.59-6.55 (m, 2H),
3.87 (s, 3H), 3.84 (s, 3H), 3.77 (s, 2H); 13C NMR (acetone-d6) δ
171.7, 168.1, 162.6, 159.9, 137.6, 116.2, 109.3, 97.8, 56.2, 55.6,
39.7. The proton spectrum was in agreement with the reported
data.21
159-162 °C: 1H NMR (CDCl3) δ 6.44 (d, 1H, J ) 2.0), 6.35
(apparent t, 1H, J ) 1.0), 3.98 (s, 2H), 3.94 (s, 3H), 3.89 (s,
3H); 13C NMR (CDCl3) δ 165.8, 165.0, 163.8, 156.8, 138.7,
103.8, 103.2, 98.2, 56.2, 55.8, 35.3. The proton spectrum was
in agreement with the reported data.11
1-Ch lor o-2,4-d im eth oxyben zen e (13b). Sodium hydrox-
ide (50%, 10.8 mL, 204.5 mmol) was added to a solution of
4-chlororesorcinol (10.02 g, 69.29 mmol) in H2O (46 mL)
over 6 min, keeping the temperature below 20 °C. Heptane
(84 mL) was added, followed by dimethyl sulfate (18.1 mL,
191.3 mmol) over 7 min, keeping the temperature below 39
°C. The mixture was stirred at ambient temperature for 16 h.
Stirring was stopped, and the layers were separated. The
aqueous layer was discarded, and the organic layer was
washed with a 3% NH4OH solution and then H2O. The or-
ganic layer was vacuum filtered through silica gel (2.15 g),
and the filtrate was reduced in vacuo to give 13b as a colorless
oil (10.3 g, 86%): 1H NMR (CDCl3) δ 7.23 (d, 1H, J ) 8.7),
6.49 (d, 1H, J ) 2.7), 6.41 (dd, 1 H, J ) 8.7, 2.7), 3.85 (s, 3H),
3.78 (s, 3H); 13C NMR (CDCl3) δ 159.4, 155.5, 130.0, 113.9,
105.0, 99.8, 55.9, 55.4. The spectra were in agreement with
the reported data.22
2-Eth oxyca r bon ylm eth yl-4,6-d im eth oxyben zoic Acid
Eth yl Ester (11). Diethyl malonate (65.81 g, 410.8 mmol) was
added to a mixture of 13b (17.73 g, 102.7 mmol), sodium
hydride (60%, 24.65 g, 616.3 mmol), and THF (190 mL) over
2.4 h, keeping the temperature below 6 °C. LDA (2.0 M, 52
mL, 104 mmol) was added over 2 h, keeping the temperature
below 3 °C. The reaction was quenched into a solution of 12
M HCl (71 mL, 852 mmol) in H2O (200 mL), keeping the
temperature below 21 °C. The layers were separated, and the
aqueous layer was extracted with TBME (95 mL). The aqueous
layer was acidified and extracted to provide a sample of
(3,5-dimethoxyphenyl)-diisopropylamine (14) for analysis: 1H
NMR (CDCl3) δ 6.07 (d, 2H, J ) 2.1), 5.95 (t, 1H, J ) 2.1),
3.78 (septet, 2H, J ) 6.8), 3.77 (s, 6H), 1.25 (d, 12H, J ) 6.8);
13C NMR (CDCl3) δ 160.8, 149.8, 97.0, 89.3, 55.0, 47.5,
21.2; IR (neat, cm-1) 2969, 1612, 1558. Anal. Calcd for
C
14H24ClNO2: C, 61.41; H, 8.84; N, 5.12. Found: C, 61.28; H,
8.60; N, 5.04. The organic portions were combined, and the
solvent was removed in vacuo to give crude 11. A portion of
this material was purified by column chromatography (50%
EtOAc/hexanes) to give pure 11 as a yellow oil: 1H NMR
(CDCl3) δ 6.40 (s, 2H), 4.34 (q, 2H, J ) 7.2), 4.14 (q, 2H, J )
