Synthesis and biological activity of 4-amino-7-oxo-substituted analogoues of 5-Deaza-5,6,7,8-tetrahydrofolic acid and 5,10-dideaza-5,6,7,8- tetrahydrofolic acid

Article abstract of DOI:10.1021/jm9801298

The 4-amino-7-oxo-substituted analogues of 5-deaza-5,6,7,8- tetrahydrofolic acid (5-DATHF) and 5,10-dideaza-5,6,7,8-tetrahydrofolic acid (DDATHF) were synthesized as potential antifolates. Treatment of the α,β- unsaturated esters 11a-c, obtained in one synthetic step from commercially available para-substituted benzoates (9a-c) and methyl 2-(bromomethly)- acrylate (10), with malononitrile in NaOMe/MeOH afforded the corresponding pyridones 12a-c. Formation of the pyrido[2,3-d]pyrimidines 13a-c was accomplished upon treatment of 12a-c with guanidine in methanol. After the hydrolysis of the ester group present in 13a-c, the resulting carboxylic acids 14a-c were treated with diethyl cyanophosphonate in Et₃N/DMF and coupled with L-glutamic acid dimethyl ester to give 15a-c. Finally, the basic hydrolysis of 15a-c yielded the desired 4-amino-7-oxo-substituted analogues 16a-c in 20-27% overall yield. Compounds 16a-c were tested in vitro against CCRF-CEM leukemia cells. The results obtained indicated that our 4-amino-7- oxo analogues are completely devoid of any activity, the IC₅₀ being higher than 20 μg/mL for all cases except 14c for which a value of 6.7 μg/mL was obtained. These results seem to indicate that 16a-c are inactive precisely due to the presence of the carbonyl group in position C7, the distinctive feature of our synthetic methodology.

Full text of DOI:10.1021/jm9801298

J . Med. Chem. 1998, 41, 3539-3545
3539
Notes
Syn th esis a n d Biologica l Activity of 4-Am in o-7-oxo-Su bstitu ted An a logu es of
5-Dea za -5,6,7,8-tetr a h yd r ofolic Acid a n d 5,10-Did ea za -5,6,7,8-tetr a h yd r ofolic
Acid
J ose´ I. Borrell,* J ordi Teixido´, Blanca Mart´ınez-Teipel, J osep Llu´ıs Matallana, M. Teresa Copete,
Ana Llimargas, and Eva Garc´ıa
Departament de Quı´mica Orga`nica, Institut Quı´mic de Sarria`, Universitat Ramon Llull, Via Augusta 390,
E-08017 Barcelona, Spain
Received February 27, 1998
The 4-amino-7-oxo-substituted analogues of 5-deaza-5,6,7,8-tetrahydrofolic acid (5-DATHF) and
5,10-dideaza-5,6,7,8-tetrahydrofolic acid (DDATHF) were synthesized as potential antifolates.
Treatment of the R,â-unsaturated esters 11a -c, obtained in one synthetic step from com-
mercially available para-substituted methyl benzoates (9a -c) and methyl 2-(bromomethyl)-
acrylate (10), with malononitrile in NaOMe/MeOH afforded the corresponding pyridones 12a -
c. Formation of the pyrido[2,3-d]pyrimidines 13a -c was accomplished upon treatment of
12a -c with guanidine in methanol. After the hydrolysis of the ester group present in 13a -c,
the resulting carboxylic acids 14a -c were treated with diethyl cyanophosphonate in Et3N/
DMF and coupled with L-glutamic acid dimethyl ester to give 15a -c. Finally, the basic
hydrolysis of 15a -c yielded the desired 4-amino-7-oxo-substituted analogues 16a -c in 20-
27% overall yield. Compounds 16a -c were tested in vitro against CCRF-CEM leukemia cells.
The results obtained indicated that our 4-amino-7-oxo analogues are completely devoid of any
activity, the IC50 being higher than 20 µg/mL for all cases except 14c for which a value of 6.7
µg/mL was obtained. These results seem to indicate that 16a -c are inactive precisely due to
the presence of the carbonyl group in position C7, the distinctive feature of our synthetic
methodology.
In tr od u ction
Chemotherapeutic agents that act on DNA synthesis
have been widely used in the treatment of cancer.
Nearly all types of cells can synthesize the necessary
nucleotides de novo or from the degradation products
of nucleic acids. While the de novo synthetic route is
almost the same in all kinds of cells, recovery pathways
are quite different in characteristics and distribution.
The fact that cancer cells are dependent on the de novo
synthesis of purines more than normal cells allows an
anticancer agent which acts on this pathway, while
leaving the recovery pathway unaltered, to have a
certain degree of selectivity and, consequently, lower
toxicity.1
F igu r e 1.
Folic acid (FA, 1) and derivatives, especially 5,6,7,8-
tetrahydrofolic acid (H4FA), participate as coenzymes
in the transference, oxidation, and reduction of carbon
units in numerous biochemical routes (Figure 1).2 Thus,
acting on folic acid metabolism provides a way to
intervene in the de novo biosynthesis of nucleotides.
This objective has been sought by several different
approaches.
A traditional approach is the inhibition of dihydro-
folate reductase (DHFR), the enzyme which catalyzes
the transformation of 7,8-dihydrofolic acid (H2FA) to H4-
FA. The synthesis of potent DHFR inhibitors (Figure
2) such as aminopterin (AMT, 2) and methotrexate
(MTX, 3),3 currently widely used for cancer chemo-
therapy, has brought about the development of a large
series of analogues.4,5
More recently, a new mechanism of action was found
in the case of 5-deaza-5,6,7,8-tetrahydrofolic acid (5-
DATHF, 4) and 5,10-dideaza-5,6,7,8-tetrahydrofolic acid
(DDATHF, 5) synthesized by E. C. Taylor et al. (Figure
2).6,7 These compounds inhibit glycinamide ribonucle-
otide transformylase (GARTFase), responsible for the
transformation of glycinamide ribonucleotide (GAR) into
R-N-formylglycinamide ribonucleotide (FGAR), therefore
inhibiting the biosynthesis of purines. The 6R-diaste-
S0022-2623(98)00129-0 CCC: $15.00 © 1998 American Chemical Society
Published on Web 08/01/1998

3540 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 18
Notes
1, led to the R,â-unsaturated esters 11a -c, which were
further disconnected to a nucleophilic para-substituted
methyl benzoate 9a -c and methyl 2-(bromomethyl)-
acrylate (10). Although commercially available, this
was obtained in a 67% yield over two steps by following
the method of J . Villieras and M. Rambaud16 starting
from trimethyl phosphonoacetate. Then, the treatment
of 10 with methyl 4-methylaminobenzoate (9a ) in
methanol afforded methyl p-[N-(2-methoxycarbonylal-
lyl)-N-methylamino]benzoate (11a) in 99% yield (Scheme
2). Similarly, methyl p-[N-(2-methoxycarbonylallyl)-
amino]benzoate (11b) was obtained in 74% yield by
reaction of methyl 2-(bromomethyl)acrylate (10) and
methyl 4-aminobenzoate (9b) in the presence of Et3N
in toluene.
