A simple method for the preparation of 3-hydroxyiminodehydroquinate, a potent inhibitor of type II dehydroquinase

Article abstract of DOI:10.1039/b206066c

A number of routes to 3-hydroxyiminodehydroquinate 4, one of the most potent inhibitors of type II dehydroquinase that is currently known, have been investigated. Methods based on the existing literature synthesis, i.e. oxime formation of a suitably C-4 a

Full text of DOI:10.1039/b206066c

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A simple method for the preparation of 3-hydroxyiminodehydro-
quinate,† a potent inhibitor of type II dehydroquinase
Christine Le Sann,*a Chris Abellb and Andrew D. Abell*a
1
a Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch,
New Zealand. E-mail: chem237@its.canterbury.ac.nz; Fax: ϩ(64) (0)3 364 2110
b University Chemical Laboratory, Lensfield Road, Cambridge, UK CB2 1EW.
E-mail: ca26@cam.ac.uk; Fax: ϩ(44) (0)1223 336 362
Received (in Cambridge, UK) 24th June 2002, Accepted 24th July 2002
First published as an Advance Article on the web 16th August 2002
A number of routes to 3-hydroxyiminodehydroquinate 4, one of the most potent inhibitors of type II dehydroquinase
that is currently known, have been investigated. Methods based on the existing literature synthesis, i.e. oxime
formation of a suitably C-4 and C-5 protected methyl 3-dehydroquinate derivative were initially studied. Benzoyl
protection as in 11 did give the desired product but in low overall yield. An alternative BBA protection strategy
starting with 7 was successful in generating a C-4/C-5 analogue of the desired oxime 4 in high yield. Further
investigation revealed that it was unnecessary to protect the dehydroquinate precursor, hence the potassium
salt corresponding to oxime 4 was simply synthesised as a single isomer from methyl dehydroquinate 10.
ality into the binding pocket of the type II enzyme that
Introduction
normally6 stabilises the developing negative charge of a bio-
Types I and II dehydroquinase catalyse the dehydration of 3-
dehydroquinate 1 to 3-dehydroshikimate 3. The type II enzyme
synthetic enolate intermediate 2.5 By contrast, the type I
enzyme operates via a mechanism involving the formation of
operates in the catabolic quinate pathway, thus allowing fungi
a series of imine–enamine intermediates7,8 rather than via
to use quinic acid as a carbon source (Scheme 1).1 By contrast,
an enolate intermediate. The stabilising effect of the oxime
inhibitor is therefore not possible in this case. This potential
mechanistic basis for the selectivity and potency of 4 towards
the dehydroquinases provides a basis for further inhibitor
design. Accordingly, a convenient and reliable method for the
synthesis of this deceptively simple molecule, and its analogues,
is required.
Oxime 4 has previously been prepared as the sodium salt
from quinic acid, in eight steps and 6–9% overall yield.5 This
preparation requires a lengthy and tedious series of protections
Scheme 1
and deprotections of quinic acid to allow selective function-
alisation at C-3.9 It also gives rise to mixtures of isomers at two
both types I and II enzymes are utilised in the shikimate
pathway—the biosynthetic pathway by which aromatic amino
acids and essential aromatic compounds such as folate and
key steps which contributes to the low overall yield. Herein we
describe an efficient and simple method for the synthesis of this
oxime from 3-dehydroquinic acid 6 (Scheme 3). This synthetic
ubiquinone are produced in nature.2 The shikimate pathway
is only present in plants, fungi and bacteria, but not in
mammals. A very exciting and recent development is the
recognition that the shikimate pathway plays an important
role in the apicomplexin parasites such as Toxoplasma gondii,
Plasmodium falciparum (malaria), and Cryptosporidium parvum,
and that inhibition of the pathway can retard parasitic
growth.3
route was made possible by our recently published10 synthesis
of 6 from quinic acid 5 (see Scheme 2, 53% overall yield).
Analogues with C-4 and C-5 protection have also been
prepared (Scheme 3).
