Synthesis of agonists and antagonists for central glutamate receptors by a novel 'ring switching' strategy

Article abstract of DOI:10.1039/a608067g

A novel and versatile ring switching strategy has been developed for the synthesis of compounds with structural features consistent with activity at glutamate receptors. A variety of homochiral L-alanine derivatives substituted at the β-carbon atom with planar five and six-membered heteroaromatic rings have been prepared in a one- or two-pot reaction using this strategy and some of the products have been shown to have biological activity at central glutamate receptors.

Full text of DOI:10.1039/a608067g

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Synthesis of agonists and antagonists for central glutamate
receptors by a novel ‘ring switching’ strategy1
Andrew N. Bowler, Andrew Dinsmore, Paul M. Doyle and Douglas W. Young*
School of Chemistry and Molecular Sciences, University of Sussex, Falmer, Brighton,
UK BN1 9QJ
A novel and versatile ring switching strategy has been developed for the synthesis of compounds with
structural features consistent with activity at glutamate receptors. A variety of homochiral L-alanine
derivatives substituted at the â-carbon atom with planar five and six-membered heteroaromatic rings have
been prepared in a one- or two-pot reaction using this strategy and some of the products have been shown
to have biological activity at central glutamate receptors.
Since the excitatory action of -glutamic acid 1 on single neu-
rones in the central nervous system was first demonstrated by
N(CH3)2
6
H
H
OHC
O
Curtis et al. in 1959,2 a number of structurally related amino
acids have been tested as agonists and antagonists. This led
to the realisation that there are several different sub-types of
glutamate receptors. The implication of these receptors in
memory processes and Alzheimer’s disease3 and the potential
of excitatory amino acid antagonists in anti-epileptic therapy4
and in limiting the damage caused following a stroke5 has
initiated great interest in the field.
The discovery that ibotenic acid 2, the active component of
the psychotropic fly agaric mushroom Amanita muscaria Fr.,
had potent neuroexcitatory properties led to the synthesis of a
number of heterocyclic analogues of glutamic acid 6–12 and the
compound (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)-
propanoic acid (AMPA, 3) was prepared.6 The 3-hydroxy-
isoxazole moiety in these compounds acts as a bioisostere of
the γ-carboxy group of (S)-glutamic acid 1 and, whereas ibo-
tenic acid 2 seems to activate the NMDA sub-type of glutamate
receptor, AMPA 3 is a potent agonist at a different sub-type of
glutamate receptor. The syntheses of the heterocyclic analogues
were lengthy and non-versatile and led to racemic products.
When the enantiomers were separated, it was found that there
was pronounced receptor stereoselectivity, with compounds of
the -configuration often being the more active.13–15 Synthesis
of conformationally restricted analogues has led to some
understanding of the spatial requirements of the receptors.16
4
H
H
H
O
O
N
N
N
CO2Bn
CO2Bn
CO2Bn
CO2Bn
CO2Bn
CO2Bn
4
5
6
H
H
H
N
N
N
H
H
HX
X
O
NH CO2Bn
CO2Bn
CO2Bn
OH
CO2Bn
8
7
Scheme 1
antagonist. We have termed this reaction, where a heterocyclic
ring is generated at the expense of the pyroglutamate ring, a
‘ring switching’ process.1
The enaminone 5 was, therefore, hydrolysed to the aldehyde 6
in methanol and then treated in situ either directly at pH 1 or
buffered at pH 5 with an appropriate nucleophile. When the
reaction was carried out at pH 5 and room temperature using
methylhydrazine, TLC initially showed the presence of two new
compounds but one was converted into the other within 15 h.
The final product was purified by chromatography to give a
gum, C22H23N3O5, λmax 254 nm, which showed loss of the
characteristic imide absorption at 1760 cmϪ1 present in the IR
spectrum of the starting material. This and the 1H NMR spec-
trum in [2H6]-DMSO which showed an additional aromatic
singlet at δ 7.07 and a clear ᎐NHCHCH2᎐ system at 7.90 (NH,
exchangeable), 4.18 (α-CH, q) and 2.74 and 2.58 (β-CH2) sug-
gested the structure 9b and the other data were in accord with
this assignment. Acetylation of the product using acetic
anhydride and DMAP in acetonitrile at room temperature gave
the acetate, C24H25N3O6 in 50% yield. This showed a consider-
able shift in the UV spectrum to higher wavelength (λmax 332
nm) and a 13% NOE for the aromatic singlet at δ 8.17 in the 1H
NMR spectrum when the acetyl methyl singlet at δ 2.31 was
irradiated. This indicated that acetylation had occurred at
nitrogen in the pyrazolone tautomer to yield the fully conju-
gated compound 10b.
OH
OH
HO
N
O
H
CO2H
NH2
O
H
N
H
O
CO2H
H2N
CO2H
H3C
H2N
1
2
3
Because of the lack of versatility and the large number of
steps in the existing syntheses of AMPA agonists and antagon-
ists and the fact that these syntheses led to racemates, we have
now devised a more versatile synthesis leading to homochiral
protected AMPA analogues in a one- or two-pot process. In this
synthesis we have converted benzyl N-benzyloxycarbonyl-
(2S)-pyroglutamate 417 into the enaminone 5 using tert-
butoxybis(dimethylamino)methane following the method of
Danishefsky et al.18 We have shown that this and related com-
pounds can be hydrolysed to the aldehyde 6 under carefully
controlled conditions19,20 and we reasoned that, if this were
allowed to react in situ with a suitable α-nucleophile, then the
resultant intermediate 7 might undergo intramolecular nucleo-
philic attack at the ring carbonyl group as in Scheme 1 to yield
a homochiral compound 8 with a heterocyclic moiety at the β-
carbon atom of an alanine moiety. Such a compound would
have the structural features required of a glutamate agonist or
When the aldehyde 6 was prepared in situ and allowed to
react with hydrazine hydrate at pH 5, the reaction took a similar
course to that above. An intermediate compound was seen on
TLC and a final product, C21H21N3O5, was obtained with simi-
lar UV characteristics to those of compound 9b. The chemical
shift for the new one-proton aromatic singlet at δ 7.17 in [2H6]-
DMSO was also similar to that in the former compound and so,
although the scope for tautomerism is greater in this com-
J. Chem. Soc., Perkin Trans. 1, 1997
1297

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H
H
pound, we prefer the structure 9a rather than the alternative
structure 11. When this compound was acetylated, however, the
monoacetate had a significantly different UV spectrum (λmax
290 nm) to that of the acetate 10b which suggested structure 12.
This was supported by the fact that no NOE was observed
between the acetyl methyl group and the aromatic proton.
Reaction of the aldehyde 6 with phenylhydrazine at pH 5 gave
the expected product 9c but when p-nitrophenylhydrazine was
used, the reaction was pH dependent, giving the expected pyra-
zole 9d at pH 5 but yielding the p-nitrophenylhydrazone 13d
as a mixture of stereoisomers when the reaction was conducted
at pH 1. Acetylation of the pyrazole 9c gave two unstable prod-
ucts which could not fully be characterised. When the corre-
sponding p-nitrophenyl derivative 9d was acetylated, however,
then the two products, although unstable, were obtained in a
sufficiently pure state for the spectra to suggest that the major
isomer was the pyrazolone 10d and the minor isomer was the
enol acetate 14.
Me
3′
3′
3
3
N
H
O
N
H
2
2
N
N
NH CO2Bn
CO2Bn
NH CO2Bn
CO2Bn
R
OH
R
O
a R = H
b R = Me
c R = Ph
a R = H
10
b R = Me
d R = p-NO2C6H4
9
d R = p-NO2C6H4
H
H
3′
3
3
HN
H
HN
H
N
N
NH CO2Bn
CO2Bn
NH CO2Bn
CO2Bn
1′
O
O
OH
CH3
11
12
H
H
H
3′
RHN
3
Reaction of the aldehyde with 2,4-dinitrophenylhydrazine
gave only a diastereoisomeric mixture of 2,4-dinitrophenyl-
hydrazones 13e and it was not possible to obtain a ring-
switched product when this hydrazine was used.
6
N
N
H
4
H
2
N
O
NH CO2Bn
N
CO2Bn
p-NO2C6H4
OAc
CO2Bn
CO2Bn
14
These results indicated that the reactions had proceeded via
the hydrazones 7 (X = NR) which could then undergo a ‘ring
switching’ reaction to the pyrazolones 9 if the second nitrogen
atom was sufficiently nucleophilic. Although all of the prod-
ucts had optical rotations, we were able to check that the chiral
centre at C-2 of the protected glutamate derivative 8 remained
intact by repeating the reaction with hydrazine hydrate using
2HCl and MeO2H. Although the major product in this case
was the acetal 15 which had evidently incorporated deuterium
at C-4, the pyrazolone 9a obtained contained no non-
exchangeable deuterium as evidenced by mass spectrometry
13
d R = p-NO2C6H4
e R = 2,4-(NO2)2C6H3
H
H
2 H
6
3′
MeO
MeO
3
2
N
O
H
4
H
O
NH CO2Bn
CO2Bn
N
OH
16
CO2Bn
CO2Bn
15
H
H
6
H
3′
PhCH2O
3
N
1
2
N
O
H
4
and H and H NMR spectroscopy.
H
2
O
When the aldehyde 6 was prepared and allowed to react in
situ with hydroxylamine at pH 5, an unstable product was
obtained which had spectra consistent with the isoxazole struc-
ture 16. Although there was no sign of an intermediate oxime
in this case, reaction with O-benzylhydroxylamine gave the
O-benzyl derivative 17 as a mixture of 4R, 4S and syn and anti
isomers. Acetylation of the isoxazole 16 led to a stable acetate
which appeared to be the enol acetate 18, with νmax 1771 cmϪ1
and no amide absorption in the IR spectrum.
NH CO2Bn
N
CO2Bn
OAc
CO2Bn
CO2Bn
17
18
H
H
3′
3′
3
3
N
O
H
N
N
H
2
2
H2N
CO2H
H2N
CO2H
OH
R
OH
a R = H
b R = Me
20
19
Subsequent to our synthesis of these compounds, the anti-
fungal antibiotic TAN-950 was isolated from culture filtrates
of Streptomyces platensis A-136.21 This was shown to be the
isoxazole 19 and was present in equilibrium with the stereo-
isomeric pyroglutamic acid 4-oximes. It exhibited affinity for
excitatory amino acid receptors in the rat brain.21
alternative approach was sought. Using the tert-butyl ester of
the tert-butoxycarbonyl enaminone 23,25 careful acid hydrolysis
gave the aldehyde 24 which, on treatment with diazomethane,
yielded the enol ether 25 in 74% overall yield. Attempts to form
useful ‘ring-switched’ products by allowing this to react with
urea, thiourea or guanidine failed but, when heated with aceta-
midine hydrochloride and K2CO3 in ethanol at reflux, it gave the
2-methylpyrimidin-4-one 26b in 87% yield. The 1H NMR spec-
trum showed the expected exchangeable NH absorption coup-
led to the α-amino acid proton, a feature which was not present
in the spectrum of the starting material, and the absence of an
imide absorption at 1759 cmϪ1 in the IR spectrum which was
present in the starting material. The UV spectrum was consist-
ent with the behaviour expected of a 2,5-dialkylpyrimidin-4-
one,26 exhibiting λmax 276 nm, reversibly shifting to λmax 263 nm
Having developed a versatile route to potential glutamate
agonists and antagonists, we now investigated deprotection of
the compounds 9a and 9b by hydrogenolysis. Initial attempts
to hydrogenolyse 9a using 10% palladium-on-charcoal in
methanol gave a mixture of the expected product 20a and the
partially deprotected acid 21 and so we conducted the sub-
sequent reactions in glacial acetic acid using Adam’s catalyst.
The resultant amino acids 20a and 20b both demonstrated an
inhibitory effect on ibotenate stimulated phosphoinositide
response, although they were two-fold less potent than the
selective inhibitor L-AP3.22 The amino acid 20a [IC50
300 ± 30 µm (n = 3)] was slightly more potent than 20b [IC50
=
=
1
on addition of acid. The H NMR spectrum also appeared to
380 ± 86 µm (n = 3)]. The inhibitory effects were not reversed by
higher agonist concentration.
show the presence of a second compound (ca. 2:8 by integra-
tion) in spite of its sharp melting point, analytical purity and
apparent chromatographic homogeneity. The spectrum associ-
ated with the minor component at room temperature in [2H6]-
DMSO coalesced with that of the major component at 80 ЊC in
this solvent, suggesting the presence of two conformational
isomers. When either the aldehyde 24 or the enaminone 23 was
used in this synthesis, the pyrimidinone 26b was obtained but in
lesser yield than in the reaction with the enol ether 25.
