A novel building block for the synthesis of isofagomin analogues

Article abstract of DOI:10.1016/S0957-4166(98)00090-1

The de novo synthesis of the novel potent building blocks phenyl (R)-3- acetoxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate (-)-7 and pheny (S)-3- butyryl-oxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate (+)-8 starting from commercially available methyl-1-

Full text of DOI:10.1016/S0957-4166(98)00090-1

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 9 (1998) 1519–1524
A novel building block for the synthesis of isofagomin analogues
Hans-Josef Altenbach ∗ and Gaetano Blanda †
Bergische Universität — GH Wuppertal, Fachbereich Chemie, Gaußstr. 20, D-42119 Wuppertal, Germany
Received 17 February 1998; accepted 2 March 1998
Abstract
The de novo synthesis of the novel potent building blocks phenyl (R)-3-acetoxymethyl-3,6-dihydro-2H-pyridine-
1-carboxylate (−)-7 and phenyl (S)-3-butyryl-oxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate (+)-8 starting
from commercially available methyl-1-benzyl-4-oxo-3-piperidinecarboxylate is described. The key steps are the
enantioselective esterification of the racemic alcohol 6 and the enantioselective hydrolysis of the racemic acetate
5, respectively, using lipase P from Pseudomonas caepacia. © 1998 Elsevier Science Ltd. All rights reserved.
1. Introduction
Sugar analogues, in which the ring oxygen of a pyranose has been replaced by nitrogen1 — commonly
known as azasugars — have often been found to be specific and effective inhibitors of enzymes which are
involved in the building up or cleavage of glycosides of the related sugar,2 thereby having the potential
to produce beneficial therapeutic effects such as cancerostatic3 or antiviral activities.4 Recently it has
been shown that piperidine systems where the nitrogen is at the position of the anomeric carbon of
the corresponding sugar are also very potent glycosidase inhibitors.5 All of the known routes to these
compounds (isofagomin and some derivatives) start from the chiral pool6 and are not very flexible.
A potent building block is 3-hydroxymethyl-1,2,3,6-tetrahydropyridine 1 or a protected form of the
alcohol, which has potential not only for the synthesis of isofagomin, but also for the synthesis of
stereoisomeric isofagomin analogues (Scheme 1).
We want to present an easy synthesis of the enantiomerically pure building block 1 by using enzymatic
resolution. To our knowledge neither such an approach for the synthesis of isofagomin analogues nor the
preparation of the enantiomerically pure alcohol 1 has been reported in the literature, only the synthesis
of a racemic derivative of 1 (R=H, R0=CH3) has been described in a patent.7
∗
†
Corresponding author.
E-mail: blanda@uni-wuppertal.de
0957-4166/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(98)00090-1