F igu r e 2.
Finally, the synthesis of methyl p-(3-methoxycarbo-
nyl-3-butenyl)benzoate (11c) was achieved by using a
metal-catalyzed cross coupling reaction according to the
methodology described by P. Knochel et al.17,18 Thus,
the organometallic derivative 9c was formed by the slow
addition of methyl p-bromomethylbenzoate, obtained by
methylation of p-bromomethylbenzoic acid with diazo-
methane, to a suspension of activated zinc in anhydrous
THF at 0 °C in an inert atmosphere. The resulting
mixture was added to a solution of CuCN and LiCl in
THF at -78 °C, the transmetalation being ensured by
warming the solution to -20 °C for 5 min. After the
solution was cooled to -78 °C, methyl 2-(bromomethyl)-
acrylate (10) was added to the mixture of 9c in THF to
afford 11c. The yield obtained was found to be depend-
ent on the rate of addition of the methyl p-bromometh-
ylbenzoate to the zinc suspension. Table 1 summarizes
the yields of 11c and the two byproducts obtained, 17
and 18, as a function of the rate of addition of methyl
p-bromomethylbenzoate.
Formation of 18 can be explained by a Wurtz-type
coupling of the Zn organometallic intermediate. This
kind of reaction is frequent in benzylic or allylic
bromides, with 18 even being the only product isolated.19
The amount of 18 could be minimized by a careful
control of the rate of addition of the methyl p-bromo-
methylbenzoate, which must be approximately a drop
every 5 s.20
As for the formation of 17, it can only be explained
by the presence of water in the medium that destroys
either the Zn or the Cu organometallic. To minimize
the amount of 17 formed (expt 4), it was necessary to
dry the glassware in an oven, to use THF freshly
distilled over LiAlH4, and to dry the LiCl over P2O5 at
60 °C under reduced pressure for 24 h.
F igu r e 3.
Sch em e 1
reomer of DDATHF (lometrexol), in which the H-C6
atom has the same spatial orientation as in H4FA, has
recently finished phase II clinical trials.8,9
Usually these folic acid analogues are synthesized
through a strategy employing the reaction of a conve-
niently substituted benzoate and a preformed bicyclic
heterocyclic compound, normally obtained by cyclization
of adequate substituents present in a pyrimidine ring.
During the past few years, our group has developed
an alternative strategy for the formation of 5,6,7,8-
tetrahydropyrido[2,3-d]pyrimidin-7-ones of general struc-
ture 8 (Scheme 1) by cyclization with guanidine of
2-methoxy-6-oxo-1,4,5,6-tetrahydropyridine-3-carboni-
triles (7), obtained by reaction of an R,â-unsaturated
ester 6 and malononitrile in NaOMe/MeOH.10-15
A structural comparison (Figure 3) between 8 and the
antifolates 5-DATHF (4) and DDATHF (5) showed that,
if it were possible to introduce the long side chain
present on C6 of the inhibitors, new analogues with
potential activity could be obtained, the main difference
being the presence of a carbonyl group at C7 and an
amino group at C4.
The quality and activation of the zinc employed was
also critical for the progress of the reaction. In the
present work, we used Zn from Fluka (art. 96453,
puriss., grit, g99.5%), which was cleaned with diluted
HCl and activated with 1,2-dibromoethane in boiling
THF. A coupling reaction carried out with Zn dust did
not afford the desired product.
In the optimal experimental conditions found (expt
4), methyl p-(3-methoxycarbonyl-3-butenyl)benzoate (11c)
was obtained in a 77% yield.
Now, we report the use of our methodology for the
synthesis of 16a -c (Scheme 2), 4-amino-7-oxo-substi-
tuted analogues of 5-DATHF (4) and DDATHF (5), and
the determination of their biological activity.
The syntheses of the 2-methoxy-6-oxo-1,4,5,6-tetrahy-
dropyridine-3-carbonitriles 12a -c were carried out by
following the general method developed by our group
(Scheme 1) which has been tested with a wide range of
Resu lts a n d Discu ssion
Ch em istr y. A retrosynthetic analysis of structures
16a-c, according to the methodology depicted in Scheme

Notes
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 18 3541
Sch em e 2
Ta ble 1. Yields of 11c and the Two Byproducts Obtained, 17
and 18, as a Function of the Rate of Addition of Methyl
p-Bromomethylbenzoate to the Zinc Suspension
Our initial strategy for the syntheses of the folic acid
analogues 15a -c was to activate the carboxylic acids
14a -c by using 2-chloro-4,6-dimethoxy-1,3,5-triazine
(19) in the presence of N-methylmorpholine (NMM, 20)
and to react the resulting ester with L-glutamic acid
dimethyl ester, following the method described by Z.
Kaminski.24 This reagent has been widely used in the
formation of folic acid analogues and, in particular, was
employed by E. C. Taylor in the synthesis of DDATHF.
However, the treatment of 14a or 14b in the afore-
mentioned reaction conditions did not yield the corre-
sponding amides 15a ,b, either at room temperature or
at 70 °C, the starting acids being recovered and a
byproduct being formed. This compound was identified
as the 2,4-dimethoxy-6-(N-morpholin)-1,3,5-triazine (22).
Formation of 22 could be rationalized as follows: the
low solubility of the starting acids 14a ,b in DMF
precludes the ionization of the carboxylic acid by the
NMM, and then the 2-chloro-4,6-dimethoxy-1,3,5-tri-
azine (19) undergoes the nucleophilic substitution of the
chlorine atom by the NMM with formation of the
quaternary ammonium salt 21, which finally reverts to
22 during the evaporation of the DMF (80 °C at 2-4
mmHg) due to the demethylation of 21 caused by the
chloride ion.