7.2), 3.82 (s, 3H), 3.81 (s, 3H), 3.66 (s, 2H), 1.35 (t, 3H, J )
7.2), 1.24 (t, 3H, J ) 7.2); 13C NMR (CDCl3) δ 170.6, 167.1,
161.4, 158.8, 134.8, 116.2, 107.3, 97.7, 60.8, 55.8, 55.2, 39.5,
14.0 The proton spectrum was in agreement with the reported
data.5
2-Ca r boxym eth yl-4,6-d im eth oxyben zoic Acid (7). The
residue containing crude 11 was dissolved in MeOH (170 mL),
and NaOH (50%, 45 mL, 852.2 mmol) was added over 0.5 h,
keeping the temperature below 46 °C. The resulting suspen-
sion was stirred for 0.5 h and then filtered. The flask and solids
were washed with MeOH. The solid was discarded, and the
filtrate was reduced in vacuo. H2O was added, and the mixture
was heated to reflux for 6 h. The mixture was cooled and
filtered to remove particulates. The filtrate was washed with
TBME, and the organic portion was discarded. After clarifica-
6,8-Dim eth oxy-isoch r om a n -1,3-d ion e (3). Acetic anhy-
dride (4.00 mL, 41.1 mmol) was added via syringe to a slurry
of diacid 7 (8.98 g, 37.4 mmol) in toluene (90 mL), and the
mixture was heated at reflux for 1 h. The flask was cooled in
an ice bath to e2 °C, the solid product was filtered, and the
cake was washed with heptane. The solid was collected and
dried to afford 3 as light yellow crystals (8.04 g, 96.7%), mp
(20) Carter, R. H.; Garson, M. J .; Hill, R. A.; Staunton, J .; Sunter,
D. C. J . Chem. Soc., Perkin Trans. 1 1981, 471-479.
(21) Henderson, G. B.; Hill, R. A. J . Chem. Soc., Perkin Trans. 1
1982, 1111-1115.
(22) Bovicelli, P.; Mincione, E.; Antonioletti, R.; Bernini, R.; Colom-
bari, M. Synth. Commun. 2001, 31, 2955-2963.
J . Org. Chem, Vol. 68, No. 15, 2003 5971

Bauta et al.
tion with charcoal (2.5 g), the aqueous portion was acidified
with 12 M HCl until pH <2 and then extracted with EtOAc.
The organic portion was reduced in vacuo to ∼150 mL, cooled
to 0 °C, stirred for 0.5 h, filtered, and dried to give 7 as a tan
powder (10.93 g, 44%).
vigorously for an additional 4 h. The reaction mixture was
filtered through Celite, and the cake was rinsed with EtOAc.
The phases were separated, the organic layer was washed with
H2O, and the combined aqueous layers were back-extracted
with EtOAc. The combined organic layers were dried (MgSO4),
and the solvent was removed in vacuo to yield crude 18 (0.88
g, 90%). Purification by preparative HPLC (50% H2O/MeCN)
afforded 18 (241 mg, 25%) as a yellow oil: 1H NMR (CDCl3) δ
6.49 (d, 1H, J ) 2.3), 6.34 (d, 1H, J ) 2.3), 3.83 (s, 3H), 3.80
(s, 3H) 3.59 (br m, 1H), 3.31 (q, 3H, J ) 7.1), 1.27 (t, 3H, J )
7.1), 1.13 (t, 3H, J ) 7.1); 13C NMR (CDCl3) δ 171.6, 159.7,
159.5, 159.4, 137.1, 112.9, 101.8, 99.2, 55.7, 55.4, 43.6, 39.7,
34.4, 14.0, 12.6; IR (neat, cm-1) 2975, 1729, 1601, 1463, 1329;
HRMS calcd for C15H21NO5 295.1420, found 295.1418.