Results and discussion
A number of alternative approaches to 4 were investigated
(see Scheme 3). Initially, we attempted to simplify the published
route by using methyl 3-dehydroquinate bearing a protecting
group for the hydroxy groups at C-4 and C-5 as the starting
material for the introduction of the oxime functionality at C-3.
The butane 2,3-bisacetal (BBA) protected11 dehydroquinate 7,
available in our laboratory as a precursor to dehydroquinic acid
6,10 was simply treated with hydroxylamine hydrochloride in the
presence of sodium acetate to afford the oxime 8 in 92% yield
and as a single isomer (Scheme 3). The methyl ester of 8 was
carefully hydrolysed using sodium hydroxide at room temper-
ature to afford the oxime as the sodium salt 9 which gave
satisfactory characterisation data. While this sequence provided
access to a useful dehydroquinate-based oxime, it did not allow
These facts, together with the recent determination of crystal
structures of the dehydroquinases4 highlight the need to develop
inhibitors of these enzymes as new and novel antibiotic and
herbicide leads. One such compound, oxime 4, has recently
been shown to be selective for type II dehydroquinases over
type I and to exhibit selectivity amongst the type II enzymes,
being more potent against the enzymes from the bacterium M.
tuberculosis and the fungi A. nidulans, than the enzyme from the
bacterium S. coelicolor.5 It has been suggested that the type
selectivity of 4 is a result of positioning of the oxime function-
† The IUPAC name for 3-hydroxyiminodehydroquinate is (1S,4R,5R)-
1,4,5-trihydroxy-3-(hydroxyimino)cyclohexane-1-carboxylate.
DOI: 10.1039/b206066c
J. Chem. Soc., Perkin Trans. 1, 2002, 2065–2068
This journal is © The Royal Society of Chemistry 2002
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chloride following conditions developed by Mercier et al. for
the esterification of methyl quinate.12 The desired dibenzoyl
ester 11 was isolated in a low 8% yield after column chroma-
tography and crystallisation.§ A further two fractions were
obtained that contained complex mixtures of benzoylated
dehydroquinates and dehydroshikimates. Despite the low yield
of 11, a sufficient quantity was obtained to investigate oxime
formation. Dehydroquinate 11 was reacted with hydroxylamine
hydrochloride and sodium hydroxide to give the oxime 12 which
was not purified. This sample was then saponified with sodium
hydroxide to give the desired oxime salt 4 in a mixture with
sodium benzoate and sodium acetate. Further purification was
not attempted since parallel studies using the unprotected
dehydroquinates proved more successful.
In the next method, hydrolysis of 10 gave potassium dehydro-
quinate 1310 which was then reacted directly with hydroxyl-
amine hydrochloride. It was thought that the carboxylate
functionality of 13 would act as an internal base to liberate free
hydroxylamine from its hydrochloride salt and hence minimise
the likelihood of forming dehydroshikimate derivatives via
dehydration at C-1. To this end, 13 was treated with one equiv-
alent of hydroxylamine hydrochloride. The reaction afforded
an inseparable mixture of the oxime 14 and dehydroquinic acid
6 (9 : 1 by 1H-NMR). Although it is possible that this reaction
could be completed with more careful control of pH, it was
thought more expedient to simply perform the saponification
after the conversion to the oxime. Hence, in the final and
successful method, methyl dehydroquinate 10 was treated with
hydroxylamine hydrochloride (1 equiv.) and sodium acetate
(1 equiv.). In this case the oxime 15 was obtained as a single
isomer (97%) that was fully characterised. The methyl ester of
15 was then carefully hydrolysed using potassium hydroxide
to give the desired potassium 3-hydroxyiminodehydroquinate
16 (97%) which gave essentially equivalent data to 4.5
Conclusion
The hydroxyiminodehydroquinate 16 has been synthesised in
five steps from quinic acid 5 in 50% yield. A C-4/C-5 analogue
9 has also been prepared in excellent overall yield. The method
presented provides a simple and inexpensive route to this
important class of dehydroquinase inhibitor.