However, when we used triazine 19 for the coupling
of the also poorly soluble 14c, we obtained the desired
15c in 58% yield. This result led us to think that the
low solubility is not the only factor which favors the
formation of 22. So we decided to test the coupling of
L-glutamic acid dimethyl ester with p-toluic acid and
p-methylaminobenzoic acid using the 2-chloro-4,6-
dimethoxy-1,3,5-triazine (19) and NMM. In the first
case, we obtained the coupled product in 75% yield, but
in the second one, 22 was obtained as the predominant
product. Therefore, the use of 19 and NMM for the
coupling of folic acid analogues which contain a nitrogen
atom in the CH2X bridge should not be recommended.
rate of
entry
add.a (g/h)
11c (%)
17 (%)
18 (%)
expt 1
expt 2
expt 3
expt 4b
3.7
0.9
2.9
2.5
16
28
55
77
24
16
21
2
14
5
3
0.5
a
Rate of addition of methyl p-bromomethylbenzoate to the zinc
suspension. LiCl was dried over P2O5 at 60 °C under reduced
pressure for 24 h.
b
R,â-unsaturated esters.21 The yields obtained depend
on the nature and position of the substituents present
in the ester. In particular, yields are lower in 2-sub-
stituted acrylates due to formation of the Michael
bisadduct as a byproduct. Thus, in the case of methyl
methacrylate, it was necessary to apply a simplex
optimization method to find the optimal reaction condi-
tions.22 Similarly, 11a -c underwent Michael addition
followed by cyclization when treated with malononitrile
in NaOMe/MeOH to afford pyridones 12a -c in 40-55%
yield (Scheme 2). Compounds 12a -c were obtained as
racemic mixtures and used without separation. How-
ever, enantioresolution of 12a and 12c is possible by
using reversed phase HPLC on a vancomycin chiral
stationary phase (CHIROBIOTIC V) column from Ad-
vanced Separation Technologies (Whippany, NJ ), em-
ploying a mixture of 90% buffer solution (1% triethyl-
ammonium acetate) and 10% acetonitrile as eluent.23
Next, the 2,4-diaminopyrido[2,3-d]pyrimidines 13a -c
were obtained in 80-95% yield by treatment of the
corresponding compounds 12a -c with 2 equiv of guani-
dine in MeOH at reflux for 20 h. The syntheses of
13a -c prove again the general applicability of the
methodology depicted in Scheme 1. Subsequently,
compounds 13a -c were hydrolyzed in 1 N aqueous
NaOH to afford the corresponding carboxylic acids in
almost quantitative yield.
This unexpected problem led us to change the activat-
ing agent, and we shifted to diethyl cyanophosphonate
which has successfully been used in the coupling of
L-glutamic acid dimethyl ester with pyrrolo[2,3-d]pyri-
midines25 and other nitrogenated compounds.26 Thus,
the treatment of the acids 14a -c with diethyl cyano-
phosphonate in DMF using Et3N as the base, followed
by addition of L-glutamic acid dimethyl ester, gave the
corresponding coupled products 15a -c in 70-85% yield.

3542 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 18
Notes
Ta ble 2. Structures and in Vitro Cytotoxicity Assay (IC50
Conducted in CCRF-CEM Human Leukemia Cells
)
feature of our synthetic methodology. The only remain-
ing question is if such negative effect of the carbonyl
group would be also present in 7-oxo-substituted ana-
logues of DDATHF which would be targeted against
glycinamide ribonucleotide transformylase (GARTFase).
Experiments are being conducted to clarify this point.
Exp er im en ta l Section
All melting points, determined with a Bu¨chi 530 capillary
apparatus, and boiling points, determined during distillation,
are uncorrected. Infrared spectra were recorded in a BOMEM
Michelson 100 and a Nicolet Magna 560 FTIR spectrophotom-
eters. UV spectra were registered in a Hewlett-Packard 8450
instrument. 1H and 13C NMR spectra were determined in a
Varian Gemini-300 operating at a field strength of 300 and
75.5 MHz, respectively. Chemical shifts are reported in parts
per million (δ) and coupling constants (J ) in Hz using, in the
case of 1H NMR, TMS or sodium 2,2,3,3-tetradeuteriotri-
methylsilylpropionate as an internal standard and setting, in
the case of 13C NMR, the references at the signal of the
solvent: 77.0 ppm (CDCl3); 39.5 ppm (DMSO-d6); 163.8 ppm
(CF3COOD, TFA-d). Standard and peak multiplicities are
designated as follows: s, singlet; d, doublet; dd, doublet of
doublets; t, triplet; brs, broad singlet; br, broad signal; m,
multiplet. Mass spectra (m/z (%), EI, 70 eV) were obtained
on a Hewlett-Packard 5995 A spectrometer. FAB(+)-HRMS
were registered at the Servicio de Espectrometr´ıa de Masas
(Universidad de Co´rdoba) using a VG Autospec spectrometer
(resolution 8000, 3-nitrobenzyl alcohol as matrix). Elemental
microanalyses were obtained on a Carlo-Erba CHNS-O/EA
1108 analyzer and gave results for the elements stated with
(0.4% of the theoretical values. N,N-Dimethylformamide
(DMF) was dried over activated (250 °C) 4-Å molecular sieves.
Tetrahydrofuran (THF) was distilled from LiAlH4 and kept
over 4-Å molecular sieves. MeOH refers to methanol, Et2O
refers to diethyl ether, AcOEt refers to ethyl acetate, and
Carbitol refers to 2-(2-ethoxyethoxy)ethanol. Thin layer chro-
matographies (TLC) were performed on precoated sheets of
silica 60 Polygram SIL N-HR/UV254 (Macherey Nagel art.
804023). Dry-column chromatography was performed using
silica gel 70-230 mesh (ASTM) (Merck art. 7734 or Macherey
Nagel art. 81533). Flash chromatography was performed
using silica gel 230-400 mesh (ASTM) (Macherey Nagel art.
81538). Diazomethane in Et2O was prepared starting from
diazald (N-methyl-N-nitroso-p-toluenesulfonamide) by using
the method and apparatus described by M. Hudlicky.29
Meth yl 2-(Br om om eth yl)a cr yla te (10).16 A saturated
aqueous solution of 33.81 g (0.24 mol) potassium carbonate
was slowly added (30 min) to a mixture of 25.86 g (0.15 mol)
of trimethyl phosphonoacetate and 50.50 g (0.59 mol) of a 35%
aqueous solution of formaldehyde stirred at room temperature.