The reported activity of willardiine 22 at glutamate recep-
tors23,24 suggested that extension of our synthesis to include
-alanine derivatives substituted in the β-position by six-mem-
bered ring heteroaromatic compounds might yield biologically
interesting compounds. We therefore treated the poorer nucleo-
philes urea, thiourea and guanidine directly with the aldehyde
6, prepared in situ. This method proved ineffective and so an
1298
J. Chem. Soc., Perkin Trans. 1, 1997

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H
O
3′
H
4′
4′
3
N
N
N
2′
N
H
O
N
O
H
R
2′
3
H2N
H
H
N
N
2
N
2
HN
CO2H
H2N
22
CO2H
H
H
OH
H
HN
CO2But
H2N
CO2H
H
CO2CH2Ph
O
CO2But
21
27 a R = H
b R = Me
c R = Ph
28
N(CH3)2
6
H
H
OHC
O
4
H
H
4′
4′
N
H
H
2′
N
H2N
2
2′
3
O
MeO
H
H
CO2But
CO2But
CO2But
N
N
N
2
N
CO2But
H
HN
CO2But
H2N
CO2H
H
O
O
N
CO2But
23
24
29
30
H
2′
OMe
6
N
H
O
6
H
2′
N
4
H
CO2But
NHBoc
4′
H
N
3
2′
H
4
N
3
R
H
H
2
2
3
O
N
CO2But
O
N
2
CO2But
N
O
HN
CO2But
H
CO2But
CO2But
CO2But
31
32
25
26 a R = H
b R = Me
c R = Ph
H
H
N
N
N
2′
N
O
N
Scheme 2
2M′ e
CO2H
NH2
6
N
H
N
2
4
H
3
Reaction of the enol ether 25 with benzamidine hydro-
chloride and with formamidine acetate, under the conditions
used in the reaction of the enol ether with acetamidine hydro-
chloride above, gave the pyrimidinones 26c (55%) and 26a
(76%). Both compounds had spectra in keeping with those of
the methyl analogue 26b, including the variable-temperature 1H
NMR spectral effect ascribed to conformational isomerism. All
three pyrimidinones were cleanly deprotected by treatment with
concentrated hydrochloric acid at room temperature, giving the
hygroscopic amino acid hydrochlorides 27b, 27c and 27a.
Compound 27a was tested for activity and found to be a
glutamate agonist.27,28
The enol ether 25 did not react with guanidine hydrochloride
and potassium carbonate in ethanol at reflux but, when heated
with guanidine carbonate in ethanol at reflux, it gave a mixture
of two compounds. One of these proved to be the desired
2-aminopyrimidinone 28 (39%). This showed the variable-
temperature 1H NMR spectral effects exhibited by related
compounds in the series and was deprotected using concen-
trated hydrochloric acid at room temperature to yield the amino
acid hydrochloride 29, which was a weak antagonist to ACPD
at the metabotropic receptor.27,28 Attempts to prepare the
2-methoxypyrimidinone 30 by treating the enol ether 25 with
O
CO2But
N
CO2But
33
34
N
O
N
H
CO2But
NHBoc
N
N
N
H
35
heated the 4-formylpyroglutamate 24 with aminotetrazole in
dioxane at reflux and obtained the enaminone 34 [mp 183 ЊC
(decomp.); λmax 297 nm] in 70% yield. A number of attempts
were made to convert this compound into the pyridotetrazole
35 by the ring-switching reaction but none were successful.
Experimental
Melting points were determined on a Kofler hot-stage appa-
ratus and are uncorrected. IR Spectra were recorded on a
Perkin-Elmer 1720 Fourier transform instrument and UV
spectra in methanol on Philips PU8720 and PU800 spectro-
photometers or on a Perkin-Elmer PE 330 instrument. 1H
NMR Spectra were recorded on Bruker WM360 (360 MHz),
AMX 500 (500 MHz) or AC-200 (200 MHz) Fourier transform
instruments. J Values are given in Hz. 13C NMR Spectra were
recorded on Bruker AMX 500 (125.76 MHz), WM360 (90.6
MHz), AC-200 (50.3 MHz) or Bruker 250 (62.9 MHz) spectro-
meters. INEPT Experiments were used to help assign 13C reson-
ances where necessary. The residual solvent peak was used as
reference for all NMR spectra. Low resolution mass spectra
were recorded on Kratos MS80, MS25 or MS50 instruments.
Accurate mass measurements were recorded on a VG7070
instrument by Dr S. Chotai (Wellcome Research Laboratories)
and microanalyses were performed by Mrs K. Plowman and
Miss M. Patel at the University of Sussex and by Mrs P.
Firmin at Wellcome Research Laboratories. Optical rotations
were measured on a Perkin-Elmer PE241 polarimeter using a
1 dm path length micro cell; they are recorded as 10Ϫ1 deg
1
O-methylisourea seemed to be partly successful from the H
NMR spectrum of the crude product but we were unable to
purify the product fully.
In an attempt to extend the synthesis to polycyclic aromatic
analogues of glutamate agonists and antagonists, the enol ether
25 was heated with 2-aminopyridine in ethanol at reflux but
no reaction was observed. When the aldehyde 24, prepared
independently by treating tert-butyl 1-tert-butoxycarbonylpyro-
glutamate with lithium hexamethyldisilazide in THF followed
by addition of methyl formate, was allowed to react with
2-aminopyridine in dioxane at reflux, a product was obtained
in 68% yield. This still retained the imide absorption due to the
N-tert-butoxycarbonylpyroglutamate system in the IR spec-
trum and microanalytical and spectral data indicated that it was
the enaminone 31 (λmax 287 and 335 nm). This compound was
heated with potassium carbonate in ethanol at reflux to yield
the desired pyrido[1,2-a]pyrimidine 32 (λmax 242 and 339 nm) in
55% yield. Deprotection with concentrated hydrochloric acid at
room temperature gave the hydrochloride of the amino acid 33,
in quantitative yield.
cm2
g
Ϫ1. Thin layer chromatography was carried out using
Merck Kieselgel 60 F254 pre-coated silica gel plates of thickness
0.2 mm (ART 5554 and ART 5714) and column chrom-
atography was performed using Merck Kieselgel 60 (230–400
mesh, ART 9385) unless otherwise stated.
In an attempt to obtain the fused ring system 35, we first
J. Chem. Soc., Perkin Trans. 1, 1997
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Benzyl (2S)-1-benzyloxycarbonyl-4-dimethylaminomethylene-
pyroglutamate 5
(urethane and ester) and 1657 (amide and pyrazolone);
λmax(MeOH, pH 7)/nm 281 and 332 (ε 9130 and 1280); λmax
(MeOH, pH 12)/nm 243 and 330 (ε 5050 and 1330); λmax
-
-
This compound was prepared by the following adaptation of
the method of Danishefsky et al.18 Benzyl (2S)-1-benzyloxy-
carbonylpyroglutamate 417 (40.0 g, 0.113 mol) was dissolved
in dimethoxyethane (350 ml) and tert-butoxybis(dimethyl-
amino)methane (Bredereck’s reagent) (29.6 g, 0.170 mol) was
added to the solution. The reaction mixture was heated at a
constant temperature of 75 ЊC for 14 h after which the solvent
was removed in vacuo to afford a brown oil which was crystal-
lised from toluene–light petroleum (bp 60–80 ЊC) as a light
yellow solid (41.1 g, 89%); mp 92–94 ЊC (lit.,18 92–93 ЊC); [α]D26
Ϫ29.9 (c 0.81, CHCl3) [lit.,18 [α]D Ϫ32.8 (c 1.4, CHCl3)] (Found:
C, 67.2; H, 6.0; N, 6.8. C23H24N2O5 requires C, 67.6; H, 5.9; N,
6.9%); m/z [ϩve FAB (NBA)] 409 ([M ϩ H]ϩ); νmax(KBr)/cmϪ1
1760 (imide); λmax(MeOH)/nm 313 (ε 29 200); δH (360 MHz,
C2HCl3) 7.33 (10 H, m, ArH), 7.17 (1 H, t, J6,3A-6,3B 1.6,
CHNMe2), 5.21 (2 H, AB, JAB 12.5, PhCH2O), 5.11 (2 H, AB,
JAB 12.1, PhCH2O), 4.66 (1 H, d × d, J2,3S 10.6, J2,3R 3.6, H-2),
3.26 (1 H, m, J3S,2 10.6, J3S,3R 14.6, H-3S), 3.01 [6 H, s, N(CH3)2]
and 2.90 (1 H, m, J3R,2 3.6, J3R,3S 14.6, H-3R).
(MeOH, pH 2)/nm 281 and 332 (ε 12 400 and 1630); δH (200
MHz, [2H6]-DMSO) 8.17 (1 H, s, H-3Ј), 7.84 (1 H, br d, JN H ,2
7.7, NH), 7.33 (10 H, s, ArH), 5.10 and 5.03 (4 H, 2 × s,
2 × PhCH2), 4.41 (1 H, q, J2,3B = J2,3A = J2,N H = 7, H-2), 3.40
(3 H, s, N–CH3), 2.68 (2 H, m, overlapping, J3B,3A 14.1,
J3B,2 = J3A,2 = 7, 3-CH2) and 2.31 (3 H, s, CH3CO). Irradiation
of CH3CO (δ 2.31) produced a 13% enhancement in H-3Ј
(δ 8.17). Irradiation of H-3Ј gave an enhancement of 4% in
CH3CO; δC(50.3 MHz, [2H6]-DMSO) 171.85 (ester), 167.20
(C-5Ј), 164.86 (amide), 156.50 (urethane), 137.04 and 136.01
(2 × ipso C), 136.76 (C-3Ј), 128.94–128.07 (aromatic), 110.35
(C-4Ј), 66.83 and 66.24 (2 × PhCH2), 53.19 (C-2), 34.00
(N–CH3), 25.17 (C-3) and 21.84 (N–COCH3).
Benzyl (2S)-2-benzyloxycarbonylamino-3-(5-hydroxypyrazol-
4-yl)propionate 9a
Compound 5 (250 mg, 0.61 mmol) was dissolved in methanol
(10 ml) and 1  aqueous hydrochloric acid was added dropwise
to the solution until its UV spectrum showed reaction to be
complete (ca. 1.5 equiv. was required). Hydrazine hydrate (30 µl,
0.62 mmol; 98%) was then added to the mixture at room tem-
perature, giving a deep yellow colouration. After being stirred
at room temperature for 18 h, the solvent was removed in vacuo
and the residue was partitioned between ethyl acetate and
water. The organic phase was washed consecutively with satur-
ated aqueous sodium hydrogen carbonate, water and brine and
then dried (Na2SO4). The solvent was removed in vacuo to
afford a yellow foam (80% yield). This was chromatographed
on silica gel using gradient elution from light petroleum (bp 60–
80 ЊC)–ethyl acetate (1:9) to pure ethyl acetate. The title com-
pound 9a was obtained as a colourless gum which could not be
crystallised (71 mg, 30%); [α]2D8 Ϫ11.0 (c 0.39, CHCl3) (Found:
C, 62.1; H, 5.2; N, 10.2. C21H21N3O5ؒ0.5H2O requires C, 62.4;
H, 5.45; N, 10.4%) [Found: m/z (EI) 395.1479 ([M]ϩ).
C21H21N3O5 requires 395.1476]; νmax(CHCl3)/cmϪ1 3324 (NH,
Benzyl (2S)-2-benzyloxycarbonylamino-3-(1-methyl-5-hydroxy-
pyrazol-4-yl)propionate 9b
Compound 5 (100 mg, 0.24 mmol) was dissolved in methanol
(10 ml) and 1  aqueous hydrochloric acid was added dropwise
to the solution until its UV spectrum showed the reaction to
be complete (ca. 1.5 equiv., 1  aqueous HCl was required).
Methylhydrazine (13 µl, 0.24 mmol) was added at room tem-
perature to the reaction mixture which was then stirred for a
further 30 h. After this the solvent was removed in vacuo
and the residue was dissolved in ethyl acetate. The solution was
washed consecutively with saturated aqueous sodium hydro-
gen carbonate, water and brine and then dried (Na2SO4).
The solvent was removed in vacuo to yield a yellow oil (75 mg;
75% overall). This was chromatographed on silica gel with
gradient elution from ethyl acetate to methanol–ethyl acetate
(1:4) to give the title compound 9b as a colourless gum, which
failed to crystallise (35 mg, 35%); [α]2D4 Ϫ8.3 (c 0.35, CHCl3)
(Found: C, 63.1; H, 5.6; N, 9.9. C22H23N3O5ؒ0.5H2O requires C,
63.2; H, 5.7; N, 10.05%) [Found: m/z (EI), 409.1634 ([M]ϩ).