Scheme 2
Experimental
General
1H-NMR spectra were obtained using a Varian Unity 300
NMR spectrometer or a Varian Inova 500 spectrometer at
300 and 500 MHz respectively. 13C-NMR spectra were recorded
at a frequency of 75 MHz on a Varian Unity 300 spectrometer.
1H–13C-NMR Correlation experiments were carried out on a
Varian Inova 500 spectrometer. Chemical shifts (δ) are given
in parts per million (ppm). Mass spectra were recorded on a
Kratos MS80RFA instrument for electron impact (EI) tech-
nique, or a Micromass LCT spectrometer for the time-of-flight
(TOF) method. Infrared spectra were obtained on a Shimadzu
Hyper FT-IR instrument. Optical rotations were measured
using a Perkin 341 spectrometer. Melting points were taken on
an Electrothermal® apparatus and are uncorrected.
Scheme 3 i. H2NOHؒHCl, NaOAc, 92%; ii. NaOH, H2O, 98%; iii.
BzCl, pyridine, 8%; iv. H2NOHؒHCl, NaOAc; v. NaOH, H2O; vi.
H2NOHؒHCl; vii. H2NOHؒHCl, NaOAc, 96%, viii. KOH, H2O, 97%.
preparation of the desired oxime 4 since the conditions for
removing the protecting group are not compatible with the
oxime functionality.‡
Next we investigated three routes to the oxime 4 starting
from methyl 3-dehydroquinate 10, itself derived from 7 by
deprotection of the BBA group10 (see A, B and C, Scheme 3).
The first of these methods involved protecting the C-4 and C-5
hydroxy groups of 10 with a base-labile protecting group. This
alternative to the BBA protection (see 7 above) allows concom-
itant removal of all protecting groups under conditions that are
compatible with the oxime functionality. Consequently, methyl
dehydroquinate 10 was treated with pyridine and benzoyl
Methyl (1S,3E,4R,5R)-4,5-[(2S,3S )-2,3-dimethoxybutane-2,3-
diyldioxy)]-1-hydroxy-3-(hydroxyimino)cyclohexane-1-
carboxylate 8
To a solution of protected dehydroquinic acid 710 (100 mg,
0.31 mmol) in methanol (1 mL) were added hydroxylamine
‡ Oxime 9 might prove useful for determining the importance of the
hydroxy groups at C-4 and C-5 to inhibitory activity.
§ Delfourne et al. (see ref. 13) have reported a low 10% yield for the
acetylation of methyl dehydroquinate.
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hydrochloride (26 mg, 0.37 mmol) and sodium acetate (60 mg,
0.4 mmol) and the mixture was left to stir at room temperature
for 15 hours. Methanol was removed under reduced pressure,
and the residue was partitioned between ethyl acetate (15 mL)
and water (15 mL). The organic layer was separated, and the
aqueous layer was extracted with ethyl acetate (3 × 30 mL). The
combined organic layer was dried over magnesium sulfate, then
concentrated in vacuo to afford the oxime 8 as a glass (95 mg,
92%). Mp 117–120 ЊC; [α]2D0 ϩ88.5 (c 0.47 in CHCl3) (Found C,
49.06, H, 7.08, N, 3.90, C14H23O8Nؒ½H2O requires C, 49.10, H,
7.08, N, 4.08%); νmax(KBr)/cmϪ1 3340, 2954, 1738, 1450, 1379;
δH (CDCl3, 300 MHz) 1.16 (3H, s, 2Ј-CH3 or 3Ј-CH3), 1.19 (3H,
s, 2Ј-CH3 or 3Ј-CH3), 1.96 (2H, m, 6-H2), 2.11 (1H, d, J 15,
2-HH), 3.16 (3H, s, OCH3), 3.41 (3H, s, OCH3), 3.45 (1H, dd,
J 15, 2, 2-HH), 3.72 (3H, s, CO2CH3), 4.02 (1H, ddd, J 10, 10,
5.5, 5-H), 4.18 (1H, d, J 10, 4-H); δC (CDCl3, 75 MHz) 17.1
(2Ј-CH3 or 3Ј-CH3), 17.3 (2Ј-CH3 or 3Ј-CH3), 32.8 (C-2), 36.8
(C-6), 47.4 (2Ј-OCH3 or 3Ј-OCH3), 47.7 (2Ј-OCH3 or 3Ј-OCH3),
52.8 (CO2CH3), 67.0 (C-5), 71.3 (C-4), 73.6 (C-1), 99.2 (C-2Ј or
C-3Ј), 99.7 (C-2Ј or C-3Ј), 149.5 (C-3), 174.3 (CO2CH3); m/z
(EI) 302 (Mϩ Ϫ OCH3, 7%), 242 (18), 167 (93), 151 (41), 101
(100), 75 (50).