At the end of the addition, the temperature rose to 30-35 °C,
and stirring was maintained for 1 h. Then, a saturated
solution of ammonium chloride (150 mL) was added, and the
resulting mixture was extracted with CH2Cl2 (3 × 50 mL). The
organic extracts were dried (MgSO4) and concentrated to give
16.24 g (0.14 mol, 89%) of methyl 2-(hydroxymethyl)acrylate
as a colorless liquid which was used without any further
purification. To a stirred solution of 13.60 g (0.12 mol) of
methyl 2-(hydroxymethyl)acrylate in 250 mL of Et2O was
added 14.60 g (0.054 mol) of phosphorus tribromide at -20
°C. The resulting mixture was heated to room temperature
and maintained with stirring for 3 h. Then it was cooled to
-20 °C, and 150 mL of water were added. The mixture was
extracted with hexane (3 × 50 mL), dried (MgSO4), and
concentrated in vacuo to give 13.36 g (0.091 mol, 78%) of 10
which was used without any further purification.
compd
X
Y
IC50 (µg/mL)
13a
13b
13c
14a
14b
14c
16a
16b
16c
NMe
NH
CH2
NMe
NH
CH2
NMe
NH
OMe
OMe
OMe
OH
>20
>20
>20
>20
>20
OH
OH
6.7
Glua
Glu
>20
>20
CH2
Glu
39.2
a
Glu ) HO2CCH2CH2CH(CO2H)NH-.
The last step for the syntheses of the folic acid
analogues 16a -c is the basic hydrolysis of the ester
groups present in the glutamate unit. Hydrolyses
carried out using 1 N NaOH at room temperature
during 24 h afforded the corresponding compounds
16a -c in 85-95% yield.
To sum up, compounds 16a-c, which are the 4-amino-
7-oxo-substituted analogues of5-DATHF (4)and DDATHF
(5), have been obtained in 6 steps, from commercially
available compounds, in 25, 19, and 27% total yields,
respectively.
Biologica l Eva lu a tion . Compounds 13a -c, 14a -
c, and 16a -c were tested in vitro against CCRF-CEM
leukemia cells (Table 2).27 This is a very common T cell
derived lymphoblastic leukemia that has been widely
used as a discriminatory test. Both DDATHF (5) and
methotrexate (3) demonstrated potent growth inhibitory
activity against the CCRF-CEM cells, the IC50 of
DDATHF and methotrexate being 0.007 µg/mL and
0.004 µg/mL, respectively.
The results obtained indicated that our 4-amino-7-
oxo analogues are completely devoid of any activity, the
IC50 being higher than 20 µg/mL for all cases except 14c
for which a value of 6.7 µg/mL was obtained. This lack
of activity cannot be attributed to the low solubility of
these compounds in aqueous system because, in the test
performed, all the compounds are dissolved in DMSO
and then diluted into aqueous buffer solution to the
desired concentration. Both DDATHF and methotrex-
ate are not very soluble even under these conditions,
yet they are very potent and cytotoxic compounds.
Compounds 16a -c present a 2,4-diaminopyrimidine
ring and thus are primarily targeted at DHFR, and it
is known that oxygenation at the 7 position is, in
general, not good for DHFR binding. Thus, for instance,
methotrexate inhibited rat liver DHFR with an IC50 of
23 nM, whereas the corresponding value for 7-hy-
droxymethotrexate was 4000 nM.28
Consequently, taking into account that the 4-amino-
substituted analogue of DDATHF was able to inhibit
bovine liver DHFR with an IC50 of 71 nM,7 it has to be
concluded that our 4-amino-7-oxo-substituted analogues
of DDATHF are inactive precisely due to the presence
of the carbonyl group in position C7, the distinctive
Meth yl p-[N-(2-Meth oxyca r bon yla llyl)-N-m eth yla m i-
n o]ben zoa te (11a ). A solution of 10.80 g (0.06 mol) of methyl
2-(bromomethyl)acrylate (10) in 20 mL of MeOH was added
to a suspension of 10.00 g (0.06 mol) of methyl 4-methylami-
nobenzoate (9a ) in 30 mL of MeOH. The resulting mixture
was stirred for 12 h at room temperature. Then the solvent

Notes
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 18 3543
was removed at reduced pressure, and the residue was
suspended in water. The mixture was neutralized (pH ) 7-8)
with a saturated solution of NaHCO3 and extracted with CH2-
Cl2 (5 × 50 mL). The combined extracts were dried (MgSO4)
and concentrated in vacuo to give 16.90 g (0.06 mol, 99%) of
11a as a yellow solid: mp 40-42 °C; IR (CHCl3), 3000, 1715
(CdO), 1610, 1525, 770 cm-1; UV (MeOH) λmax (log ꢀ) 202
(2.600), 306 (2.678) nm; MS m/z 263 (60) [M+], 232 (40), 204
(40), 178 (100). Anal. (C14H17NO4) C, H, N.
(pH ) 8) with a 3% HCl solution. The solid formed was
filtered, washed with cool water, and dissolved in CH2Cl2. The
aqueous layer formed was extracted with CH2Cl2 (2 × 50 mL).
The combined organic extracts were washed with water, dried
(MgSO4), and concentrated to give 2.62 g (8.0 mmol, 55%) of
12a as a colorless solid: mp 177-178 °C; IR (KBr) 3210, 3110
(N-H), 2200 (CN), 1715 (COOMe), 1690 (CONH), 1640, 1615
(CdC), 770 cm-1; UV (MeOH) λmax (log ꢀ) 309.0 (3.158); MS
m/z 329 (29) [M+], 298 (12), 178 (100). Anal. (C17H19N3O4) C,
H, N.
Meth yl p-[N-(2-Meth oxyca r bon yla llyl)a m in o]ben zoa te
(11b). A solution of 3.00 g (0.017 mol) of methyl 2-(bromo-
methyl)acrylate (10) in 10 mL of toluene was added to a
suspension of 2.53 g (0.017 mol) of methyl 4-aminobenzoate
(9b) and 1.69 g (0.017 mol) of Et3N in 20 mL of toluene. The
resulting mixture was stirred for 96 h at room temperature.