2-Car boxym eth yl-3,5-dim eth oxyben zoic Acid (19). Ben-
zamide 18 (129.6 mg, 0.439 mmol) was heated in H2O (2 mL)
and 12 M HCl (2 mL) to reflux for 2.5 h. Upon cooling, a solid
precipitated out of solution. The solid was dissolved in EtOAc,
and the aqueous layer was extracted with EtOAc. The com-
bined organic layers were washed with 1 M HCl and saturated
NaCl and dried (MgSO4), and the solvent was removed in
vacuo to give 19 as a tan solid (85.5 mg, 81%): 1H NMR (10%
CD3OD/CDCl3) δ 7.13 (d, 1H, J ) 2.5), 6.65 (d, 1H, J ) 2.5),
4.03 (s, 2H), 3.84 (s, 3H), 3.83 (s, 3H); 13C NMR (10% CD3OD/
CDCl3) δ 174.8, 169.5, 158.9, 158.8, 131.6, 117.5, 106.0, 102.3,
55.6, 55.2, 31.4; IR (neat, cm-1) 3404, 2924, 2850, 1714, 1604,
1461, 1266, 1204; HRMS calcd for C11H12O6 240.0634, found
240.0634.
N,N-Dieth yl-3,5-d im eth oxyben za m id e (16). CDI (9.79 g,
1.10 mmol) was added in one portion to a solution of acid 15
(10.0 g, 54.9 mmol) in 1,2-dichloroethane (105 mL) Ca u tion :
CO2 is evolved. Diethylamine (6.25 mL, 60.4 mmol) was added
followed by HOAc (3.3 mL, 60.4 mmol). The reaction was
refluxed for 2.25 h. The reaction was cooled to ambient
temperature, additional CDI (8.90 g, 54.9 mmol) was added,
and the mixture was stirred for 16 h at ambient temperature.
An additional amount of diethylamine (5 mL, 48.3 mmol) was
added, and the reaction was warmed to 50 °C and stirred for
22 h. Additional small amounts of CDI and diethylamine were
added over 2 days at 50 °C until a conversion of >97% was
observed by HPLC. The reaction mixture was cooled to
ambient temperature, and 50 mL of 1 M HCl was added to
quench the reaction. The layers were separated, and the
organic layer was washed with 1 M HCl. The combined
aqueous layers were extracted with CH2Cl2. The combined
organic layers were washed with saturated NaHCO3 and then
saturated NaCl. The organic layer was dried (MgSO4), and
solvent was removed in vacuo to afford a dark peach-colored
liquid. The product was purified by silica gel chromatography
(50% EtOAc/heptane) to afford amide 16 as a pale yellow oil
(13.83 g, 56.55 mmol, 103%): 1H NMR (CDCl3) δ 6.47 (m, 3H),
3.78 (s, 6H), 3.45-3.55 (br, 1.5H), 3.40-3.20 (m, 2.5H), 1.25-
1.05 (m, 6H); 13C NMR (CDCl3) δ 170.7, 160.7, 139.0, 110.4,
101.1, 55.3, 43.1, 39.8, 14.1, 12.9; IR (neat, cm-1) 3481, 2971,
1629, 1604. The proton spectrum was in agreement with the
reported data.23 The major contaminate was determined to be
diethylacetamide: 1H NMR (CDCl3) δ 3.38 (q, 2H, J ) 7.1),
3.30 (q, 2H, J ) 7.1), 2.06 (s, 3H), 1.10 (t, 3H, J ) 7.1), 1.08 (t,
3H, J ) 7.1).
2-Eth oxyca r bon ylm eth yl-3,5-d im eth oxyben zoic Acid
(20). Diacid 19 (85.5 mg, 0.356) was dissolved in EtOH
(anhydrous, 200 proof, 5 mL). DMF (1 drop) was charged to
the solution followed by SOCl2 (0.26 mL, 0.356 mmol). The
solvent was removed in vacuo. The crude product was not
purified prior to conversion into diester 12.