ar H × 4); δC (CDCl3, 75 MHz) 38.3 (C-6), 48.6 (C-2), 53.7
(OCH3), 70.6 (C-5), 73.4 (C-1), 78.9 (C-4), 128.4–133.4 (ar
C × 12), 165.3 (4-CO2Ph or 5-CO2Ph), 165.7 (4-CO2Ph or
5-CO2Ph), 196.6 (C-3).
Sodium (1S,3E,4R,5R)-1,4,5-trihydroxy-3-(hydroxyimino)-
cyclohexane-1-carboxylate 4
To a solution of triester 11 (120 mg, 0.30 mmol) in water and
methanol (1 : 2, 4 mL) were added sodium acetate trihydrate
(180 mg, 1.32 mmol) and hydroxylamine hydrochloride (85 mg,
1.22 mmol). The mixture was left to stir overnight at room
temperature. The methanol was evaporated under reduced
pressure, and the aqueous layer was extracted with ethyl acetate
(3 × 15 mL). The combined organic phases were dried over
magnesium sulfate, then evaporated in vacuo to give the oxime
12 (124 mg) which was not purified further. δH (CDCl3, 300
MHz) 2.35 (1H, dd, J 13, 11, 6-HH), 2.52 (1H, d, J 15, 2-HH),
2.51–2.58 (1H, m, 6-HH), 3.63 (1H, dd, J 15, 3, 2-HH), 3.82
(3H, s, CO2CH3), 5.80 (1H, dt, J 10.5, 9.5, 5-H), 5.93 (1H, d,
J 9.5, 4-H); δC (CDCl3, 75 MHz) 33.0 (C-2), 38.1 (C-6), 53.4
(CO2CH3), 71.1 (C-5), 72.9 (C-4), 73.3 (C-1), 128.1-133.3 (ar C
× 12), 149.9 (C-3), 165.4 (4-CO2Ph or 5-CO2Ph), 165.7
(4-CO2Ph or 5-CO2Ph), 174.1 (CO2CH3); m/z (TOF) found
428.1345 (C22H21O8N requires 428.1345), 428 (MHϩ, 100%),
413 (25).
Sodium (1S,3E,4R,5R)-4,5-[(2S,3S )-2,3-dimethoxybutane-2,3-
diyldioxy)]-1-hydroxy-3-(hydroxyimino)cyclohexane-1-
carboxylate 9
A solution of oxime 12 (100 mg, 0.23 mmol) in diethyl ether
(2 mL) was treated with an aqueous solution of sodium hydrox-
ide (2.5 M, 0.3 mL, 0.75 mmol) and stirred vigorously for 5 min.
The reaction mixture was evaporated to dryness in vacuo to give
the desired oxime 4 in a mixture with sodium benzoate and
sodium acetate as an off-white solid (110 mg, 4.5 : 4.5 : 1 by
1H-NMR). Selected data for oxime 4:5 δH (D2O, 300 MHz)
1.90 (2H, m, 6-H2), 2.12 (1H, d, J 15, 2-HH), 3.12 (1H, J 15, 2,
2-HH), 3.66 (1H, ddd, J 10, 9, 5.5, 5-H), 3.97 (1H, d, J 9,
4-H).