Then the mixture was filtered to separate the triethylammo-
nium bromide formed and was concentrated in vacuo. The
solid obtained was column chromatographed using AcOEt/
hexane (1:2) as eluent to give 2.61 g (0.01 mol, 74%) of 11b as
a yellow solid: mp 63-65 °C; IR (film), 3330 (N-H), 1700 (Cd
O), 1610, 1525, 770 cm-1; UV (MeOH) λmax (log ꢀ) 202 (2.334),
301 (2.381) nm; MS m/z 249 (99) [M+], 218 (59), 164 (100), 158
(42), 130 (65). Anal. (C13H15NO4) C, H, N.
Meth yl p-[N-(5-Cya n o-6-m eth oxy-3,4-d ih yd r o-2-p yr i-
d on -3-ylm eth yl)a m in o]ben zoa te (12b). The procedure was
the same as that stated above for 12a but using 3.00 g (12
mmol) of methyl p-[N-(2-methoxycarbonylallyl)amino]benzoate
(11b) in 6 mL of MeOH, 0.41 g (18 mmol) of Na in 12 mL of
MeOH, 0.95 g (14 mmol) of malononitrile in 6 mL of MeOH,
and refluxed for 2 h. Neutralization was accomplished with
25% acetic acid. The yield was 1.62 g (5 mmol, 43%) of 12b
as a colorless solid: mp 181-183 °C; IR (KBr) 3400 (N-H),
3200, 3100 (CON-H), 2200 (CN), 1700 (COOMe), 1690 (CONH),
1640, 1605 (CdC), 770 cm-1; UV (MeOH) λmax (log ꢀ) 313.3
(2.413); MS m/z 315 (10) [M+], 284 (4), 164 (100), 151 (47).
Anal. (C16H17N3O4) C, H, N.
Meth yl p-(3-Meth oxycar bon yl-3-bu ten yl)ben zoate (11c).
A suspension of 5.00 g (23 mmol) of p-bromomethylbenzoic acid
(Fluka art. 18520) in 100 mL of Et2O was treated with an
ethereal solution of diazomethane29 (5.35 g (25 mmol) of
diazald in 250 mL of Et2O and 1.50 g (27 mmol) of KOH in 25
mL of EtOH). The resulting solution was stirred for 12 h,
extracted with a 10% NaHCO3 solution, dried (MgSO4), and
concentrated in vacuo to give 5.22 g (23 mmol, 98%) of 9c as
a colorless solid: mp 52-55 °C. A mixture of 3.63 g (56 mmol)
of Zn (obtained by washing 4.00 g of Zn, Fluka art. 96453,
puriss., grit, g 99.5%, with 10% aqueous HCl for 2 min and
then rinsing with water and acetone), 10 mL of anhydrous
THF, and a few drops of 1,2-dibromoethane was heated at
reflux for 5 min in an inert atmosphere. After the solution
was cooled, a solution of 10.51 g (46 mmol) of 9c in 20 mL of
anhydrous THF was added dropwise at 0 °C during 4 h by
using a peristaltic pump (Pharmacia Biotech peristaltic pump
P-1). After being stirred for 2-3 h at 0 °C, the resulting
solution was added by using the aforementioned peristaltic
pump to a suspension of 4.11 g (46 mmol) of CuCN and 3.89
g (92 mmol) of LiCl (dried over P2O5 at 60 °C under reduced
pressure for 24 h) in 100 mL of anhydrous THF cooled to -78
°C in an inert atmosphere. The resulting mixture was warmed
to -20 °C for 5 min and cooled again to -78 °C. Then, a
solution of 9.15 g (50 mmol) of methyl 2-(bromomethyl)acrylate
(10) in 50 mL of anhydrous THF was added dropwise. The
mixture was warmed to 0 °C and stirred for 12 h. Then it
was poured into a mixture of CH2Cl2 and a saturated solution
of ammonium chloride, stirred, and filtered to separate the
inorganic salts formed. The two layers were separated, and
the aqueous layer was extracted with CH2Cl2 (3 × 50 mL).
The combined organic extracts were washed with water and
with brine, dried (MgSO4), and concentrated in vacuo. The
crude material was purified by flash chromatography using
AcOEt/hexane (1:10) as eluent to give 8.76 g (35 mmol, 77%)
of 11c as a colorless oil which crystallizes on standing: mp
Meth yl p-[2-(5-Cyan o-6-m eth oxy-3,4-dih ydr o-2-pyr idon -
3-yl)eth yl]ben zoa te (12c). The procedure was the same as
that stated above for 12a but using 6.71 g (27 mmol) of methyl
p-(3-methoxycarbonyl-3-butenyl)benzoate (11c) in 15 mL of
MeOH, 0.93 g (41 mmol) of Na in 20 mL of MeOH, 2.14 g (32
mmol) of malononitrile in 15 mL of MeOH, and refluxed for
2.5 h. Neutralization was accomplished with 3% HCl. The
yield was 4.37 g (14 mmol, 51%) of 12c as a colorless solid:
mp 146-147 °C; IR (KBr) 3205, 3105 (N-H), 2200 (CN), 1720
(COOMe), 1695 (CONH), 1640, 1610 (CdC), 770 cm-1; MS m/z
314 (20) [M+], 283 (17), 152 (100). Anal. (C17H18N2O4) C, H,
N.
Gen er a l Meth od for th e Syn th eses of 2,4-Dia m in o-7-
oxo-5,6,7,8-tetr ah ydr opyr ido[2,3-d]pyr im idin es 13. Meth -
yl p-[N-(2,4-Dia m in o-7-oxo-5,6,7,8-tetr a h yd r op yr id o[2,3-
d ]p yr im id in -6-ylm eth yl)-N-m eth yla m in o]ben zoa te (13a ).
A 0.79-g (4-mmol) portion of guanidine carbonate was added
to a solution of 0.20 g (9 mmol) of Na in 25 mL of MeOH, and
the mixture was refluxed for 15 min. After the solution was
cooled, the sodium carbonate formed was filtered, and 1.35 g
(4 mmol) of methyl p-[N-(5-cyano-6-methoxy-3,4-dihydro-2-
pyridon-3-ylmethyl)-N-methylamino]benzoate (12a) was added.
The mixture was heated at reflux for 20 h and cooled to room
temperature. The solid was filtered, washed with MeOH and
Et2O, and dried over P2O5 to give 1.18 g (3 mmol, 83%) of 13a
as a colorless solid: mp 282 °C; IR (KBr) 3600, 3440, 3340,
3210, 3060 (N-H), 1685 (COOMe), 1660 (CONH), 1610, 1570
(CdC, CdN), 770 cm-1; MS m/z 356 (15) [M+], 325 (8), 178
(100). Anal. (C17H20N6O3‚H2O) C, H, N.