C22H23N3O5 requires 409.1632]; νmax(CHCl3)/cmϪ1 1740sh and
OH), 1713 (urethane and ester) and 1605 (C᎐N); λmax(MeOH,
᎐
pH 7)/nm 225sh and 250 (ε 3800 and 2480); λmax(MeOH, pH
12)/nm 240 (ε 4540); λmax(MeOH, pH 2)/nm 231 (ε 4400);
δH (360 MHz, [2H6]-DMSO) 11–10 (2 H, br exch. s, NH/OH),
7.67 (1 H, br exch. d, JN H ,2 7.6, NH), 7.32 (10 H, s, 2 × PhCH2),
7.17 (1 H, s, H-3Ј), 5.10 and 5.00 (4 H, 2 × s, 2 × PhCH2), 4.20
(1 H, d × t, J2,N H = J2,3A = 8.5, J2,3B 5.7, H-2), 2.76 (1 H, d × d,
J3B.3A 14.6, J3B,2 5.7, H-3B) and 2.57 (1 H, d × d, J3A,3B 14.6, J3A,2
8.5, H-3A); δC(50.3 MHz, [2H6]-DMSO) 171.83 (ester), 159.28
(C-5Ј), 155.90 (urethane), 136.61 and 135.86 (2 × ipso), 129.25
(C-3Ј), 128.09–127.48 (aromatic), 98.36 (C-4Ј), 65.83 and 65.42
(2 × PhCH2), 54.71 (C-2) and 24.29 (C-3).
1719 (urethane and ester) and 1580 (C᎐N); λmax(MeOH, pH 7)/
᎐
nm 254 (ε 7500); λmax(MeOH, pH 12)/nm 244 (ε 7300); λmax
-
(MeOH, pH 2)/nm 233 (ε 6370); δH (360 MHz, [2H6]-DMSO)
7.90 (1 H, br exch. s, NH), 7.32 (10 H, s, ArH), 7.07 (1 H, s,
H-3Ј), 5.08 and 5.01 (4 H, 2 × s, 2 × PhCH2), 4.18 (1 H, br q,
J2,N H = J2,3A = J2,3B 7, H-2), 3.40 (3 H, s, N᎐CH3), 2.74 (1 H,
d × d, J3B,3A 14.6, J3B,2 5.7, H-3B) and 2.58 (1 H, d × d, J3A,3B
14.6, J3A,2 8.4, H-3A); δC(50.3 MHz, [2H6]-DMSO) 171.82
(ester), 155.96 (urethane), 153.5 (br) (C-5Ј), 136.69 and 135.90
(2 × ipso C), 136.54 (C-3Ј), 128.36–127.66 (aromatic), 97.57 (C-
4Ј), 65.88 and 65.46 (2 × PhCH2), 55.01 (C-2), 32.32 (N᎐CH3)
and 24.76 (C-3).
Benzyl (2S)-2-benzyloxycarbonylamino-3-(1-acetylpyrazol-4-
yl)propionate 12
Compound 9a (170 mg, 0.43 mmol) was dissolved in dry
acetonitrile (6 ml) and 4-dimethylaminopyridine (5.0 mg, 0.04
mmol) was added to the solution at room temperature under
nitrogen. After the mixture had been stirred for 5 min, acetic
anhydride (40 µl, 0.43 mmol) was added dropwise to it and stir-
ring continued at room temperature for 14 h. The fine white
suspended solid was filtered off and washed with cold aceto-
nitrile. Upon recrystallisation from ethyl acetate it yielded the
title compound 12 as white microcrystals (90 mg, 50%); mp
149–150 ЊC; [α]2D5 ϩ0.3 (c 0.325, CHCl3) (Found: C, 63.1; H, 5.2;
N, 9.5. C23H23N3O6 requires C, 63.2; H, 5.3; N, 9.6%) [Found:
m/z (EI) 437.1629 ([M]ϩ). C23H23N3O6 requires 437.1627];
νmax(KBr)/cmϪ1 3331 (NH, OH), 1734 and 1717 (urethane and
ester), 1692 (amide) and 1627 (pyrazol-5-one); λmax(MeOH, pH
7)/nm 270 and 290 (ε 2450 and 2080); λmax(MeOH, pH 12)/nm
238 and 297 (ε 1460 and 1900); λmax(MeOH, pH 2)/nm 231 and
264 (ε 1560 and 790); λmax(MeOH, pH 7)/nm 225sh and 293 (ε
2090 and 3770); λmax(MeOH, pH 12)/nm 239 and 296 (ε 3800
Benzyl (2S)-2-benzyloxycarbonylamino-3-(2-acetyl-1-methyl-5-
oxopyrazol-4-yl)propionate 10b
The pyrazole 9b (130 mg, 0.32 mmol) was dissolved in dry
acetonitrile (6 ml) with 4-dimethylaminopyridine (4 mg, 0.032
mmol) at room temperature under nitrogen. After the mixture
had been stirred for 20 min, acetic anhydride (30 µl, 0.32 mmol)
was added dropwise to it and stirring was continued for 15 h at
room temperature. The solvent was then removed in vacuo to
yield a pale brown oil (114 mg, 80%) which was chromato-
graphed on silica gel using hexane–ethyl acetate (1:4) as eluent.
The major product, the title compound 10b, was obtained as
a pale yellow oil (71 mg, 50%); [α]2D8 Ϫ1.3 (c 0.15, CHCl3)
(Found: C, 64.1; H, 5.65; N, 9.0. C24H25N3O6 requires C, 63.9;
H, 5.5; N, 9.3%) [Found: m/z (EI) 451.1740 ([M]ϩ). C24H25N3O6
requires 451.1737]; νmax(film)/cmϪ1 3320 (NH), 1740sh and 1720
1300
J. Chem. Soc., Perkin Trans. 1, 1997

View Article Online
and 2060); λmax(MeOH, pH 2)/nm 232 and 264 (ε 2720 and
4190); δH (360 MHz, [2H6]-DMSO) 11.27 (2 H, br exch. s, NH),
7.94 (1 H, s, H-3Ј), 7.86 (1 H, d, JN H ,2 8, NH), 7.31 (10 H, m,
ArH), 5.10 and 5.0 (4 H, 2 × s, 2 × PhCH2), 4.27 (1 H, br d × t,
J2,3A 9.5, J2,3B 5.6, J2,N H 8, H-2), 2.78 (1 H, d × d, J3A,3B 14.5,
J3B,2 5.6, H-3B), 2.69 (1 H, d × d, J3A,3B 14.5, J3A,2 9.5, H-3A)
and 2.42 (3 H, s, CH3CO); when the CH3CO protons (δ 2.42)
were irradiated, no enhancement was detected in H-3Ј (δ 7.94)
and when H-3Ј was irradiated, no enhancement was observed in
the CH3CO signal; δC(62.9 MHz, [2H6]-DMSO) 171.45 (ester),
167.50 (N᎐COCH3), 163.01 (C-5Ј), 156.01 (urethane), 136.82
and 135.77 (2 × ipso C), 128.37–127.61 (aromatic), 127.15
(C-3Ј), 109.64 (C-4Ј), 66.1 and 65.5 (2 × PhCH2), 53.42 (C-2),
24.07 (C-3) and 21.13 (N᎐COCH3).
Benzyl (2S)-2-benzyloxycarbonylamino-3-[5-hydroxy-1-(p-nitro-
phenyl)pyrazol-4-yl]propionate 9d
Compound 5 (300 mg, 0.74 mmol) was dissolved in methanol
(10 ml) and 1  aqueous hydrochloric acid was added dropwise
to the solution until its UV spectrum showed reaction to be
complete (ca. 1.5 equiv. was required). 4-Nitrophenylhydrazine
(112 mg, 0.74 mmol) and sodium acetate (100 mg, 1.2 mmol)
were added at room temperature to the mixture which was then
stirred for 18 h at room temperature. The resulting brown solid
was filtered off, washed with cold methanol and recrystallised
from methanol to yield pale brown needles (138 mg, 36%);
mp 175–177 ЊC; [α]2D4 ϩ11.5 (c 0.357, CHCl3) (Found: C, 62.5;
H, 4.4; N, 10.7. C27H24N4O7 requires C, 62.8; H, 4.65; N,
10.85%); m/z [ϩve FAB (3-NBA, xenon)] 517 ([M ϩ H]ϩ);
νmax(KBr)/cmϪ1 3322 (NH), 1738 (urethane and ester), 1683
and 1637 (pyrazolone); λmax(MeOH, pH 7)/nm 327 (ε 7800);
λmax(MeOH, pH 12)/nm 338 (ε 9340); λmax(MeOH, pH 2)/
nm 318 (ε 7300); δH (360 MHz, [2H6]-DMSO) 11.8 (2 H, br,
NH2), 8.32 (2 H, d, J 9.3, ArH), 8.06 (2 H, d, J 9.3, ArH),
7.88 (1 H, exch. d, JN H ,2 7.9, NH), 7.55 (1 H, s, H-3Ј), 7.31 (10
H, m, aromatic), 5.11 (2 H, s, PhCH2), 5.02 (2 H, AB, PhCH2),
4.29 (1 H, d × d × d, J2,3A 9.1, J2,N H 7.9, J2,3R 5.8, H-2), 2.84 (1
H, d × d, J3B,3A 14.7, J3B,2 5.8, H-3B) and 2.69 (1 H, d × d, J3A,3B
14.7, J3A,2 9.1, H-3A); δC(62.9 MHz, [2H6]-DMSO) 171.82
(ester), 156.04 (urethane), 143.6, 142.13, 136.90 and 135.85
(4 × ipso C), 128.4–119.29 (aromatic), ~100.0 (C-4Ј), 66.10 and
65.56 (2 × PhCH2), 54.25 (C-2) and 24.41 (C-3).
Benzyl (2S)-2-benzyloxycarbonylamino-3-(5-hydroxy-1-phenyl-
pyrazol-4-yl)propionate 9c
Compound 5 (150 mg, 0.37 mmol) was dissolved in methanol
(10 ml) and 1  aqueous hydrochloric acid was added drop-
wise to the solution until its UV spectrum showed the reaction
to be complete (ca. 1.5 equiv. was required). Phenylhydrazine
hydrochloride (54 mg, 0.37 mmol) and sodium acetate (50 mg,
0.60 mmol) were added to the reaction mixture which was then
stirred for 3 days at room temperature. After this the solvent was
removed in vacuo and the residue was dissolved in chloro-
form. The solution was washed twice with water and once with
brine and dried (Na2SO4). The solvent was removed in vacuo to
yield a brown foam (140 mg, 80% overall) which was chromato-
graphed on silica gel using ethyl acetate–dichloromethane
(3:7). The major product, the title compound 9c, was isolated
as a solid and was recrystallised from ethyl acetate–hexane to
give off-white crystals (70 mg, 40%); mp 126–128 ЊC; [α]2D6 ϩ2.0
(c 0.35, CHCl3) (Found: C, 68.5; H, 5.3; N, 8.6. C27H25N3O5
requires C, 68.8; H, 5.3; N, 8.9%); m/z [ϩve FAB (3-NBA)] 494
([M ϩ Na]ϩ) and 472 ([M ϩ H]ϩ); νmax(CHCl3)/cmϪ1 1740sh
and 1719 (urethane and ester); λmax(MeOH, pH 7)/nm 247
and 275sh (ε 6960 and 2830); δH (360 MHz, [2H6]-DMSO)
11.0 (1 H, br exch. s, OH), 7.93 (1 H, br exch. s, NH), 7.70–
7.20 (16 H, m, ArH), 5.10 and 5.02 (4 H, 2 × s, 2 × PhCH2),
4.27 (1 H, br q, J ca. 7, H-2), 2.83 (1 H, d × d, J3B,3A 14.6,
J3B,2 5.6, H-3B) and 2.68 (1 H, d × d, J3A,3B 14.6, J3A,2 9.0, H-
3A); δC(50.3 MHz, [2H6]-DMSO) 171.31 (ester), 156.60
(urethane), 139.56, 137.21 and 136.17 (3 × ipso C), 138.0–
121.0 (aromatics), 100.0 (C-4Ј), 66.62 and 66.11 (2 × PhCH2),
54.90 (C-2) and 25.08 (C-3).