2-Eth oxyca r bon ylm eth yl-3,5-d im eth oxyben zoic Acid
Eth yl Ester (12). Crude 20 was dissolved in CH2Cl2 (1 mL),
CDI (65 mg, 0.40 mmol) was charged in a single portion, and
the mixture was stirred for 25 min. EtOH (0.5 mL) was added,
and the mixture was stirred overnight. Additional CDI (32.5
mg, 0.20 mmol) was charged, followed by more EtOH (0.5 mL).
The reaction was stirred for 2 h. The reaction ceased progress-
ing and was worked up. The solvent was removed, and the
residue was dissolved in EtOAc. The organic phase was
washed with 1 M HCl and then with saturated NaCl. The
organic layer was dried (MgSO4), and the solvent was removed
in vacuo. The crude product was purified by preparative TLC
(1/1 EtOAc/Hept + 0.2% AcOH) to give 12 as a tan oil (8.5
mg, 8.1%): 1H NMR (CDCl3) δ 7.07 (d, 1H, J ) 2.5), 6.62 (d,
1H, J ) 2.5), 4.32 (q, 2H, J ) 7.1), 4.14 (q, 2H, J ) 7.1), 4.00
(s 2H), 3.84 (s, 3H), 3.80 (s, 3H), 1.36 (t, 3H, J ) 7.1), 1.24 (t,
3H, J ) 7.1); 13C NMR (CDCl3) δ 172.0, 167.2, 159.0, 158.8,
131.9, 117.5, 105.9, 102.2, 61.0, 60.3, 55.9, 55.4, 31.6, 14.1; IR
(neat, cm-1) 2980, 2942, 1722, 1605, 1464, 1064; MS [M + Na]+
319; HRMS calcd for C15H20O6 296.1260, found 296.1259.
2-(6,8-Dim eth oxy-1-oxo-1H-isoch r om en -3-yl)-p r op ion -
ic Acid Eth yl Ester (27). A solution of anhydride 3 (444.4
mg, 2.00 mmol) in MeCN (12 mL) was added via syringe pump
to a solution of TMG (0.28 mL, 2.20 mmol) in MeCN (5 mL)
over 36 min, maintaining an internal temperature of e0 °C.
Triethylamine (0.56 mL, 4.00) was added in one portion.
Compound 28b (527 mg, 3.20 mmol) was added via syringe
over 3 min, and the mixture was stirred an additional 18 min.
An IPC showed 98.8% conversion by HPLC. The cooling bath
was removed, and the reaction was allowed to warm to
ambient temperature. The reaction mixture was quenched by
addition of 1 M HCl (5 mL). The two phases were separated,
and the organic layer was washed with saturated NaCl and
then dried (Na2SO4) prior to removal of solvent in vacuo to
dryness. The residue was taken into EtOAc (0.5 mL), and the
product was precipitated by addition of heptanes (1.0 mL). The
solid product was filtered and dried to give 27 as a beige solid
(528 mg, 86% yield), mp 109-110 °C: 1H NMR (CDCl3) δ 6.45
2-Allyl-N,N-d iet h yl-3,5-d im et h oxyb en za m id e
(17).
1,10-Phenanthroline (10 mg, used as an indicator) and THF
(20 mL) were combined. The mixture was cooled to -70 °C
under a nitrogen purge. Freshly titrated s-BuLi (0.96 M) was
charged dropwise until a purple/brown color persisted, and
then the full charge of base (10.5 mL, 10.1 mmol) was added.