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H.-J. Altenbach, G. Blanda / Tetrahedron: Asymmetry 9 (1998) 1519–1524
Scheme 1.
2. Results and discussion
Methyl 1-benzyl-1,2,3,6-tetrahydropyridine-3-carboxylate8 3 was synthesised starting from the com-
mercially available β-keto ester 2 using the Shapiro reaction for the introduction of the double bond.9 In
accordance with the results of P. L. Fuchs and C. A. Bunnell,9 who have investigated the Shapiro reaction
of carbocyclic β-keto esters, only one regioisomer was formed in 73% yield. Reduction of the ester 3
with LiAlH4, followed by protection with Ac2O in pyridine gave the acetate 4 in nearly quantitative
yield. As the carbamate protecting group proved to be superior to the benzyl group with respect to
the determination of the enantiomeric purity, the benzyl protected compound 4 was transformed to the
carbamate 5 by treatment with phenoxycarbonyl chloride.10 On hydrolysis with sodium hydroxide in
ethanol the alcohol 6 could be prepared from 5 (Scheme 2).
Although the successful enzymatic resolution of racemic primary alcohols is rather rare,11 we were
encouraged by some recent work in this area12,13 to try lipase catalysed esterfication or hydrolysis for
this purpose, especially as B. Wirtz and W. Walther had reported that a saturated derivative of 1, t-butyl-
3-(hydroxymethyl)-piperidinecarboxylate, could be resolved efficiently using lipase from Pseudomonas
fluorescens.12
In screening experiments with the unsaturated system 5 and 6 lipase P from Pseudomonas caepacia
(PCL) showed the best enantiomeric excess of all the tested enzymes.14
The enantioselective esterification of the racemic alcohol 6 using PCL in hexane/CH2Cl2 in the
presence of vinyl butyrate delivered the butyryl ester (+)-8 in 33% yield with an enantiomeric excess
of 93% ee (determined by HPLC).15 The enantiomeric ratio16 E of the reaction was 42.
The inverse reaction, the enantioselective hydrolysis, using the same enzyme in a phosphate buffer,
led to the enantiomeric acetate (−)-7 in 94% ee17 (determined by HPLC) after 58% conversion with an
E value of 19.
The absolute configurations of the ester 7 and 8 were determined by chemical correlation to the known
(R)-3-(hydroxymethyl)piperidine,18 which was obtained from (+)-8 by reduction of the double bond with
H2/Pd–C, followed by a hydrolysis with aq. sodium hydroxide.
3. Conclusion
As a result of our studies an easy preparation of the formerly unknown building blocks (R)-3-
acetoxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate (−)-7 and phenyl (S)-3-butyryl-oxymethyl-3,6-
dihydro-2H-pyridine-1-carboxylate (+)-8 has been realised, which can permit the synthesis of isofagomin
derivatives and analogues in both enantiomeric forms by manipulation of the double bond.

H.-J. Altenbach, G. Blanda / Tetrahedron: Asymmetry 9 (1998) 1519–1524
1521
Scheme 2.
4. Experimental
4.1. General
The β-keto ester 2 was purchased from ACROS. Organic solvents were distilled before use or, if
otherwise noted, dried according to the typical procedures. All reactions were monitored by TLC prior
to work-up. TLC was run on silica plates 60 F254 (Merck) and visualised with UV fluorescence (254
1
and 366 nm) and/or molybdatophosphoric acid. H and 13C NMR were recorded on a Bruker ARX
400, specific rotation values on a Perkin–Elmer Polarimeter 241, mass spectra on a Varian MAT 311
and IR spectra on a Perkin–Elmer IR-Spectrometer 1420. High-performance liquid chromatography
analyses were performed using liquid chromatograph model Shimadzu 6a equipped with a Shimadzu
SPD-6a detector and DAICEL CHIRACEL OD column. Flash chromatography was performed on Merck
Kieselgel 60 (40–63 µm).