Benzyl (2S)-2-benzyloxycarbonylamino-3-[2-acetyl-1-(p-nitro-
phenyl)-5-oxopyrazol-4-yl]propionate 10d
The pyrazole 9d (77 mg, 0.15 mmol) was dissolved in dry
acetonitrile (4 ml) and 4-dimethylaminopyridine (3 mg, 0.02
mmol) was added to the solution at room temperature, under
nitrogen. After the mixture had been stirred for 10 min, acetic
anhydride (14 µl, 0.15 mmol) was added dropwise to it and
stirring continued for 14 h at room temperature. Further
acetic anhydride (5 µl, 0.05 mmol) was added to the mixture and,
after a total of 20 h, the solvent was removed in vacuo. The
resulting brown residue (85 mg) was chromatographed on silica
gel using gradient elution from ethyl acetate–dichloromethane
(1:9) to ethyl acetate–dichloromethane (2:3). A minor product
was eluted as a gum using ethyl acetate–dichloromethane
(1:9), followed by a more polar major product, eluted using
ethyl acetate–dichloromethane (1:4). The minor product
benzyl (2S)-2-benzyloxycarbonylamino-3-[5-acetoxy-1-(p-nitro-
phenyl)pyrazol-4-yl]propionate 14 (10 mg, 12%); m/z (EI) 516
([M Ϫ CH3CO]ϩ); δH (360 MHz, C2HCl3) 8.3 (2 H, d, J 9.0,
ArH), 7.69 (2 H, d, J 9.2, ArH), 7.34 (11 H, m, ArH), 5.48 (1 H,
exch. d, JN H ,2 7.3, NH), 5.19 (2 H, AB, JAB 12.1, PhCH2), 5.12 (2
H, AB, JAB 12.2, PhCH2), 4.63 (1 H, q, J ca. 5.8, H-2), 2.93 (2
H, m, overlapping AB systems, J3B,3A 14.9, J3B,2 = J3A,2 5.8,
2 × H-3) and 2.19 (3 H, s, N᎐COCH3). The major product was
the title compound 10d (45 mg, 54%); m/z [ϩve FAB (3-NBA)]
559 [M ϩ H]ϩ; νmax(CHCl3)/cmϪ1 1720 (urethane and ester) and
1656 (amide and pyrazolone); λmax(MeOH, pH 7)/nm 285 and
312 (ε 15 700 and 14 400); λmax(MeOH, pH 12)/nm 337 (ε
18 560); λmax(MeOH, pH 2)/nm 318 (ε 15 000); δH (360 MHz,
C2HCl3) 8.26 (2 H, d, J 9.2, ArH), 7.76 (1 H, s, H-3Ј), 7.34 (12
H, m, ArH), 6.01 (1 H, exch. d, JN H ,2 7.7, NH), 5.17 (2 H, AB,
JAB 11.9, PhCH2), 5.09 (2 H, AB, JAB 12.2, PhCH2), 4.65 (1 H,
br q, J ca. 7, H-2), 2.96 (1 H, d × d, J3B,3A 15.5, J3B,2 5.1, H-3B),
2.85 (1 H, d × d, J3A,3B 15.5, J3A,2 7, H-3A) and 2.21 (3 H, s,
N᎐COCH3). Irradiation of H-3Ј (δ 7.76) produced an
enhancement of 10% in COCH3 (δ 2.21). Irradiation of
COCH3, produced an enhancement of 15% in H-3Ј; δC(62.9
MHz, [2H6]-DMSO) 171.21 (ester), 166.0 (N–COCH3), 164.52
(C-5Ј), 155.95 (urethane), 144.46, 142.65, 141.24, 136.76 and
135.70 (4 × ipso C and C-3Ј), 128.37–122.49 (aromatic), 109.87
(C-4Ј), 66.28 and 65.63 (2 × PhCH2), 52.47 (C-2), 24.76 (C-3)
and 21.43 (N–COCH3).
Benzyl (2S,4RS)-1-benzyloxycarbonyl-4-(p-nitrophenyl)-
hydrazonomethylpyroglutamate 13d
Compound 5 (200 mg, 0.49 mmol) was dissolved in methanol
(10 ml) and 1  aqueous hydrochloric acid was added dropwise
to the solution until its UV spectrum showed reaction to be
complete (ca. 1.5 equiv. was required). 4-Nitrophenylhydrazine
(75 mg, 0.49 mmol) was added to the reaction mixture which
was then stirred for 4 h at room temperature. The resulting
yellow solid was filtered off, washed with cold methanol and
recrystallised from methanol to afford yellow needles (120 mg,
50%); mp 134–135 ЊC; [α]2D8 0.0 (c 0.31, CHCl3) (Found: C, 62.8;
H, 4.5; N, 10.8. C27H24N4O7 requires C, 62.8; H, 4.65; N,
10.85%); m/z [ϩve FAB (3-NBA)] 517 ([M ϩ H]ϩ); νmax(KBr)/
cmϪ1 3295 (NH), 1790 and 1734 (urethane and ester) and 1595
(C᎐N); λmax(MeOH, pH 7)/nm 376 (ε 10 500); λmax(MeOH, pH
᎐
12)/nm 340 (ε 7990); λmax(MeOH, pH 2)/nm 324 (ε 6000);
δH (360 MHz, C2HCl3) 8.94 (1 H, exch. s, NH), 8.06 (2 H, d, J3Ј,2Ј
9.1, ArH), 7.40 (1 H, d, J6,4 4.2, H-6), 7.32 (10 H, m, ArH), 6.97
(2 H, d, J2Ј,3Ј 9.1, ArH), 5.20 and 5.16 (4 H, 2 × s, 2 × PhCH2),
4.79 (1 H, d, J2,3S 8.7, H-2), 3.68 (1 H, d × d × d, J4,3S 10.0, J4,3R
9, J4,6 4.2, H-4), 2.72 (1 H, d × t, J3S,3R 13.4, J3S,2 = J3S,4 10,
H-3S) and 2.38 (1 H, d × d, J3R,3S 13.4, J3R,4 9, H-3R). Irradi-
ation of H-2 (δ 4.79) produced an enhancement of 4% in H-3S
(δ 2.72). Irradiation of H-4 (δ 3.68) produced an enhancement
of 2.5% in H-3R (δ 2.38).
J. Chem. Soc., Perkin Trans. 1, 1997
1301

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Benzyl (2S,4RS)-1-benzyloxycarbonyl-4-(2,4-dinitrophenyl)-
hydrazonomethylpyroglutamate 13e
and 5.14 (4 H, 2 × s, 2 × PhCH2), 4.73 (1 H, d × d, J2,3S 9.8, J2,3R
6.3, H-2), 4.55 (1 H, s, H-6), 3.30 and 3.26 [6 H, 2 × s,
C(OCH3)2], 2.41 (1 H, d × d, J3S,3R 13.0, J3S,2 9.8, H-3S) and
Compound 5 (100 mg, 0.24 mmol) was dissolved in methanol
(10 ml) and 1  aqueous hydrochloric acid was added dropwise
to the solution until its UV spectrum showed reaction to be
complete (ca. 1.5 equiv. was required). 2,4-Dinitrophenyl-
hydrazine (76 mg, 0.35 mmol) and sodium acetate (20 mg, 0.24
mmol) were added to the reaction mixture which was then
stirred for 5 h at room temperature. The resulting yellow solid
was filtered off, washed with cold methanol and recrystallised
2
2.01 (1 H, overlapped by major isomer, H-3R). The H NMR
spectrum (38.4 MHz) showed a deuterium signal at δ 3.0. The
1H decoupled 13C NMR spectrum showed the C-4 signal as a
pair of triplets at δ 46.8 and 47.6.
Benzyl (2S)-2-benzyloxycarbonylamino-3-(5-hydroxyisoxazol-4-
yl)propionate 16
1
Benzyl
(2S,4RS)-N-benzyloxycarbonyl-4-formylpyrogluta-
from ethanol to afford yellow needles. H NMR Spectroscopy
mate 6 was prepared as above by hydrolysis of the enaminone
5 (204 mg, 0.5 mmol). Hydroxylamine hydrochloride (35 mg,
0.51 mmol) was added to the methanolic solution of crude
aldehyde 6 at room temperature, followed by sodium acetate
(17.0 mg, 0.2 mmol), added to buffer the mixture to pH 5–6.
The mixture was stirred at room temperature for 15 h after
which the solvent was removed in vacuo. The residue was par-
titioned between chloroform and water and the organic phase
was separated and washed to neutrality with water and brine
and then dried (MgSO4). The solvent was removed in vacuo to
afford a pale yellow gum (160 mg, 81%); m/z (EI) 396 ([M]ϩ);
m/z [FAB] 419 ([M ϩ Na]ϩ); νmax(film)/cmϪ1 1790w and 1720s
(ester); δH (360 MHz, C2HCl3, unstable with time) 7.47 (ca. 1 H,
s, H-3Ј), 7.3 (ca. 10 H, ArH), 6.03 (ca. 1 H, d, J 8, NH), 5.1 (ca.
4 H, m, 2 × PhCH2), 4.5 (ca. 1 H, m, H-2) and 2.7 (ca. 2 H, m,
H-3).
showed, by integration of the H-4 resonances, the presence of a
2:1 mixture of diastereoisomers. These isomers could not be
separated by further recrystallisation (93 mg, 70%), mp 126–
128 ЊC; [α]2D8 ϩ5.8 (c 0.33, CHCl3) (Found: C, 57.7; H, 4.1; N,
12.3. C27H23N5O9 requires C, 57.75; H, 4.1; N, 12.5%); m/z
[ϩve FAB (3-NBA)] 584 ([M ϩ Na]ϩ) and 562 ([M ϩ H]ϩ);
νmax(KBr)/cmϪ1 1796 and 1742 (urethane and ester);
λmax(MeOH)/nm 348 (ε 8060); δH (360 MHz, C2HCl3, major
isomer) 11.10 (1 H, exch. s, NH), 9.11 (1 H, d, J 2.5, ArH),
8.30 (1 H, d × d, J 9.5, 2.5, ArH), 7.85 (1 H, d, J 9.5, ArH),
7.66 (1 H, d, J6,4 4.3, H-6), 7.50–7.20 (10 H, m, ArH), 5.24
and 5.18 (4 H, 2 × s, PhCH2), 4.82 (1 H, d × d, J2,3S 9.6, J2,3R
1.2, H-2), 3.81 (1 H, d × d × d, J4,3S 11.7, J4,3R 8.6, J4,6 4.3,
H-4), 2.74 (1 H, m, overlapping with minor isomer, H-3S) and
2.45 (1 H, d × d × d, J3R,3S 13.6, J3R,4 8.6, J3R,2 1.2, H-3R);
δH (360 MHz, C2HCl3, minor isomer) 11.3 (1 H, exch. s, NH),
9.09 (1 H, d, J 2.5, ArH), 8.22 (1 H, d × d, J 9.5, 2.5, ArH),
7.76 (1 H, d, J 9.5, ArH), 7.54 (1 H, d, J6,4 4.2, H-6), 7.50–
7.20 (10 H, m, ArH), 5.23 (2 H, s, PhCH2), 5.05 (2 H, AB,
JAB 12.3, PhCH2), 4.79 (1 H, d × d, J2,3S 9.1, J2,3R 5.5, H-2),
3.71 (1 H, d × t, J4,3S = J4,3R 6.0, J4,6 4.2, H-4), 2.74 (1 H, m,
overlapping with major isomer, H-3S) and 2.59 (1 H, d × t,
J3R,3S 11.9, J ca. 6, H-3R).
Benzyl (2S)-2-benzyloxycarbonylamino-3-(5-acetoxyisoxazol-4-
yl)propionate 18
The crude reaction product from the above reaction (70 mg,
0.18 mmol) was dissolved in dry acetonitrile (3 ml) with
4-dimethylaminopyridine (2.5 mg, 0.02 mmol) at room tem-
perature under nitrogen. After being stirred for 10 min, the
reaction mixture was treated with acetic anhydride (17 µl, 0.18
mmol), added dropwise and then stirred at room temperature
for 2 h. The solvent was removed in vacuo to yield an orange
gum (70 mg, 88%) which was chromatographed on silica gel
using ethyl acetate in dichloromethane (1:9) to afford a colour-
less oil which could not be crystallised (35 mg, 45%); [α]2D9 ϩ8.6
(c 0.233, CHCl3); m/z [ϩve FAB (3-NBA)] 461 ([M ϩ Na]ϩ)
and 439 ([M ϩ H]ϩ); νmax(CHCl3)/cmϪ1 1771 (enol acetate) and
1724 (urethane and ester); λmax(MeOH, pH 7)/nm 285 (ε
10 680); λmax(MeOH, pH 12)/nm 256 (ε 7300); λmax(MeOH, pH
2)/nm 263 (ε 6860); δH (200 MHz, C2HCl3) 8.08 (1 H, s, H-3Ј),
7.35 (10 H, m, ArH), 5.67 (1 H, br exch. d, JN H ,2 6, NH), 5.17
and 5.11 (4 H, 2 × s, 2 × PhCH2), 4.61 (1 H, br q, J ca. 6, H-2),
2.89 (1 H, d × d, J3B,3A 15, J3B,2 5.5, H-3B), 2.79 (1 H, d × d,
J3A,3B 15, J3A,2 6.1, H-3A) and 2.35 (3 H, s, CH3CO); irradiation
of 3Ј-CH (δ 2.35) led to no detectable enhancement in CH3CO
(δ 2.35) and similarly, irradiation of CH3CO led to no detect-
able enhancement in 3Ј-CH; δC(50.3 MHz, [2H6]-DMSO)
171.46 (ester), 167.94 (O–COCH3), 156.51 (urethane), 142.78
and 142.67 (C-3Ј and C-5Ј), 137.26 and 136.20 (2 × ipso C),
128.91–128.21 (aromatic), 103.82 (C-4Ј), 66.89 and 66.19
(2 × PhCH2), 52.91 (C-2), 24.57 (C-3) and 20.98 (O–COCH3).