A solution of oxime 8 (300 mg, 0.90 mmol) in diethyl ether
(20 mL) was treated with an aqueous solution of sodium
hydroxide (2.5 M, 0.65 mL). The reaction mixture was stirred
vigorously at room temperature for 5 min. The water was
evaporated in vacuo to afford the crude product that was
recrystallised from ethanol to give oxime 9 as white plates
(302 mg, 98%). Mp 122–124 ЊC; [α]2D0 ϩ51.4 (c 1.03 in H2O)
(Found C, 39.50, N, 3.25, C13H23O8NNaؒ3H2O requires C,
39.50, N, 3.54%); νmax(KBr)/cmϪ1 3327, 2949, 1596, 1386, 1130,
1031; δH (D2O, 300 MHz) 1.22 (3H, s, 2Ј-CH3 or 3Ј-CH3), 1.27
(3H, s, 2Ј-CH3 or 3Ј-CH3), 1.80 (1H, m, 6-HH), 1.90 (1H, dd,
J 13, 11.5, 6-HH), 2.19 (1H, d, J 15, 2-HH), 3.15 (3H, s,
2Ј-OCH3 or 3Ј-OCH3), 3.18 (3H, s, 2Ј-OCH3 or 3Ј-OCH3), 3.24
(1H, dd, J 15, 2.5, 2-HH), 3.59 (1H, m, 5-H), 4.28 (1H, d,
J 10.5, 4-H); δC (D2O, 75 MHz) 17.1 (2Ј-CH3 or 3Ј-CH3),
17.3 (2Ј-CH3 or 3Ј-CH3), 32.8 (C-2), 36.8 (C-6), 47.4 (2Ј-OCH3
or 3Ј-OCH3), 47.7 (2Ј-OCH3 or 3Ј-OCH3), 52.8 (CO2CH3), 67.0
(C-5), 71.3 (C-4), 73.6 (C-1), 99.2 (C-2Ј or C-3Ј), 99.7 (C-2Ј
or C-3Ј), 149.5 (C-3), 174.3 (CO2CH3); m/z (TOF) found
318.1197, C13H20O8N requires 318.1189; 318 (M Ϫ Naϩ, 100%),
305 (34).
(1S,3E,4R)-1,4,5-Trihydroxy-3-(hydroxyimino)cyclohexane-1-
carboxylic acid 14
To a solution of potassium dehydroquinate 1310 (122 mg, 0.53
mmol) in water (1 mL) was added hydroxylamine hydrochloride
(37 mg, 0.53 mmol) and the mixture was left to stir for 3 h at
room temperature. The solvent was removed in vacuo to afford
an inseparable mixture of the oxime 14 and dehydroquinic acid
6 and potassium chloride as a white hygroscopic solid (155 mg,
9 : 1 by 1H-NMR). Selected data for oxime 14: νmax(KBr)/cmϪ1
3400, 1716, 1651, 1226; δH (D2O, 300 MHz) 1.93 (1H, dd,
J 13.0, 11.5, 6-HH), 2.07 (1H, br m, 6-HH), 2.24 (1H, d, J 14.5,
2-HH), 3.30 (1H, dd, J 14.5, 1.5, 2-HH), 3.69 (1H, br m, 5-H),
4.04 (1H, d, J 9.5, 4-H); δC (D2O, 75 MHz) 31.9 (C-2), 39.4
(C-6), 71.1 (C-5), 74.0 (C-1), 74.6 (C-4), 156.4 (C-3), 177.4
(CO2H). Dehydroquinic acid 6:10 δH (D2O, 300 MHz) 2.20 (1H,
m, 6-H2), 2.46 (1H, br d, J 14, 2-HH), 3.02 (1H, d, J 14, 2-HH),
3.79 (1H, m, 5-H), 4.18 (1H, d, J 9.5, 4-H); δC (D2O, 75 MHz)
39.4 (C-6), 47.6 (C-2), 71.4 (C-5), 74.0 (C-1), 80.6 (C-4), 177.4
(CO2H), (C-3 not observed).