Meth yl p-[N-(2,4-Dia m in o-7-oxo-5,6,7,8-tetr a h yd r op y-
r id o[2,3-d ]p yr im id in -6-ylm eth yl)a m in o]ben zoa te (13b).
The procedure was the same as that stated above for 13a but
using 0.074 g (3.2 mmol) of Na in 6 mL of MeOH, 1.03 g (1.76
mmol) of guanidine carbonate, and 0.5 g (1.6 mmol) of methyl
p-[N-(5-cyano-6-methoxy-3,4-dihydro-2-pyridon-3-ylmethyl)-
amino]benzoate (12b). The yield was 0.48 g (1.4 mmol, 88%)
of 13b as a colorless solid: mp 275-278 °C; IR (KBr) 3470,
3380, 3220, 3100 (N-H), 1690 (CdO), 1630, 1610, 1570 (Cd
C, CdN), 765 cm-1; MS m/z 342 (15) [M+], 191 (74), 178 (33),
120 (100). Anal. (C16H18N6O3) C, H, N.
39-41 °C; IR (film) 3000, 1720 (CdO), 1630, 1610, 770 cm-1
;
MS m/z 248 (0.6) [M+], 217 (1.7), 149 (100). Anal. (C14H16O4)
C, H.
Gen er a l Meth od for th e Syn th eses of P yr id on es 12.
Meth yl p-[N-(5-Cya n o-6-m eth oxy-3,4-d ih yd r o-2-p yr id on -
3-ylm eth yl)-N-m eth yla m in o]ben zoa te (12a ). A solution of
1.16 g (15.5 mmol) of malononitrile in 7 mL of MeOH was
added all at once to a solution of 0.49 g (21.2 mmol) of Na in
13 mL of MeOH in an inert atmosphere. After this solution
was stirred for a few minutes, a solution of 3.85 g (14.6 mmol)
of methyl p-[N-(2-methoxycarbonylallyl)-N-methylamino]ben-
zoate (11a ) in 7 mL of MeOH was added dropwise. The
mixture was heated at reflux for 3 h and, after being cooled,
was concentrated in vacuo. The residue obtained was dis-
solved in water, cooled in an ice bath, and carefully neutralized
Meth yl p-[2-(2,4-Dia m in o-7-oxo-5,6,7,8-tetr a h yd r op y-
r id o[2,3-d ]p yr im id in -6-yl)eth yl]ben zoa te (13c). The pro-
cedure was the same as that stated above for 13a but using
0.17 g (7.4 mmol) of Na in 20 mL of MeOH, 0.66 g (3.7 mmol)
of guanidine carbonate, and 1.16 g (3.7 mmol) of methyl
p-[2-(5-cyano-6-methoxy-3,4-dihydro-2-pyridon-3-yl)ethyl]-
benzoate (12c). Reflux time was 38 h. The yield was 1.22 g
(3.6 mmol, 97%) of 13c as a colorless solid: mp 320 °C dec; IR
(KBr) 3500, 3380, 3330, 3200, 3160 (N-H), 1700 (COOMe),

3544 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 18
Notes
1680 (CONH), 1630, 1570 (CdC, CdN) cm-1; MS FAB(+) m/z
364 [M + Na]+, 342 [M + H]+, 341 [M+]. Anal. (C17H19N5O3)
C, H, N.
resulting solution was carefully acidified (pH ) 6-7) with 25%
aqueous acetic acid and stirred in the cold for 2 h. The
resulting solid was filtered (or centrifugated), washed with
water, and dried over P2O5 to give 0.420 g (0.9 mmol, 89%) of
16a as a colorless solid: mp 230 °C; IR (KBr) 3500-2500
(COO-H), 3420, 3360, 3210 (N-H), 1640 (CdO), 1610, 1560,
1500 (CdC, CdN), 765 cm-1; 1H NMR (TFA-d), δ 2.34 (br, 1H,
C3-H), 2.54 (br, 1H, C3-H), 2.68-2.86 (m, 3H, C4-H, C5′′-
H), 3.05-3.08 (m, 1H, C5′′-H, C6′′-H), 3.50 (s, 3H, N-CH3),
3.98-4.08 (m, 1H, C6′-H), 4.18-4.21 (m, 1H, C6′-H), 5.02 (br,
Gen er a l Meth od for th e Hyd r olysis of th e Ester
Gr ou p
p-[N-(2,4-Dia m in o-7-oxo-5,6,7,8-tetr a h yd r op yr id o[2,3-d ]-
p yr im id in -6-ylm eth yl)-N-m eth yla m in o]ben zoic Acid
p r esen t
in
P yr id o[2,3-d ]p yr im id in es 13.
(14a ). A suspension of 500 mg (1.4 mmol) of methyl
p-[N-(2,4-dia m in o-7-oxo-5,6,7,8-t et r a h ydr opyr ido[2,3-d ]-
pyrimidin-6-ylmethyl)-N-methylamino]benzoate (13a ) in
a
3
1H, C2-H), 7.77 (AA′BB′, J HH ) 8 Hz, 2H, C3′-H), 8.06
0.5 N aqueous solution of NaOH was heated at reflux until
dissolution of the solid and then was stirred at room
temperature for 12 h. The resulting solution was filtered
3
(AA′BB′, J HH ) 8 Hz, 2H, C2′-H); 13C NMR (TFA-d), δ 21.4
(C5′′), 27.8 (C3), 31.7 (C4), 36.1 (C6′′), 49.0 (N-CH3), 55.0 (C2),
62.1 (C6′), 82.3 (C4′′a), 124.0 (C3′), 132.6 (C2′), 137.9 (C1′),
144.0 (C4′), 155.0 (C8′a), 156.2 (C4′, C2′), 171.1 (C1′-CONH),
176.0 (C7′′), 178.4 (C5), 182.0 (C1); HRMS FAB(+) calcd for
C21H26N7O6 [M + H], 472.1945; found, 472.1939. Anal.