Assessment of stereochemical integrity during the ring-switching
process
Compound 5 (204 mg, 0.5 mmol) was dissolved in methan-
[2H1]ol (8 ml) and hydrolysed by the dropwise addition of 20%
2
2HCl in H2O. Complete hydrolysis was confirmed by UV spec-
troscopy after which hydrazine hydrate (22 µl, 0.45 mmol) was
added to the solution; it was then stirred for 15 h at room
temperature. TLC was indicative of the presence of a substan-
tial amount of unchanged aldehyde 6. Sodium acetate (250 mg,
3.0 mmol) was added to buffer the reaction mixture to pH 5–6
and, after 3 h, the solvent was removed in vacuo and the residue
was partitioned between deuterium oxide and deuteriochloro-
form. The layers were separated and the organic phase was
washed to neutrality with deuterium oxide and dried (Na2SO4)
and then the solvent was removed in vacuo to yield a viscous
yellow oil (190 mg, 90%) which was chromatographed on silica
gel using a gradient elution from hexane–ethyl acetate (1:9) to
methanol–ethyl acetate (1:9). The major product was eluted
immediately, after which the more polar minor product was
1
eluted as a broad band. The H NMR spectrum of the minor
product (40 mg, 20%) was identical with that of compound 11
2
obtained in the analogous reaction in MeOH, and H NMR
Benzyl (2S,4RS)-1-benzyloxycarbonyl-4-benzyloxyimino-
methylpyroglutamate 17
spectroscopy confirmed that deuterium had not been incorpor-
ated. The major product (70 mg, 33%) was shown by inte-
gration of the 2-CH resonances in the 1H NMR spectrum to be
a 3:1 mixture of diastereoisomers of the acetal 15; [α]2D3 Ϫ45.8
Compound 6 was generated in situ by hydrolysis of the enami-
none 5 (102 mg, 0.25 mmol) as described above. O-Benzyl-
hydroxylamine hydrochloride (40 mg, 0.25 mmol) in methanol
(1 ml) was added to it at pH 1 and the mixture was stirred at
room temperature for 20 h. After this the solvent was removed
in vacuo and the residue was partitioned between chloroform (3
ml) and saturated aqueous sodium hydrogen carbonate (2 ml).
The organic phase was separated and washed with water and
brine and then dried (Na2SO4). The solvent was removed in
vacuo to afford a yellow oil (98%), [α]2D6 Ϫ11.9 (c 0.547, CHCl3).
This was further purified by chromatography on silica gel using
dichloromethane as eluent, to give a pale yellow gum (75 mg,
2
(c 0.6, MeOH) [Found: m/z (EI) 428.1689 ([M]ϩ). C23H24NO7 H
requires 428.1685]; νmax(CHCl3)/cmϪ1 1796, 1750 and 1730
(urethane and ester); δH (360 MHz, [2H6]-DMSO, major
diastereoisomer) 7.36 (10 H, m, ArH), 5.19 (2 H, AB, JAB 10.0,
PhCH2), 5.14 (2 H, s, PhCH2), 4.78 (1 H, d × d, J2,3S 10, J2,3R
2.2, H-2), 4.63 (1 H, s, H-6), 3.34 and 3.33 [6 H, 2 × s,
C(OCH3)2], 2.44 (1 H, d × d, J3S,3R 13.4, J3S,2 10.0, H-3S) and
2.01 (1 H, d × d, J3R,3S 13.4, J3R,2 2.2, H-3R); δH (360 MHz,
[2H6]-DMSO, minor diastereoisomer) 7.36 (10 H, m, ArH), 5.19
1302
J. Chem. Soc., Perkin Trans. 1, 1997

View Article Online
62%) (Found: C, 68.8; H, 5.3; N, 5.5. C28H26N2O6 requires C,
69.1; H, 5.35; N, 5.8%); m/z [ϩve FAB (thioglycerol)] 487
([M ϩ H]ϩ) and 509 ([M ϩ Na]ϩ); νmax(CHCl3)/cmϪ1 1799
(imide) and 1752 (ester); δH (360 MHz, C2HCl3) 7.57 (d, J6,4 4.9,
H-6 syn, trans), 7.52 (d, J6,4 5.0, H-6 syn, cis), 7.34 (10 H, m,
ArH), 6.90 (d, J6,4 5.1, H-6 anti, trans), 6.88 (d, J6,4 5.3, H-6 anti,
cis) (the four peaks for H-6 integrated as a total of 1 H), 5.23–
5.03 (4 H, m, 2 × PhCH2), 4.73–4.67 (1 H, m, H-2), 3.88, 3.56
and 3.48 (1 H, 3 × m, H-4), 2.75, 2.54, 2.35, 2.29, 2.21 and 1.95
(1 H, 6 × m, 3-CH2).
added to glacial acetic acid (5 ml) and activated under an
atmosphere of hydrogen. After ca. 5 min compound 9b (204
mg, 0.5 mmol) was added to the mixture as a solution in glacial
acetic acid (2 ml). The reaction mixture was vigorously stirred
at room temperature under hydrogen for 22 h after which it was
filtered through Celite and the solvent was removed in vacuo to
afford a brown gum. This was dissolved in water and the solu-
tion washed twice with ethyl acetate. The aqueous phase was
lyophilised repeatedly until all of the acetic acid had been
removed. This gave the title acid 20b as a hygroscopic pink foam
(60 mg, 70%); [α]2D5 Ϫ55.5 (c 0.51, CHCl3) [Found: m/z (EI)
185.0800 ([M]ϩ). C7H11N3O3 requires 185.0799]; νmax(KBr)/
cmϪ1 3600–2600br (OH, NH) and 1597 (CO of amino acid);
λmax(MeOH, pH 7)/nm 252 (ε 5400); λmax(MeOH, pH
12)/nm 243 (ε 6220); λmax(MeOH, pH 2)/nm 234 (ε 5000);
δH (360 MHz, [2H6]-DMSO) 7.10 (1 H, s, H-3Ј), 3.39 (1 H, t,
partially obscured by N–Me, J2,3A = J2,3B = 5.5, H-2), 3.37
(3 H, s, N–CH3), 2.70 (1 H, d × d, J3A,3B 15.5, J3A,2 5.5,
H-3A) and 2.59 (1 H, d × d, J3B,3A 15.5, J3B,2 5, H-3B);
δC(62.9 MHz, [2H6]-DMSO) 171.82 (CO2H), 152.53 (C-5Ј),
137.42 (C-3Ј), 94.37 (C-4Ј), 54.71 (C-2), 32.89 (N–CH3) and
25.76 (C-3).
(2S)-2-Amino-3-(5-hydroxypyrazol-4-yl)propionic acid 20a and
(2S)-2-benzyloxycarbonylamino-3-(5-hydroxypyrazol-4-yl)-
propionic acid 21
Method A. Compound 9a (200 mg, 0.50 mmol) was dissolved
in methanol–water (9:1; 5 ml) containing 10% palladium-on-
charcoal (20 mg). The system was purged with hydrogen and
stirred vigorously under an atmosphere of hydrogen, at room
temperature, for 3 days. After this time, the reaction was filtered
through Celite and the catalyst was washed with methanol.
Removal of the solvent from the combined filtrate and wash-
ings in vacuo afforded a brown oil which was dissolved in water
and the solution washed twice with chloroform. The aqueous
1
phase was lyophilised to a fine solid (70 mg), the H NMR
tert-Butyl (2S)-N-tert-butoxycarbonyl-4-methoxymethylene-
spectrum of which showed two major products to be present.
These were separated by preparative reverse phase HPLC
[ZORBAX C8 column (21.2 mm × 25 cm)] using water as
eluent. Both products were obtained as hygroscopic lyophilates.
The title acid 20a (18 mg, 20%); [α]2D4 Ϫ37.7 (c 0.48, H2O)
[Found: m/z (EI) 171.0643 ([M]ϩ). C6H9N3O3 requires
171.0641]; νmax(KBr)/cmϪ1 3600–2800br (NH, OH) and 1607br
(CO2H); λmax(MeOH, pH 7)/nm 231 and 247 (ε 3700 and 3800);
λmax(MeOH, pH 12)/nm 238 (ε 5690); λmax(MeOH, pH 2)/nm
231 (ε 5130); δH (360 MHz, [2H6]-DMSO) 9.7–8.7 (3 H, br, exch.
s, NH, OH), 7.15 (1 H, s, H-3Ј), 3.38 (1 H, d × d, J2,3A 6, J2,3B
4.3, H-2), 2.68 (2 H, overlapping AB system, J3B,3A 15.3, J3A,2 6,
J3B,2 4.3, 3-CH2); δC(62.9 MHz [2H6]-DMSO) 171.4 (C–CO2H),
159.11 (C-5Ј), 130.85 (C-3Ј), 98.24 (C-4Ј), 54.62 (C-2) and 24.79
(C-3). The second product proved to be the title acid 21 (15 mg,
10%); [Found: m/z (EI) 287.0906 ([M Ϫ H2O]ϩ). C14H13N3O4
requires 287.0904]; m/z [ϩve FAB (thioglycerol)] 328 ([M ϩ
Na]ϩ) and 306 ([M ϩ H]ϩ); νmax(KBr)/cmϪ1 1721 (urethane) and
1622 (acid); λmax(MeOH, pH 7)/nm 225sh and 250sh (ε 1500
and 1000); λmax(MeOH, pH 12)/nm 240 (ε 3470); λmax(MeOH,
pH 2)/nm 230 (ε 3450); δH (360 MHz, [2H6]-DMSO) 12.0–11.0
(variable integration, br, exch. s, OH, NH), 7.41 (1 H, d, JN H ,2
8.1, NH), 7.32 (5 H, m, ArH), 7.18 (1 H, s, H-3Ј), 4.99 (1 H, AB,
JAB 12.4, PhCH2), 4.03 (1 H, d × t, J2,N H = J2,3A = 9.1, J2,3B 4.8,
H-2), 2.72 (1 H, d × d, J3B,3A 15, J3B,2 4.8, H-3B) and 2.54 (1 H,
d × d, J3A,3B 15, J3A,2 9.1, H-3A); δC(62.9 MHz, [2H6]-DMSO)
173.55 (C–CO2), 159.14 (C-5Ј), 155.90 (urethane), 137.01 (ipso
C), 129.03 (C-3Ј), 128.33–127.60 (aromatic), 98.99 (C-4Ј), 65.29
(PhCH2), 54.62 (C-2) and 24.40 (C-3).
Method B. Platinum() oxide monohydrate (Adam’s
catalyst) (25 mg) was added to glacial acetic acid (5 ml) and
activated under an atmosphere of hydrogen. After ca. 5 min
compound 9a (210 mg, 0.53 mmol) was added to the reaction
mixture in such a way as to maintain the hydrogen atmosphere.