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H.-J. Altenbach, G. Blanda / Tetrahedron: Asymmetry 9 (1998) 1519–1524
4.2. Methyl-1-benzyl-1,2,3,6-tetrahydropyridine-3-carboxylate 3
To a solution of the β-keto ester 2 (11.0 g, 44.5 mmol) in dry CH2Cl2 (200 mL) p-
toluenesulfonylhydrazine (9.9 g, 53 mmol) was added under argon at room temperature. After
stirring for 2 days the reaction mixture was evaporated and the residue was dissolved in THF (160 mL).
At −78°C 155.8 mmol of LDA, prepared from diisopropylamine and n-butyllithium in THF at −20°C,
was added. The yellow solution became deep red, when warmed to room temperature. After 18 h
stirring at room temperature the mixture was poured into cold saturated NH4Cl (150 mL) and the layers
were separated. The aqueous phase was extracted with ether (2×120 mL) and the combined organic
portions were washed with H2O (150 mL) and brine (150 mL) and then dried (MgSO4). The solvent
was evaporated and the residue was purified by flash chromatography on silica gel (cyclohexane:ethyl
acetate=60:40) to yield the title compound 3 (7.5 g, 73%) as a yellow oil.
3
1H NMR (400 MHz, CDCl3): δ=2.95 (ABX, 1H, J=5.10 Hz, NCH2CH_CH), 3.04 (ABX, 1H,
3J=2.54 Hz, NCH2CH_CH), 3.36 (s, broad (br), 1H, CHCO2Me), 3.72 (s (br), 5H, CH2Ph, CH3),
2
3
3
2
2
5.87 (ABX, 1H, J=9.9 Hz, J=5.1 Hz, J=2.54 Hz, CH_CHCH), (ABX, 1H, J=9.9 Hz, J=4.6 Hz,
CH_CHCH), 7.35 (m, 5H, Ph). 13C NMR (100 MHz, CDCl3): δ=26.9 (t), 42.0 (d), 51.3 (t), 51.8 (q),
52.3 (t), 62.3 (t), 123.0 (d), 127.0 (d), 128.2 (d), 128.3 (d), 129.0 (d), 137.9 (s), 173.0 (s). IR [film]:
ν=1740 cm−1; ms (70 eV): 233 [M+]; C14H17NO2 (233.29). Calcd C 72.63, H 7.35, N 6.05, found C:
72.32, H 7.25, N 5.75.
4.3. 1-Benzyl-3-acetoxymethyl-1,2,3,6-tetrahydropyridine 4
A solution of methyl-1-benzyl-1,2,3,6-tetrahydropyridine-3-carboxylate 3 (2.7 g, 11.7 mmol) in dry
ether (70 mL) was added dropwise to a suspension of LiAlH4 (0.4 g, 11.7 mmol) in dry ether (30 mL)
at 0°C under an argon atmosphere. After 10 h, water (0.4 mL), 15% NaOH (0.4 mL) followed by more
water (1.3 mL) were successively added to the reaction mixture. The suspension was stirred for 30 min
and the precipitate was filtered off over Celite. The organic layer was dried (MgSO4) and evaporated.
The light yellow liquid was treated with pyridine (15 mL) and acetic anhydride (10 mL) at 0°C. After 5 h
the volatiles were removed on a rotary evaporator at 2×10−2 mbar and the residue was purified by flash
chromatography on silica gel (cyclohexane:ethyl acetate=80:20) to yield the acetate 4 (2.7 g, 93%) as a
1
yellow oil. H NMR (400 MHz, CDCl3): δ=2.02 (s, 3H, CH3), 2.20 (m, 1H, CHCH2O), 2.65, (m, 2H,
NCH2CHCH2O), 3.02, (m, 2H, NCH2CHCH), 3.64 (AB, 2H, 2J=13.23 Hz), 4.09 (ABX, 2H, Jab=10.68
Hz, CH2O), 5.68 (m, 1H, CHCHCH), 5.82 (ddd, 1H, 3J=1.52 Hz, 3J=3.05 Hz, 2J=11.71 Hz, CH2CHCH).
13C NMR (100 MHz, CDCl3): δ=20.8 (q), 35.9 (d), 51.7 (t), 52.8 (t), 62.4 (t), 65.9 (t), 125.0 (d), 127.1
(d), 127.6 (d), 128.2 (d), 129.0 (d), 138.1 (s), 170.9 (s). IR [film]: ν=1750 cm−1, 1250 cm−1, 1040 cm−1
;
ms (70 eV): 245 [M+]; C15H19NO2 (245.32).
4.4. Phenyl-3-acetoxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate 5
To a solution of the 1-benzyl-3-acetoxymethyl-1,2,3,6-tetrahydropyridine 4 (2.0 g, 8.1 mmol) in dry
toluene was added phenoxycarbonyl chloride (1.4 g, 8.94 mmol). The reaction mixture was heated under
reflux for 18 h and then the volatiles were evaporated on a rotary evaporator at 2×10−2 mbar. The
residue was purified by flash chromatography on silica gel (cyclohexane:ethyl acetate=70:30) to yield
the carbamate 5 (1.6 g, 72%) as a yellow oil. 1H NMR (400 MHz, CDCl3): δ=2.09 (s, 3H, CH3), 2.71
(s (br), 1H, CHCH2O), 3.77 (m (br), 2H, NCH2), 3.80 (m (br), 2H, NCH2), 4.09 (m, 2H, CHCH2O),
5.84 (m (br), 2H, CH2CH_CHCH), 7.23 (m, 5H, Ph). 13C NMR (100 MHz, CDCl3) two amide isomers:

H.-J. Altenbach, G. Blanda / Tetrahedron: Asymmetry 9 (1998) 1519–1524
1523
δ=21.0 (q), 34.9 (d), 35.2 (d), 42.9 (t), 43.5 (t), 44.0 (t), 64.7 (t), 64.9 (t), 121.9 (d), 125.1 (d), 125.7
(d), 126.1 (d), 126.9 (d), 129.4 (d), 151.1 (s). IR [film]: ν=1720–1750 cm−1; ms (70 eV): 275 [M+];
C15H17NO4 (275.30). Calcd C 65.38, H 6.18, N 5.09, found C 64.85, H 5.95, N 4.95.
4.5. Phenyl-3-hydroxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate 6
An alcoholic NaOH solution (0.2 N, 4 mL) was added over a period of 30 min to a stirred solution of
acetate 5 (1.1 g, 4 mmol) in dry EtOH (50 mL) under ice cooling. The resulting mixture was neutralised
with AcOH and extracted with CH2Cl2. The solvent was evaporated on a rotary evaporator at 2×10−2
mbar and purified by flash chromatography on silica gel (cyclohexane:ethyl acetate=60:40). The alcohol 6
was obtained as a yellow oil (0.8 g, 89%). 1H NMR (400 MHz, CDCl3): δ=2.53 (s (br), 2H, CHCH2OH),
3.59 (m, 2H, NCH2), 4.01 (m, 2H, NCH2), 4.27 (m, 2H, CH2OH), 5.81 (m, 2H, CH_CH), 7.30 (m, 5H,
Ph). 13C NMR (100 MHz, CDCl3) two amide isomers: δ=38.0 (d), 41.3 (t), 43.44 (t), 57.2 (t), 61.3 (t),
115.4 (d), 117.43 (d), 125.2 (d), 126.1 (d), 129.2 (d), 156.2 (s). IR [film]: ν=3400–3450 cm−1, 1690
cm−1; ms (70 eV): 232 [M+−H]; C13H15NO3 (233.30).
4.6. Phenyl (R)-3-acetoxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate (−)-7
A rapidly stirred suspension of (ꢀ)-phenyl-3-acetoxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate
(5) (0.5 g, 1.8 mmol) in phosphate buffer (7 mL, pH 7) containing lipase from Pseudomonas caepacia (30
mg) was maintained at pH 7 by automatic titration with NaOH (1 N). The reaction mixture was filtered
after 58% conversion over Celite and extracted with ethyl acetate (3×50 mL). The combined organic
extracts were dried (MgSO4) and evaporated. The crude product was purified by flash chromatography
on silica gel (cyclohexane:ethyl acetate=70:30) to yield the acetate (−)-7 (0.2 g, 40%) as a yellow oil.
1
The enantiomeric excess was determined by HPLC (heptane:isopropanol=90:10) to be 94%. H NMR
(400 MHz, CDCl3): δ=2.09 (s, 3H, CH3), 2.71 (s (br), 1H, CHCH2O), 3.77 (m (br), 2H, NCH2), 3.80
(m (br), 2H, NCH2), 4.09 (m, 2H, CHCH2O), 5.84 (m (br), 2H, CH2CH_CHCH), 7.23 (m, 5H, Ph). 13
C
NMR (100 MHz, CDCl3) two amide isomers: δ=21.0 (q), 34.9 (d), 35.2 (d), 42.9 (t), 43.5 (t), 44.0 (t),
64.7 (t), 64.9 (t), 121.9 (d), 125.1 (d), 125.7 (d), 126.1 (d), 126.9 (d), 129.4 (d), 151.1 (s); ms (70 eV):
275 [M+]; C15H17NO4 (275.30). IR [film]: ν=1720–1750 cm−1. Calcd C 65.38, H 6.18, N 5.09, found C
64.85, H 5.95, N 4.95.
4.7. Phenyl (S)-3-butyryloxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate (+)-8
To a rapidly stirred mixture of (ꢀ)-phenyl-3-hydroxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate
(5) (0.5 g, 2.1 mmol) in a small amount of CH2Cl2 and hexane (8 mL) lipase from Pseudomonas caepacia
(30 mg), vinyl butyrate (1.20 g, 10.5 mmol) was added. After 33% conversion (detected by HPLC)
the reaction mixture was filtered off over Celite and the solvent was evaporated. The crude product
was purified on silica gel using cyclohexane:ethyl acetate (80:20) to give the title compound as a light
yellow oil (0.2 g, 30%). The enantiomeric excess was determined by HPLC (heptane:isopropanol=90:10)
1
to be 93%. H NMR (400 MHz, CDCl3): δ=1.00 (t, 3H, CH3), 1.70 (s, 2H, CH2CH3), 2.38 (q, 2H,
CH2CH2CH3), 3.75 (s (br), 1H, CHCH2O), 3.76 (m (br), 2H, NCH2), 4.31 (m, 4H, NCH2 and CHCH2O),
5.83 (m (br), 2H, CH2CH_CHCH), 7.27 (m, 5H, Ph). 13C NMR (100 MHz, CDCl3): δ=13.6 (q), 18.4
(t), 34.8 (d), 35.1 (d), 36.1 (t), 42.4 (t), 42.7 (t), 43.4 (t), 43.8 (t), 64.2 (t), 64.5 (t), 121.6 (d), 125.0 (d),
125.3 (d), 125.8 (d), 126.6 (d), 129.2 (d), 151.3 (s), 173.4 (s). [α]20=+44; (c 2.66, CH2Cl2). IR [film]:
D