(C21H25N7O6‚2.5H2O) C, H, N.
through
a Lida filter (47-mm filter membrane, 0.45 µm
nylon, art. NY504700, Lida Manufacturing Corp., 9115 26th
Avenue, Kenosha, WI), and the filtrate was acidified with
concentrated acetic acid. The resulting precipitate was
filtered (sometimes a centrifugation was required), washed
with water, and dried over P2O5 to give 532 mg (1.35 mmol,
96%) of 14a ‚3H2O as a colorless solid: mp 202-209 °C
dec; IR (KBr) 3500-2500 (COO-H and N-H), 1660 (CdO),
N-{p-[N-(2,4-Dia m in o-7-oxo-5,6,7,8-tetr a h yd r op yr id o-
[2,3-d]pyr im idin -6-ylm eth yl)am in o]ben zoyl}glu tam ic Acid
(16b). The procedure was the same as that stated above for
16a but using 0.468 g (1.4 mmol) of p-[N-(2,4-diamino-7-oxo-
5,6,7,8-tetrahydropyrido[2,3-d]pyrimidin-6-ylmethyl)amino]-
benzoic acid (14b) in 20 mL of anhydrous DMF, 0.345 g (3.4
mmol) of Et3N, 0.558 g (3.4 mmol) of diethyl cyanophospho-
nate, 0.345 g (3.4 mmol) of Et3N, and 0.723 g (3.4 mmol) of
L-glutamic acid dimethyl ester hydrochloride to afford 0.583 g
(1.2 mmol, 84%) of dimethyl N-{p-[N-(2,4-diamino-7-oxo-5,6,7,8-
tetrahydropyrido[2,3-d]pyrimidin-6-ylmethyl)amino]benzoyl}-
glutamate (15b) as a colorless solid: mp 172-174 °C; IR (KBr)
3330, 3200 (N-H), 1730 (COOMe), 1675, 1635 (CONH), 1600,
1560, 1500 (CdC, CdN), 770 cm-1; MS m/z 191 (26) [C8H9N5O+],
120 (100). Then, using 0.492 (1.0 mmol) of 15b in 8.5 mL of
1 N aqueous NaOH gave 0.380 g (0.8 mmol, 83%) of 16b as a
colorless solid: mp >200 °C dec; IR (KBr) 3500-2500 (COOH),
3350, 3210 (N-H), 1650 (CdO), 1610, 1560, 1510 (CdC, Cd
1600, 1560 (CdC, CdN), 775 cm-1
; MS m/z 191 (35)
[C8H9N5O+], 151 (100), 134 (53). Anal. (C16H18N6O3‚3H2O)
C, H, N.
p-[N-(2,4-Dia m in o-7-oxo-5,6,7,8-tetr a h yd r op yr id o[2,3-
d ]p yr im id in -6-ylm eth yl)a m in o]ben zoic Acid (14b). The
procedure was the same as that stated above for 14a but using
1.000 g (3 mmol) of methyl p-[N-(2,4-diamino-7-oxo-5,6,7,8-
tetrahydropyrido[2,3-d]pyrimidin-6-ylmethyl)amino]ben-
zoate (13b) in 15 mL of a 1 N aqueous solution of NaOH. Yield
was 1.030 g (3 mmol, 99%) of 14b‚1.5H2O as a colorless solid:
mp 285-287 °C; IR (KBr) 3500-2500 (COO-H and N-H),
1700 (CdO), 1650, 1600 (CdC, CdN), 780 cm-1; MS m/z 191
(100) [C8H9N5O+], 137 (31), 120 (49). Anal. (C15H16N6O3‚
1.5H2O) C, H, N.
p -[2-(2,4-Dia m in o-7-oxo-5,6,7,8-t et r a h yd r op yr id o[2,3-
d ]p yr im id in -6-yl)eth yl]ben zoic Acid (14c). The procedure
was the same as that stated above for 14a but using 1.70 g (5
mmol) of methyl p-[2-(2,4-diamino-7-oxo-5,6,7,8-tetrahydro-
pyrido[2,3-d]pyrimidin-6-yl)ethyl]benzoate (13c) in 100 mL of
a 1 N aqueous solution of NaOH. A digestion in acetic acid of
the crude material obtained gave 1.79 g (4.6 mmol, 92%) of
14c‚CH3CO2H as a colorless solid: mp >275 °C; IR (KBr)
3500-2500 (COO-H and N-H), 1710 (CdO), 1680-1620 (Cd
O,CdC,CdN),1560(CdC,CdN),770cm-1. Anal. (C16H17N6O3‚CH3-
CO2H) C, H, N.
1
N), 770 cm-1; H NMR (TFA-d), δ 2.31-2.38 (m, 1H, C3-H),
2.55-2.77 (m, 4H, C3-H, C4-H, C5′′-H), 3.17-3.14 (m, 1H,
C5′′-H), 3.58 (br, 1H, C6′′-H), 3.86-3.90 (m, 1H, C6′-H), 4.00-
3
3
4.07 (m, 1H, C6′-H), 4.95 (dd, J HH ) 5 Hz, J HH ) 8 Hz, 1H,
3
C2-H), 7.77 (AA′BB′, J HH ) 8 Hz, 2H, C3′-H), 8.09 (AA′BB′,
3J HH ) 8 Hz, 2H, C2′-H); 13C NMR (TFA-d), δ 21.5 (C5′′), 27.6
(C3), 31.5 (C4), 36.8 (C6′′), 54.8 (C2), 55.0 (C6′), 86.6 (C4′′a),
125.1 (C3′), 132.1 (C2′), 137.0 (C1′), 139.1 (C4′), 154.6 (C8′a),
155.6 (C4′), 157.0 (C2′), 171.4 (C1′-CONH), 176.3 (C7′′), 178.5
(C5), 181.9 (C1); HRMS FAB(+) calcd for C20H24N7O6 [M +
H], 458.1788; found, 458.1781. Anal. (C20H23N7O6‚0.5CH3-
CO2H‚1.5H2O) C, H, N.
Gen er a l Meth od for th e Syn th eses of 16a -c. N-{p-[N-
(2,4-Dia m in o-7-oxo-5,6,7,8-tetr a h yd r op yr id o[2,3-d ]p yr i-
m idin -6-ylm eth yl)-N-m eth ylam in o]ben zoyl}glu tam ic Acid
(16a ). To a solution of 1.00 g (2.9 mmol) of p-[N-(2,4-diamino-
7-oxo-5,6,7,8-tetrahydropyrido[2,3-d]pyrimidin-6-ylmethyl)-N-
methylamino]benzoic acid (14a ) in 50 mL of anhydrous DMF
in an inert atmosphere was added 0.74 g (7.3 mmol) of Et3N.