The reaction was vigorously stirred at room temperature for
22 h after which it was filtered through Celite to remove the
catalyst and the solvent was removed in vacuo. The residue was
dissolved in water and the aqueous solution was washed twice
with chloroform. The aqueous phase was lyophilised to con-
stant weight (58 mg, 65%). The product, the acid 20a, had
spectra identical with those obtained for the major product
using method A.
pyroglutamate 25
tert-Butyl
(2S)-1-tert-butoxycarbonyl-4-N-dimethylamino-
methylenepyroglutamate 2325 (10 g, 0.0294 mol) and screened
Methyl Orange (2 drops) were dissolved in methanol (100 ml)
with stirring. Aqueous 1  hydrochloric acid (ca. 32 ml
required) was added dropwise to the mixture at room tem-
perature at such a rate as to keep the pH of the solution at or
above the neutral point of the indicator. This took 40 min. The
solution was then concentrated to a small volume in vacuo,
diluted with water (15 ml) and extracted with ethyl acetate
(3 × 30 ml). The combined organic phases were washed with
brine, dried (MgSO4) and the solvent was removed in vacuo to
yield a yellow oil which was dissolved in a mixture of dichloro-
methane (10 ml) and diethyl ether (20 ml). The solution was
cooled to ice-bath temperature with stirring. Diazomethane
was prepared by dropwise addition of Diazald (21.4 g, 0.1 mol)
in diethyl ether (30 ml) into ethanol (15 ml) containing potas-
sium hydroxide (6 g) with stirring and heating to 60 ЊC to allow
its distillation into the solution. The reaction mixture was left
for 18 h at Ϫ18 ЊC after which the solvent and remaining diazo-
methane were removed by a stream of nitrogen. The resultant
yellow solid was recrystallised from ethyl acetate–light petrol-
eum (bp 60–80 ЊC) to yield the title compound 25 as fine needles
(5.74 g, 60%), mp 96–99 ЊC. The mother liquors were concen-
trated to a small volume in vacuo and purified by chrom-
atography on silica gel, eluting with dichloromethane–
methanol (96:4) to yield further product (1.4 g, 14%). An ana-
lytical sample was recrystallised from ethyl acetate–light petrol-
eum (bp 60–80%); mp 98–99 ЊC; [α]2D3 Ϫ17.7 (c 1.1, CHCl3)
(Found: C, 58.7; H, 8.0; N, 4.3. C16H25NO6 requires C, 58.7; H,
7.7; N, 4.3%); m/z (ϩve FAB, 3-NBA) 677 ([2M ϩ Na]ϩ), 350
([M ϩ Na]ϩ) and 328 ([M ϩ H]ϩ); νmax(KBr)/cmϪ1 1759
(urethane), 1747 (ester), 1698 and 1674 (urethane); λmax(MeOH,
pH 7)/nm 263 (log ε 4.02); δH (360 MHz, C2HCl3) 7.21 (1 H, t,
J6,3 2.5, H-6), 4.45 (1 H, d × d, J2,3A 3.6, J2,3B 10.5, H-2), 3.84 (3
H, s, OCH3), 2.88 (1 H, d × d × d, J3B,6 2.5, J3B,2 10.5, J3B,3A 17,
H-3B), 2.52 (1 H, J3A,6 2.5, J3A,2 3.6, J3A,3B 17, H-3A), 1.51 [9 H,
s, C(CH3)3] and 1.47 [9 H, s, C(CH3)3]; δC(125.76 MHz,
C2HCl3) 170.31 and 167.61 (2 × CO), 155.16 (HCO), 149.72
(urethane), 106.42 (C-4), 82.71 and 81.85 [2 × C(CH3)3], 61.68
(OCH3), 56.61 (C-2), 27.83 and 27.77 [2 × C(CH3)3] and 23.68
(C-3).
(2S)-2-Amino-3-(1-methyl-5-hydroxypyrazol-4-yl)propionic acid
20b
tert-Butyl (2S)-2-tert-butoxycarbonylamino-3-(2-methyl-4-oxo-
pyrimidin-5-yl)propionate 26b
Platinum() oxide monohydrate (Adam’s catalyst) (25 mg) was
Compound 25 (1.057 g, 3.23 mmol), acetamidine hydrochloride
J. Chem. Soc., Perkin Trans. 1, 1997
1303

View Article Online
(1.23 g, 13 mmol) and potassium carbonate (1.78 g, 13 mmol)
were heated in ethanol (30 ml) at reflux for 70 h. The solvent
was removed in vacuo and the resultant oil was partitioned
between 5% aqueous citric acid (30 ml) and dichloromethane
(20 ml). The aqueous phase was separated and extracted with
dichloromethane (2 × 20 ml). The combined organic phases
were washed with brine, dried (MgSO4) and the solvent was
removed in vacuo to yield a pale yellow oil which solidified when
stored. This was purified by chromatography on silica gel, elut-
ing with ethyl acetate–acetic acid (98:2) to give the title com-
pound 26b as a white solid (0.99 g, 87%). An analytical sample
was recrystallised [toluene–light petroleum (bp 60–80 ЊC)], mp
128–130 ЊC; [α]2D3 Ϫ39.5 (c 0.5, CHCl3) (Found: C, 58.0; H, 7.6;
N, 11.7. C17H27N3O5 requires C, 57.8; H, 7.7; N, 11.9%); m/z
[ϩve FAB, 3-NBA] 707 ([2M ϩ H]ϩ) and 354 ([M ϩ H]ϩ);
νmax(KBr)/cmϪ1 1710 (ester) and 1693 (urethane); λmax(MeOH)/
nm 226 and 276 (log ε 3.77 and 3.72); λmax(MeOH, pH 1)/nm
230 and 263 (log ε 3.84 and 3.66); δH (360 MHz, C2HCl3) 11.5
(1 H, br exch., NH), 7.81 (1 H, s, H-4Ј), 6.05 (1 H, exch. d,
JN H ,2 7.7, NH), 4.41 (1 H, m, H-2), 2.93 (1 H, d × d, J3A,2 3.7,
J3A,3B 14, H-3A), 2.76 (1 H, d × d, J3B,2 8.1, J3B,3A 14, H-3B),
2.47 (3 H, s, CH3), 1.39 [9 H, s, C(CH3)3] and 1.36 [9 H, s,
C(CH3)3]; addition of 2H2O caused the multiplet at δ 4.41 to
simplify. A minor component was evident in the 1H NMR
spectrum (~20% by integration); distinct peaks associated
with this occurred at δ 6.2 (br exch. d) and 4.25 (br m) but
when the spectrum was recorded in [2H6]-DMSO at 352 K,
peaks associated with the minor component were seen to
have coalesced with those of the major component; δC(125.76
MHz, C2HCl3) 170.71 and 165.76 (2 × CO), 158.36 (C-2Ј),
155.38 (urethane), 154.99 (C-4Ј), 120.95 (C-5Ј), 81.59 and
79.48 [2 × C(CH3)3], 54.03 (C-2), 30.52 (C-3), 28.28 and 28.00
[2 × C(CH3)3] and 21.45 (CH3).
11.5 mmol) and potassium carbonate (0.79 g, 0.57 mmol) were
heated in ethanol (30 ml) at reflux for 70 h. The solvent was
removed in vacuo and the resultant oil was partitioned
between ethyl acetate (20 ml) and water (20 ml). The aqueous
phase was separated and washed with ethyl acetate (2 × 20 ml).
The combined organic phases were washed with 5% aqueous
citric acid and brine, dried (MgSO4) and the solvent was
removed in vacuo to yield a tan coloured oil. This was purified
by chromatography on silica gel, eluting with dichloromethane–
methanol (91:9) to yield the title compound 26a as a tan
coloured foam (0.743 g, 76%); [α]2D3 Ϫ19.7 (c 2.6, CHCl3)
[Found: m/z (EI) 339.180 96. C16H25N3O5 requires 339.179 42];
νmax(film)/cmϪ1 1712 (ester) and 1672 (urethane); λmax(MeOH,
pH 7)/nm 224 and 273 (log ε 3.65 and 3.57); λmax(MeOH, pH
12)/nm 235 and 273 (log ε 3.71 and 3.57); λmax(MeOH, pH 1)/
nm 229 and 266 (log ε 3.71 and 2.52); δH (360 MHz, [2H6]-
DMSO) 12.55 (1 H, br exch., NH), 8.08 (1 H, s, CH), 7.74 (1 H,
s, CH), 7.12 (1 H, exch. d, JN H ,2 8, NH), 4.01 (1 H, m, H-2), 2.76
(1 H, d × d, J3A,2 5.5, J3A,3B 13.6, H-3A), 2.51 (partly obscured
by residual DMSO peak, ca. 1 H, d × d, J3B,2 9.25, J3B,3A 13.6,
H-3B) and 1.33 [18 H, overlapping singlets, C(CH3)3]; on add-
2
ition of H2O the multiplet at δ 4.01 simplified. A minor com-
ponent was evident in the 1H NMR spectrum (~18% by integra-
tion); the only distinct peak associated with this was an
exchangeable doublet at δ 6.77 (J 7.2); when the spectrum was
recorded at 332 K this peak was seen to have coalesced with the
major exchangeable doublet at δ 7.12; δC(125.76 MHz, C2HCl3)
170.76 and 164.28 (2 × CO), 155.28 (urethane), 154.07 (C-2Ј),
147.79 (C-4Ј), 124.90 (C-5Ј), 82.14 and 79.63 [2 × C(CH3)3],
53.39 (C-2), 30.97 (C-3), 28.25 and 27.98 [2 × C(CH3)3].
(2S)-2-Amino-3-(2-methyl-4-oxopyrimidin-5-yl)propionic acid
dihydrochloride 27b
Compound 26b (0.171 g, 0.48 mmol) was suspended in conc.
hydrochloric acid (1.5 ml) and stirred at room temperature for
1.5 h, during which time there was dissolution of the suspended
solid accompanied by slow effervescence. The solvent was
removed in vacuo with gentle warming, to yield the title com-
pound 27b as a hygroscopic glass (0.15 g, >100%); [α]2D3 ϩ54 (c
1, H2O); m/z (ϩve FAB, thioglycerol ϩ sodium) 242 ([M ϩ
2Na]ϩ), 220 ([M ϩ Na]ϩ) and 198 ([M ϩ H]ϩ) [Found: m/z (EI)
197.081 17 ([M]ϩ). C8H11N3O3 requires 197.080 04]; νmax(KBr)/
tert-Butyl (2S)-2-tert-butoxycarbonylamino-3-(2-phenyl-4-oxo-
pyrimidin 5-yl)propionate 26c
Compound 25 (1.113 g, 3.403 mmol), benzamidine hydro-
chloride monohydrate (2.13 g, 13.6 mmol) and potassium car-
bonate (0.94 g, 6.8 mmol) were heated in ethanol (30 ml) at
reflux for 44 h. The solvent was removed in vacuo and the
resultant oil was partitioned between ethyl acetate (20 ml) and
water (20 ml). The aqueous phase was separated and washed
with ethyl acetate (2 × 20 ml). The combined organic phases
were washed with brine, dried (MgSO4) and the solvent was
removed in vacuo to yield a yellow oil which solidified on
storage. This was recrystallised from ethanol to yield the title
compound 26c as a white solid (0.2 g, 14%). The mother liquors
were further purified, by chromatography on silica gel, eluting
with dichloromethane–methanol (95:5). Recrystallisation of
the product obtained from ethanol gave further white solid
(0.583 g, 41%; total yield 55%), mp 188–189 ЊC; [α]2D3 ϩ14.5 (c
1.3, CHCl3) (Found: C, 63.2; H, 7.3; N, 10.2. C22H29N3O5
requires C, 63.6; H, 7.0; N, 10.1%); m/z (ϩve FAB, 3-NBA) 831
([2M ϩ H]ϩ), 438 ([M ϩ Na]ϩ) and 416 ([M ϩ H]ϩ); νmax(KBr)/
cmϪ1 1725 (ester) and 1698 (urethane); λmax(MeOH, pH 7)/nm
246 and 299 (log ε 3.81 and 3.89); λmax(MeOH, pH 1)/nm 253
and 281 (log ε 3.88 and 3.94); δH (360 MHz, C2HCl3) 12.5 (1 H,
exch. br s, NH), 8.26 (2 H, m, ArH), 8.03 (1 H, s, H-4Ј), 7.52 (3
H, m, ArH), 5.96 (1 H, exch. d, JN H ,2 7.5, NH), 4.50 (1 H, m, H-
2), 3.02 (1 H, d × d, J3A,2 4.6 and J3A,3B 14, H-3A), 2.85 (1 H,
d × d, J3B,2 8.6 and 14, H-3B), 1.44 [9 H, s, C(CH3)3] and 1.33 [9
H, s, C(CH3)3]; δC(125.76 MHz, C2HCl3) 170.87 and 165.61
(2 × CO), 156.61 (C-2Ј), 155.34 (urethane), 131.91 (aromatic),
131.80 (ipso-C), 129.05 and 127.69 (aromatic), 121.83 (C-5Ј),
81.91 and 79.46 [C(CH3)3], 54.24 (C-2), 30.68 (C-3), 28.18 and
28.00 [2 × C(CH3)3].
cmϪ1 3541 (OH, NH) and 1662 (C᎐O); λmax(MeOH)/nm 227
᎐
and 275 (log ε 3.75 and 3.75); λmax(MeOH, pH 1)/nm 228 and
264 (log ε 3.84 and 3.68); λmax(MeOH, pH 12)/nm 235 and 275
2
(log ε 3.82 and 3.75); δH (360 MHz, H2O) 7.53 (1 H, s, H-4Ј),
3.72 (1 H, d × d, J2,3A 4.5, J2,3B 7.3, H-2), 2.76 (1 H, d × d, J3A,2
4.5, J3A,3B 14.9, H-3A), 2.59 (1 H, d × d, J3B,2 7.3, J3B,3A 14.9,
2
H-3B) and 2.11 (3 H, s, CH3); δC(125.76 MHz, H2O) 172.92
(CO H), 167.34 (C᎐O), 160.45 (C-2Ј), 149.51 (C-4Ј), 118.89 (C-
᎐
2
5Ј), 53.84 (C-2), 28.93 (C-3) and 20.09 (CH3).