Amide 16 (2.0 g, 8.43 mmol) was dissolved in THF (10 mL)
and slowly added to the s-BuLi solution over 30 min. Copper-
(I) bromide dimethyl sulfide complex (2.53 g, 12.8 mmol) was
charged in a single portion. The reaction changed from orange
to yellow and was stirred for 5 min. Allyl bromide (0.88 mL,
10.1 mmol) was added over 10 min, and the mixture was
stirred an additional 70 min. The reaction was poured into 1
M HCl. The product was extracted with EtOAc, and the
organic layers were washed with H2O. Insoluble copper salts
formed and were filtered out. The organic layer was separated,
washed with saturated NaCl, and dried (MgSO4), and the
solvent was removed in vacuo to give the crude product as a
brown oil. Attempted purification by silica gel chromatography
(20% EtOAc/heptane) gave crude amide 17 as a light yellow
oil (1.00 g, 43%, 88% auc): 1H NMR (CDCl3) δ 6.43 (d, 1H, J
) 2.3), 6.30 (d, 1H, J ) 2.3), 5.99-5.81 (m, 1H), 5.00 (d, 1H,
J ) 1.8), 4.90 (dd, 1H, J ) 10.1, 2.0), 3.90-3.70 (m, 2H, under
other peaks), 3.80 (s, 3H), 3.78 (s, 3H), 3.27 (d, 2H, J ) 6.36)
3.09 (m, 2H), 1.24 (t, 3H, J ) 7.1), 1.04 (t, 3H, J ) 7.1); IR
(neat, cm-1) 2974, 1632, 1602, 1462, 1432; HRMS calcd for
C
16H23NO3 277.1678, found 277.1680.
(2-Dieth ylca r ba m oyl-4,6-d im eth oxyp h en yl)a cetic Acid
(18). Crude allyl benzamide 17 (920 mg, 3.32 mmol) was
dissolved in MeCN (19.8 mL), H2O (12.6 mL), and CCl4 (12.6
mL). RuCl3‚H2O (68.9 mg, 0.332 mmol) was added to the
stirring solution. NaIO4 (7.09 g, 33.2 mmol) was charged in
three portions over 3.5 h, and the mixture was stirred
(23) Masaguer, C. F.; Ravina, E.; Fontenla, J . A.; Brea, J .; Tristan,
H.; Loza, M. I. Eur. J . Med. Chem. 2000, 35, 83-95.
5972 J . Org. Chem., Vol. 68, No. 15, 2003

Formal Synthesis of NM-3
(d, 1H, J ) 2.3), 6.37 (d, 1H, J ) 2.3), 6.25 (s, 1H), 4.18 (q, 2H,
J ) 7.2), 3.96 (s, 3H), 3.89 (s, 3H), 3.55 (q, 1H, J ) 7.3), 1.51
(d, 3H, J ) 7.3), 1.25 (t, 3H, J ) 7.2); 13C NMR (CDCl3) δ 171.4,
165.3, 163.1, 158.7, 156.1, 141.6, 103.6, 103.1, 100.1, 98.6, 61.3,
56.2, 55.5, 43.6, 15.0, 14.0. The proton spectrum was in
agreement with the reported data.5
NMR (CDCl3) 167.7, 165.3, 163.0, 162.4, 159.6, 159.5, 156.6,
142.2, 140.3, 112.7, 109.0, 104.6, 104.3, 102.8, 99.8, 98.4, 97.8,
56.4, 56.1, 55.5, 37.8; IR (neat, cm-1) 3060, 2943, 1713, 1602;
MS [M - H]- 399.1; HRMS calcd for C21H20O8 400.1158, found
400.1155.
2-(6,8-Dim et h oxy-1-oxo-1H -isoch r om en -3-ylm et h yl)-
4,6-d im eth oxyben zoic Acid (23). Refer to Scheme 7 and
Table 2 for a discussion of this compound, mp 191-193 °C:
1H NMR (CDCl3) δ 6.56 (d, 1H, J ) 2.2), 6.44 (d, 1H, J ) 2.3,
6.36 (d, 1H, J ) 2.2), 6.26 (d, 1H, J ) 2.3), 6.10 (s, 1H), 4.09
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal conditions and analytical data for compounds 3, 5-7, 11,
12, 13b, 14, 16-19, 25, and 27. This material is available free
of charge via the Internet at http://pubs.acs.org.
(s, 1H), 3.91 (s, 3H), 3.90 (s, 3H), 3.82 (s, 3H), 3.81 (s, 1H); 13
C
J O034165C
J . Org. Chem, Vol. 68, No. 15, 2003 5973