The resulting mixture was stirred at room temperature for
10 min. Then 1.19 g (7.3 mmol) of diethyl cyanophosphonate
was added, and the resulting mixture was stirred for 4 h. Next,
0.74 g (7.3 mmol) of Et3N and 1.54 g (7.3 mmol) of L-glutamic
acid dimethyl ester hydrochloride were added. The mixture
was stirred for 24 h at room temperature in an inert atmo-
sphere. The solution was concentrated in vacuo, and the
resulting solid was suspended in water, basified with an
aqueous solution of NaHCO3, sonicated, filtered (or centrifu-
gated), washed with water and with MeOH, and dried over
P2O5 to give 1.02 g (2.0 mmol, 70%) of dimethyl N-{p-[N-(2,4-
diamino-7-oxo-5,6,7,8-tetrahydropyrido[2,3-d]pyrimidin-6-yl-
methyl)-N-methylamino]benzoyl}glutamate (15a ) which was
used without further purification: mp 172-175 °C; IR (KBr)
3450, 3330, 3205 (N-H), 1740 (COOMe), 1685, 1635 (CONH),
1605, 1570, 1510 (CdC, CdN), 775 cm-1; HRMS FAB(+) calcd
N-{p -[2-(2,4-Dia m in o-7-oxo-5,6,7,8-t et r a h yd r op yr id o-
[2,3-d ]p yr im id in -6-yl)eth yl]ben zoyl}glu ta m ic Acid (16c).
The procedure was the same as that stated above for 16a but
using 0.458 g (1.4 mmol) of p-[2-(2,4-diamino-7-oxo-5,6,7,8-
tetrahydropyrido[2,3-d]pyrimidin-6-yl)ethyl]benzoic acid (14c)
in 20 mL of anhydrous DMF, 0.345 g (3.4 mmol) of Et3N, 0.558
g (3.4 mmol) of diethyl cyanophosphonate, 0.345 g (3.4 mmol)
of Et3N, and 0.723 g (3.4 mmol) of L-glutamic acid dimethyl
ester hydrochloride to afford 0.549 g (1.1 mmol, 81%) of
dimethyl N-{p-[2-(2,4-diamino-7-oxo-5,6,7,8-tetrahydropyrido-
[2,3-d]pyrimidin-6-yl)ethyl]benzoyl}glutamate (15c) as a color-
less solid: mp >300 °C; IR (KBr) 3320, 3210 (N-H), 1740
(COOMe), 1650 (CONH), 1570, 1500 (CdC, CdN), 790 cm-1
.
Then, using 1.000 g (2.1 mmol) of 15c in 16 mL of 1 N aqueous
NaOH afforded 1.008 g (2.0 mmol, 94%) of 16c‚3.5H2O as a
colorless solid: mp 246-247 °C; IR (KBr) 3600-2500 (COO-
H), 3330, 3200 (N-H), 1630-1670 (CdO), 1540, 1490 (CdC,
1
CdN), 760 cm-1; H NMR (TFA-d), δ 2.12-2.20 (m, 2H, C6′-
H), 2.29-2.42 (m, 1H, C3-H), 2.53-2.62 (m, 1H, C3-H),
2.66-2.97 (m, 7H, C5′′-H, C6′′-H, C5′-H, C4-H), 5.03 (dd, 3J HH
3
3
) 5 Hz, J HH ) 9 Hz, 1H, C2-H), 7.34 (AA′BB′, J HH ) 8 Hz,
2H, C3′-H), 7.75 (AA′BB′, J HH ) 8 Hz, 2H, C2′-H); 13C NMR
3
for
C
23H30N7O6 [M + H], 500.2258; found, 500.2248.
A
suspension of 0.500 g (10 mmol) of 15a in 8 mL of a 1 N
aqueous solution of NaOH was stirred at room temperature
for 24 h. The solution obtained was filtered through a Lida
filter (47 mm, 0.45 µm nylon) and cooled in an ice bath. The
(TFA-d), δ 26.2 (C5′′), 27.8 (C3), 31.6 (C4), 34.5 (C6′), 35.3 (C5′),
44.5 (C6′′), 55.0 (C2), 84.2 (C4′′a), 129.6 (C3′), 131.0 (C2′), 131.1
(C1′), 149.0 (C4′), 151.4 (C8′a), 155.8 (C4′, C2′), 174.5 (C1′-
CONH), 178.6 (C7′′), 182.2 (C5), 183.3 (C1); HRMS FAB(+)

Notes
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 18 3545
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calcd for C21H25N6O6 [M + H], 457.1836; found, 457.1826.
Anal. (C21H24N6O6‚3.5H2O) C, H, N.
In Vitr o Cell Cu ltu r e Stu d ies. Dose response curves were
generated to determine the concentration required for 50%
inhibition of growth (IC50) of CCRF-CEM human leukemia
cells.27 Test antifolate compounds were dissolved initially in
pure DMSO at a concentration of 4 mg/mL and further diluted
with cell culture medium (Roswell Park Memorial Institute,
RPMI-1640 media) to the desired concentration. CCRF-CEM
leukemia cells in complete medium were added to 24-well
cluster plates at a final concentration of 4.8 × 104 cells/well
in a total volume of 2.0 mL. Test compounds at various
concentrations were added to duplicate wells so that the final
volume of DMSO was 0.5%. The plates were incubated for 72
h at 37 °C in a 5% CO2-in-air atmosphere. At the end of the
incubation, cell numbers were determined on a ZBI Coulter
counter. Control wells usually contained (4-6) × 105 cells at
the end of the incubation.
Ack n ow led gm en t. The authors warmly thank Dr.
Chuan Shih (Lilly Research Laboratories, Indianapolis,
IN) for his very useful comments throughout this work.
We also thank Lilly Research Laboratories for the in
vitro cell culture studies. Support of this work by a grant
from the Comisio´n Interdepartamental de Ciencia y
Tecnolog´ıa and the Comissio´ Interdepartamental de
Recerca i Innovacio´ Tecnolo´gica within the Programa
de Qu´ımica Fina (QFN93-4420) is gratefully acknowl-
edged. B.M.-T. thanks Fundacio´n J uan Salan˜er for a
grant.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR and 13C
NMR spectral data for compounds 11a -c, 12a -c, 13a -c,
14a -c, and 15a -c (4 pages). Ordering information is given
on any current masthead page.
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