(2S)-2-Amino-3-(2-phenyl-4-oxopyrimidin-5-yl)propionic acid
hydrochloride 27c
Compound 26c (0.117 g, 0.28 mmol) was dissolved in conc.
hydrochloric acid (1.5 ml). After 1 h at room temperature the
solvent was removed in vacuo with gentle warming to yield
the title compound 27c as a hygroscopic glass (0.15 g, >100%);
[α]2D3 ϩ0.5 (c 0.6, 2  HCl) [Found: m/z (EI) 259.086 40 ([M]ϩ).
C13H13N3O3 requires 259.095 69]; νmax(KBr)/cmϪ1 3012 (br,
OH, NH) and 1740 (C᎐O); λmax(MeOH, pH 7)/nm 243 and 287
᎐
(log ε 4.06 and 4.01); λmax(MeOH, pH 12)/nm 235 and 294 (log ε
2
4.20 and 3.91); δH (360 MHz, H2O) 7.90 (1 H, s, H-4Ј), 7.65 (2
H, m, ArH), 7.59 (1 H, m, ArH), 7.45 (2 H, m, ArH), 4.21 (1 H,
t, J ca. 6.3, H-2), 3.01 (1 H, d × d, J3A,2 6.3, J3A,3B 14.7, H-3A)
and 2.92 (1 H, d × d, J3B,2 7.0, J3B,3A 14.7, H-3B); δC(125.76
MHz, 2H O) 170.44 (CO H), 163.02 (C᎐O), 159.98 (C-2Ј),
᎐
2
2
tert-Butyl (2S)-2-tert-butoxycarbonylamino-3-(4-oxopyrimidin-
5-yl)propionate 26a
Compound 25 (0.94 g, 2.87 mmol), formamidine acetate (1.2 g,
142.94 (C-4Ј), 134.82 (aromatic), 129.55 and 128.33 (2 ×
aromatic), 125.59 (ipso-C), 121.23 (C-5Ј), 51.16 (C-2) and 28.03
(C-3).
1304
J. Chem. Soc., Perkin Trans. 1, 1997

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(2S)-2-Amino-3-(4-oxopyrimidin-5-yl)propionic acid hydro-
chloride 27a
mmol) was dissolved in tetrahydrofuran (20 ml) and cooled to
solid CO2–acetone bath temperature with stirring and under an
atmosphere of nitrogen. Lithium hexamethyldisilazide (1 
solution in THF; 13.2 ml, 13.2 mmol) was added dropwise to
the mixture and stirring was continued for 1 h; methyl formate
(1.48 ml, 24 mmol) was then added to the mixture. The solu-
tion was stirred for 5 min at the temperature of the solid CO2
bath, after which it was warmed to ice-bath temperature and
stirred for a further 100 min. The reaction was quenched by
addition of 5% aqueous citric acid (15 ml) to the mixture,
after which it was concentrated to a small volume in vacuo
and extracted with ethyl acetate (3 × 15 ml). The combined
organic phases were washed with 5% aqueous citric acid (10
ml) and brine, dried (MgSO4) and the solvent was removed in
vacuo to yield a tan coloured foam which was dissolved in
dioxane (20 ml). 2-Aminopyridine (5.31 g, 56 mmol) was
added to the solution which was then heated at reflux for 4 h.
After this the solvent was removed in vacuo and the resultant
oil was partitioned between ethyl acetate (30 ml) and water
(30 ml). The aqueous phase was separated and extracted with
ethyl acetate (2 × 20 ml). The combined organic phases were
washed with brine, dried (Na2SO4) and the solvent was
removed in vacuo to yield an oil which partially crystallised
when stored. A first crop of the title compound 31 was
obtained by precipitation from ethyl acetate (0.652 g). The
remaining solution was diluted with chloroform and washed
first with 5% aqueous citric acid (4 × 15 ml) until the wash-
ings remained acidic and then with brine. It was then dried
(MgSO4) and the solvent was removed in vacuo to yield a red
solid which was purified by recrystallisation from ethyl acet-
ate (2.972 g, 68% combined yield); mp 186–188 ЊC (decomp.);
[α]2D3 ϩ0.5 (c 0.7, CHCl3) (Found: C, 61.3; H, 6.9; N, 10.5.
C20H27N3O5 requires C, 61.7; H, 7.0; N, 10.8%); m/z (ϩve
FAB, thioglycerol) 412 ([M ϩ Na]ϩ) and 390 ([M ϩ H]ϩ);
νmax(KBr)/cmϪ1 1762 (imide) and 1637; λmax(MeOH, pH 7)/
nm 287 and 335 (log ε 4.19 and 4.40); λmax(MeOH, pH 1)/nm
280 and 342 (log ε 4.22 and 4.37); λmax(MeOH, pH 12)/nm
287 and 335 (log ε 4.17 and 4.48); δH (360 MHz, C2HCl3) 8.21
(1 H, m, ArH), 8.02 (1 H, d × t, J6,3 2.3, J6,N H 13.4, H-6),
7.62 (1 H, m, ArH), 6.91 (2 H, m, ArH), 6.84 (1 H, exch. d,
JN H ,6 13.4, NH), 4.56 (1 H, d × d, J2,3B 3.4, J2,3A 10.5, H-2),
2.98 (1 H, d × d × d, J3,6 2.3, J3A,2 10.5, J3A,3B 16.1, H-3A),
2.55 (1 H, d × d × d, J3,6 2.3, J3B,2 3.4, J3B,3A 16.1, H-3B), 1.52
[9 H, s, C(CH3)3] and 1.47 [9 H, s, C(CH3)3]; addition of
2H2O caused the d × t at δ 8.02 to collapse to a broadened
undefined triplet; δC(125.76 MHz, C2HCl3) 170.45 and 167.69
Compound 26a (0.743 g, 2.19 mmol) was dissolved in conc.
hydrochloric acid (3 ml). After 1.5 h at room temperature the
solvent was removed in vacuo to yield the title compound 27a
as a glassy hygroscopic solid (0.65 g, >100%), crystals of which
were obtained by slow precipitation from water–ethanol; mp
(slowly softens) >163 ЊC; [α]2D3 Ϫ15.8 (c 1, H2O) (Found: C, 30.8;
H, 4.6; N, 15.6. C7H9N3O3ؒ2HClؒH2O requires C, 30.7; H, 4.8;
N, 15.3%); m/z (ϩve FAB, glycerol) 393 ([2M ϩ Na]ϩ), 367
([2M ϩ H]ϩ) and 184 ([M ϩ H]ϩ); νmax(KBr)/cmϪ1 3100 (br,
NH, OH), 1737 (C᎐O) and 1709 (acid); λmax(MeOH, pH 7)/nm
᎐
226 and 272 (log ε 3.64 and 3.56); λmax(MeOH, pH 12)/nm 236
and 274 (log ε 3.28 and 3.58); λmax(MeOH, pH 1)/nm 228 and
2
267 (log ε 3.68 and 3.51); δH (360 MHz, H2O) 8.69 (1 H, s,
H-2Ј), 7.85 (1 H, s, H-4Ј), 4.15 (1 H, t, J 6.55, H-2), 2.99 (1 H,
d × d, J3A,2 6.5, J3A,3B 14.8, H-3A) and 2.88 (1 H, d × d, J3B,2 6.5,
J3B,3A 14.8, H-3B); δC(125.76 MHz, 2H2O) 171.18 (CO2H),
163.14 (CO), 151.26 (C-2Ј), 144.25 (C-4Ј), 124.19 (C-5Ј), 51.82
(C-2) and 28.93 (C-3).
tert-Butyl (2S)-2-tert-butoxycarbonylamino-3-(2-amino-4-oxo-
pyrimidin-5-yl)propionate 28
Compound 25 (1.2 g, 3.67 mmol) and guanidine carbonate
(1.98 g, 11 mmol) were heated in ethanol (20 ml) at reflux for
18 h. The solvent was removed in vacuo and the resultant oil
was partitioned between ethyl acetate (20 ml) and water (20 ml).
The aqueous phase was separated and washed with ethyl acet-
ate (2 × 20 ml). The combined organic phases were washed with
brine, dried (MgSO4) and the solvent was removed in vacuo to
yield a tan coloured oil. This was purified by chromatography
on silica gel, eluting with dichloromethane–methanol–acetic
acid (92:6:2) to yield the title compound 28 as a tan coloured
foam (0.504 g, 39%); [α]D23 Ϫ74 (c 2.4, CHCl3); m/z (ϩve FAB, 3-
NBA) 710 ([2M ϩ 2H]ϩ) and 355 ([M ϩ H]ϩ) [Found: m/z (EI)
253.130 13 ([M Ϫ Boc]ϩ). C11H17N4O3 requires 253.130 07];
νmax(film)/cmϪ1 1710 (ester) and 1670 (urethane); λmax(MeOH,
pH 7)/nm 229 and 290 (log ε 3.65 and 3.73); λmax(MeOH, pH 1)/
nm 229 and 263 (log ε 3.65 and 3.70); λmax(MeOH, pH 12)/nm
235 and 280 (log ε 3.68 and 3.72); δH (360 MHz, [2H6]-DMSO)
10.15 (1 H, br exch., NH), 7.35 (1 H, s, H-4Ј), 7.10 (1 H, exch. d,
J 7.6, NH), 6.45 (2 H, br exch., NH2), 4.00 (1 H, m, H-2), 2.59
(1 H, d × d, J3A,2 5.1, J3A,3B 13.7, H-3A), 2.38 (1 H, d × d, J3B,2
8.6, J3B,3A 13.7, H-3B) and 1.33–1.32 [18 H, overlapping sing-
lets, C(CH3)3]. A minor component was evident in the 1H NMR
spectrum, the only distinct peak being an exchangeable doublet
at δ 6.75; when the spectrum was recorded at 333 K this peak
coalesced with the major exchangeable doublet at δ 7.10.
(2 × CO), 152.60 (C᎐N), 150.05 (urethane), 148.50 (C-6Ј),
᎐
138.47 (C-6), 132.02, 117.74 and 108.16 (3 × aromatic),
102.53 (C-4), 82.72 and 82.06 [2 × C(CH3)3], 56.57 (C-2),
27.98, 27.88 [2 × C(CH3)3] and 24.43 (C-3).
(2S)-2-Amino-3-(2-amino-4-oxopyrimidin-5-yl)propionic acid
dihydrochloride 29
Compound 28 (0.50 g, 1.41 mmol) was dissolved in conc.
hydrochloric acid (5 ml) and the solution was left for 2 h at
room temperature. The solvent was then removed in vacuo
with gentle warming to yield the title compound 29 as an off-
white solid (0.45 g, >100%); mp 210 ЊC (decomp.); [α]2D3 Ϫ2.9 (c
1.8, H2O) [Found: m/z (EI) 198.076 74 ([M]ϩ). C7H10N4O3
requires 198.075 29]; νmax(film)/cmϪ1 3006 (br, NH, OH), 1740
tert-Butyl (2S)-2-tert-butoxycarbonylamino-3-(4-oxopyrido-
[1,2-a]pyrimidin-3-yl)propionate 32
Compound 31 (0.277 g, 0.71 mmol) and potassium carbonate
(0.2 g, 1.45 mmol) were heated in ethanol (10 ml) at reflux for
2 h after which the solvent was removed in vacuo. The resultant
mixture was partitioned between ethyl acetate (15 ml) and 10%
aqueous citric acid (10 ml). The aqueous phase was separated
and extracted with ethyl acetate (15 ml). The combined organic
phases were washed with brine, dried (MgSO4) and the solvent
was removed in vacuo to yield a yellow oil which was purified by
chromatography on silica gel, eluting with dichloromethane–
methanol (96.5:3.5). Residual starting material contaminated a
number of fractions but pure product was obtained as a yellow
solid (0.154 g, 55%). An analytical sample was further purified
by recrystallisation from diethyl ether–light petroleum ether (bp
60–80 ЊC) to yield the title compound 32 as a pale yellow solid,
mp 78–90 ЊC; [α]2D3 Ϫ39.2 (c 0.5, CHCl3); m/z (ϩve FAB,
3-NBA) 779 ([2M ϩ H]ϩ) and 390 ([M ϩ H]ϩ) [Found: m/z (EI)
389.195 01 ([M]ϩ). C20H27N3O5 requires 389.195 07]; νmax(KBr)/
(C᎐O) and 1690; λmax(MeOH, pH 7)/nm 220 and 263 (log ε 3.89
᎐
and 3.67); λmax(MeOH, pH 1)/nm 224 and 262 (log ε 3.60 and
3.66); λmax(MeOH, pH 12)/nm 220, 234 and 282 (log ε 3.66, 3.67
and 3.69); δH (360 MHz, 2H2O) 7.40 (1 H, s, H-4Ј), 4.05 (1 H, t, J
ca. 6.4, H-2), 2.83 (1 H, d × d, J3A,2 6, J3A,3B 15, H-3A) and 2.70
(1 H, d × d, J3B,2 7.0, J3B,3A 15.0, H-3B); δC(125.76 MHz, 2H2O)
170.25 (CO H), 161.99 (C᎐O), 151.42 (C-2Ј), 140.19 (C-4Ј),
᎐
2
110.75 (C-5Ј), 51.22 (C-2) and 26.96 (C-3).