Methyl (1R,4S,5R)-4,5-bis(benzoyloxy)-1-hydroxy-3-oxocyclo-
hexane-1-carboxylate 11
A solution of methyl dehydroquinate 1010 (122 mg, 0.60 mmol)
in acetone (1 mL) was cooled to Ϫ10 ЊC and then treated with
triethylamine (2 mL). After 5 min, benzoyl chloride (0.28 mL,
330 mg, 2.4 mmol) was added dropwise and the mixture was left
to stir for 2 h at which time the reaction was quenched by
addition of aqueous hydrochloric acid (0.1 M, 15 mL). The
resulting crude mixture was extracted with ethyl acetate (3 ×
30 mL). The combined organic phases were washed with brine
(50 mL), dried over magnesium sulfate, and concentrated under
reduced pressure. The crude mixture was purified by column
chromatography using 40% ethyl acetate in petroleum ether to
give the dibenzoylated compound 11 as a colourless solid which
was recrystallised from diethyl ether (20 mg, 8%). Mp 58–60 ЊC;
[α]2D0 Ϫ94.8 (c 1.8 in CH2Cl2) (Found C,64.07, H, 4.89,
C22H20O8.H2O requires C, 64.07, H, 4.89%); νmax(KBr)/cmϪ1
3479, 1728, 1600, 1452, 1282, 1253, 1070; δH (CDCl3, 300 MHz)
2.55 (1H, m, 6-HH), 2.68–2.81 (2H, m, 6-HH and 2-HH), 3.13
(1H, d, J 14, 2-HH), 3.85 (3H, s, CO2CH3), 5.86–5.97 (2H, m,
4-H and 5-H), 7.35–7.58 (6H, m, ar H × 6), 7.95–8.22 (4H, m,
Methyl (1S,3E,4R,5R)-3-(hydroxyimino)-1,4,5-trihydroxycyclo-
hexane-1-carboxylate 15
A solution of methyl dehydroquinate 1010 (230 mg, 1.13 mmol)
in water (2 mL) was added to sodium acetate trihydrate (153
mg, 1.13 mmol) and hydroxylamine hydrochloride (83 mg, 1.13
mmol). The mixture was left stirring at room temperature for
1.5 h, before it was concentrated under reduced pressure.
Methanol (3 mL) was added to the residue, and the insoluble
residue of sodium chloride was filtered off over Celite. The
filtrate was evaporated under reduced pressure to give a thick
oil which was dried under high vacuum to afford the oxime 15
as a very hygroscopic white solid (250 mg, 96%). Mp 99–100 ЊC;
J. Chem. Soc., Perkin Trans. 1, 2002, 2065–2068
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[α]2D0 Ϫ25.5 (c 1.06 in MeOH) (Found C, 43.08, H, 6.01, N, 6.02,
C8H13O6Nؒ¼H2O requires C, 42.94, H, 6.08, N, 6.25%);
νmax(KBr)/cmϪ1 3415, 2856, 2341, 1732, 1633, 1373, 1087;
δH (acetone-d6, 500 MHz) 1.88 (1H, m, 6-HH), 2.10 (1H, ddd,
J 13.5, 5, 2.5, 6-HH), 2.24 (1H, d, J 15, 2-HH), 3.32 (1H, dd,
J 15, 2.5, 2-HH), 3.70 (3H, s, CO2CH3), 3.76 (1H, ddd, J 11, 9,
5, 5-H), 4.08 (1H, d, J 9, 4-H); δC (D2O, 75 MHz) 32.1 (C-2),
40.1 (C-6), 52.1 (CO2CH3), 71.9 (C-5), 74.1 (C-4), 78.5 (C-1),
154.0 (C-3), 174.8 (CO2CH3); m/z (TOF) found 220.0821,
C8H14NO requires 220.0821; 220 (MHϩ, 100).
Acknowledgements
We are pleased to acknowledge financial support from a Royal
Society of New Zealand Marsden Grant.
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