tert-Butyl (2S)-1-tert-butoxycarbonyl-4-(2-pyridinyl)amino-
methylenepyroglutamate 31
tert-Butyl 1-tert-butoxycarbonylpyroglutamate25 (3.43 g, 12
J. Chem. Soc., Perkin Trans. 1, 1997
1305

View Article Online
cmϪ1 1713 (ester) and 1673 (urethane); λmax(MeOH, pH 7)/nm
242 and 339 (log ε 4.03 and 4.10); λmax(MeOH, pH 1)/nm 239
and 322 (log ε 3.92 and 4.03); λmax(MeOH, pH 12)/nm 242 and
339 (log ε 4.04 and 4.08); δH (360 MHz, C2HCl3) 9.07 (1 H, d, J
7.0, ArH), 8.21 (1 H, s, H-2Ј), 7.71 (1 H, t, J 7.2, ArH), 7.63 (1
H, d, J 8.9, ArH), 7.16 (1 H, t, J 6.75, ArH), 5.77 (1 H, exch. d,
JN H ,2 7.55, NH), 4.49 (1 H, m, H-2), 3.19 (1 H, d × d, J3A,2 4.6,
J3A,3B 13.8, H-3A), 2.98 (1 H, d × d, J3B,2 8.1, J3B,3A 13.8, H-3B),
1.43 [9 H, s, C(CH3)3] and 1.36 [9 H, s, C(CH3)3]; addition
J3B,3A 17.15, H-3B) and 1.40 [18 H, overlapping singlets,
2
C(CH3)3]; addition of H2O caused the peak at δ 7.58 to sim-
plify to a triplet with J 2.3; δC(125.76 MHz, [2H6]-DMSO)
170.86 and 167.14 (2 × CO), 156.58 (C᎐N), 149.38 (urethane),
᎐
132.52 (C-6), 105.30 (C-4), 82.01 and 81.68 [2 × C(CH3)3], 56.24
(C-2), 27.69 and 24.58 [2 × C(CH3)3].
Acknowledgements
2
We thank the EPSRC and the Wellcome Foundation for CASE
studentships (to A. N. B. and A. D.).
of H2O caused the multiplet at δ 4.49 to simplify to a d × d,
J2,3A 4.6, J2,3B 8; δC(125.76 MHz, C2HCl3) 170.89 (CO),
158.66 (C᎐N), 154.10 (C-2Ј), 150.66 (urethane), 135.49, 127.22,
᎐
126.34, 115.64 and 113.44 (5 × aromatic), 81.92 and 79.45
[2 × C(CH3)3], 54.14 (C-2), 31.39 (C-3), 28.21 and 27.97
[2 × C(CH3)3].
References
1 This work has been reported in preliminary form in (a) A. N.
Bowler, P. M. Doyle and D. W. Young, J. Chem. Soc., Chem.
Commun., 1991, 314; and (b) A. Dinsmore, P. M. Doyle and
D. W. Young, Tetrahedron Lett., 1995, 36, 7503.
2 D. R. Curtis, J. W. Phillis and J. C. Watkins, Nature ( London) , 1959,
183, 611.
(2S)-2-Amino-3-(4-oxopyrido[1,2-a]pyrimidin-3-yl)propionic
acid hydrochloride 33
Compound 32 (30 mg, 0.08 mmol) was dissolved in conc.
hydrochloric acid (ca. 1 ml) at room temperature. When effer-
vescence had ceased (ca. 30 s) the solvent was removed in
vacuo to yield the title compound 33 as a glassy solid (28 mg,
>100%); [α]2D3 Ϫ3.9 (c 1, H2O) [Found: m/z (EI) 233.079 49
([M]ϩ). C11H11N3O3 requires 233.080 04]; λmax(MeOH, pH 7)/
nm 242 and 348 (log ε 3.78 and 3.83); λmax(MeOH, pH 1)/nm
239 and 320 (log ε 3.64 and 3.79); λmax(MeOH, pH 12)/nm 243
and 339 (log ε 3.82 and 3.84); δH (360 MHz, 2H2O) 9.03 (1 H, d,
J 6.9, ArH), 8.27 (1 H, d × d, J 7.4 and 8.6, ArH), 8.17 (1 H, s,
H-2Ј), 7.80 (1 H, d × d, J 1.2 and 8.6, ArH), 7.61 (1 H, t, J 7.1,
ArH), 4.21 (1 H, t, J ca. 6.5, H-2), 3.17 (1 H, d × d, J3A,2 6.5,
J3A,3B 14.9, H-3A) and 3.05 (1 H, d × d, J3B,2 6.6, J3B,3A 14.9,
H-3B); irradiation of the doublet at δ 9.03 showed a change in
the appearance of the triplet at δ 7.61; irradiation at the d × d at
δ 8.27 showed a change in appearance of the d × d at δ 7.80 and
3 R. J. Bridges, J. W. Geddes, D. T. Monaghan and C. W. Cotman, in
Excitatory Amino Acids in Health and Disease, ed. D. Lodge, Wiley,
New York, 1988, p. 321.
4 S. Patel, A. G. Chapman, M. H. Millan and B. S. Meldrum, in
Excitatory Amino Acids in Health and Disease, ed. D. Lodge, Wiley,
New York, 1988, p. 353.
5 G. K. Steinberg, J. Saleh, D. Kunis, R. DeLaPaz and S. R. Zarnegar,
Stroke, 1989, 20, 1247.
6 J. J. Hansen and P. Krogsgaard-Larsen, J. Chem. Soc., Perkin Trans.
1, 1980, 1826.
7 P. Krogsgaard-Larsen, L. Brehm, J. S. Johansen, P. Vinzents,
J. Lauridsen and D. R. Curtis, J. Med. Chem., 1985, 28, 673.
8 T. Honoré and J. Lauridsen, Acta Chem. Scand., Sect. B, 1980, 34,
235.
9 J. Lauridsen, T. Honoré and P. Krogsgaard-Larsen, J. Med. Chem.,
1985, 28, 668.
10 U. Madsen and E. H. F. Wong, J. Med. Chem., 1992, 35, 107.
11 I. T. Christensen, B. Ebert, U. Madsen, B. Nielsen, L. Brehm and
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12 M. Begtrup and F. A. Sløk, Synthesis, 1993, 861.
13 J. J. Hansen, J. Lauridsen, E. Nielsen and P. Krogsgaard-Larsen,
J. Med. Chem., 1983, 26, 901.
2
the triplet at δ 7.61; δC(125.76 MHz, H2O) 171.57 and 157.74
(2 × CO), 147.21 (NC᎐N), 145.45, 143.21, 129.65, 121.13,
᎐
118.84 and 111.25 (aromatic), 52.41 (C-2) and 29.36 (C-3).
14 J. J. Hansen, B. Nielsen, P. Krogsgaard-Larsen, L. Brehm,
E. Ø. Nielsen and D. R. Curtis, J. Med. Chem., 1989, 32, 2254.
15 B. Ebert, S. Lenz, L. Brehm, P. Bregnedal, J. J. Hansen,
K. Frederiksen, K. P. Bøgesø and P. Krogsgaard-Larsen, J. Med.
Chem., 1994, 37, 878.
16 J. J. Hansen, F. S. Jørgensen, T. M. Lund, B. Nielsen, A. Reinhardt,
I. Breum, L. Brehm and P. Krogsgaard-Larsen, in Excitatory
Amino Acid Receptors—Design of Agonists and Antagonists, ed.
P. Krogsgaard-Larsen and J. J. Hansen, Ellis Horwood, New York,
1992, p. 216.
17 H. Gibian and H. Klieger, Liebigs Ann. Chem., 1961, 640, 145.
18 S. Danishefsky, E. Berman, L. A. Clizbe and M. Hirama, J. Am.
Chem. Soc., 1979, 101, 4385.
19 X. Durand, P. Hudhomme, J. A. Khan and D. W. Young, J. Chem.
Soc., Perkin Trans. 1, 1996, 1131.
20 R. A. August, D. Phil Thesis, Sussex, 1987.
21 S. Tsubotani, Y. Funabashi, M. Takamoto, S. Hakoda and
S. Harada, Tetrahedron, 1991, 47, 8079.
22 These experiments were conducted by Dr G. Ormandy, The
Wellcome Research Laboratories, Beckenham.
23 R. H. Evans, A. W. Jones and J. C. Watkins, J. Physiol., 1980, 308,
71P.
tert-Butyl (2S)-1-tert-butoxycarbonyl-4-tetrazol-5-ylamino-
methylenepyroglutamate 34
Compound 23 (0.65 g, 1.91 mmol) and screened Methyl Orange
(1 drop) were dissolved in methanol (10 ml) with stirring at
room temperature. 1  Aqueous hydrochloric acid (ca. 3.2 ml
required) was added dropwise to the mixture at such a rate as to
keep the pH of the solution at or above the neutral point of the
indicator and until the indicator remained red. The solution
was concentrated to a small volume in vacuo, diluted with water
(10 ml) and extracted with ethyl acetate (3 × 15 ml). The com-
bined organic layers were washed with brine, dried (MgSO4)
and the solvent was removed in vacuo to yield a yellow oil which
was dissolved in a mixture of ethanol (8 ml) and water (2 ml)
with aminotetrazole monohydrate (0.395 g, 3.8 mmol) and
heated at reflux for 1 h 40 min. Potassium carbonate (0.53 g, 3.8
mmol) was added to the mixture and heating at reflux was
resumed for a further 4 h. The solvent was removed in vacuo
and the resultant oily solid was partitioned between ethyl acet-
ate (30 ml) and water (30 ml). The aqueous phase was separated
and acidified by addition of acetic acid (5 ml) causing an
instant precipitate which was filtered off, washed with water
and dried in vacuo to yield the title compound 34 as a white
solid (0.512 g, 70%). A sample was recrystallised from ethanol;
mp 183 ЊC (decomp.); m/z (ϩve FAB, 3-NBA) 783 ([2M ϩ
Na]ϩ), 403 ([M ϩ Na]ϩ) and 381 ([M ϩ H]ϩ); νmax(KBr)/cmϪ1
1773 (imide) and 1694 (urethane); λmax(MeOH, pH 7)/nm 221
and 297 (log ε 3.76 and 4.48); no change on addition of acid;
λmax(MeOH, pH 12)/nm 310 (log ε 4.57); δH (360 MHz, [2H6]-
DMSO) 15.9 (1 H, br exch., NH), 10.48 (1 H, exch. d, JN H ,6
12.1, NH), 7.58 (1 H, d × t, J6,3 ca. 2.3, J6,N H 12.1, H-6), 4.53 (1
H, d × d, J2,3B 2.8, J2,3A 10.7, H-2), 2.99 (1 H, d × d × d, J3A,6
2.4, J3A,2 10.8, J3A.3B 17.15, H-3A), 2.60 (1 H, d × t, J3B,2;3B,6 2.8,
24 H. Sugiyama, M. Watanabe, H. Taji, Y. Yamamoto and I. Ito,
Neurosci. Res., 1989, 7, 164.
25 R. A. August, J. A. Khan, C. M. Moody and D. W. Young, J. Chem.
Soc., Perkin Trans. 1, 1996, 507.
26 R. R. Williams, A. E. Ruehle and J. Finkelstein, J. Am. Chem.
Soc., 1937, 59, 526.
27 A. Batchelor, A. Dinsmore, P. M. Doyle and D. W. Young,
unpublished observations.
28 The test measures the ability of a compound to block the action of
trans-aminocyclopentanedicarboxylic acid (ACPD) in Purkinje type
rat neurones.
Paper 6/08067G
Received 28th November 1996
Accepted 27th January 1997
1306
J. Chem. Soc., Perkin Trans. 1, 1997