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H.-J. Altenbach, G. Blanda / Tetrahedron: Asymmetry 9 (1998) 1519–1524
ν=1720 cm−1; ms (70 eV): 303 [M+]; C17H21NO4 (303.35). Calcd C: 67.25, H 6.92, N 4.62, found C
66.73, H 6.90, N 4.03.
Acknowledgements
A Scholarship (Cusanus-Werk) for G. B. is gratefully acknowleged. We would like to thank the
following companies for support of the utilised enzymes: Novo Nordisk A/S, Meito Sangyo Co. and
Amano Pharmaceuticals Co.
References
1. (a) Le Merrer, Y.; Poitout, L.; Depezay, J.-C.; Dosbaa, I.; Geoffroy, S.; Foglietti, M.-J. Bioorg. Med. Chem. 1997, 5, 519.
(b) Huwe, C. M.; Blechert, S. Synthesis 1997, 61. (c) Johns, B. A.; Pan, Y. T.; Elbein, A. D.; Johnson, C. R. J. Am. Chem.
Soc. 1997, 119, 4856. (d) Carretero, J. C.; Arrayas, R. G.; Storch de Gracia, I. Tetrahedron Lett. 1997, 38, 8537. (e)
Brandstetter, T. W.; Davis, B.; Hyett, D.; Smith, C.; Hackett, L.; Winchester, B. W.; Fleet, G. W. J. Tetrahedron Lett. 1995,
36, 7511. (f) Look, G. C.; Fotsch, C. H.; Wong, C.-H. Acc. Chem. Res. 1993, 26, 182.
2. (a) Winchester, B.; Fleet, G. W. Glycobiology 1992, 2, 199, and references cited therein. (b) Kausal, G. P.; Elbein, A. D.
Trends Gycosci. Glycotechnol. 1993, 5, 209. (c) Sinnott, M. L Chem. Rev. 1990, 90, 1171.
3. Tsuruoka, T.; Fukuyasu, H.; Ishii, M.; Usui, T.; Shibahara, S.; Inouye, S. J. Antibiotics 1996, 9, 155.
4. Fleet, G. W. J.; Karpas, A.; Dwek, R. A.; Fellows, L. E.; Tyms, A. S.; Petrrsson, S.; Namgoong, S. K.; Ramsden, N. G.;
Smith, P. W.; Chan Son, J.; Wilson, F.; Witty, D. R.; Jacob, G. S.; Rademacher, T. W.; FEBS Lett. 1988, 237, 128.
5. (a) Jerpersen, T. M.; Dong, W.; Sierks, M. R.; Skrydstrup, T.; Lundt, I.; Bols, M. Angew. Chem. 1994, 106, 1858. (b)
Ichikawa, M.; Ichikawa, Y. Tetrahedron Lett. 1995, 36, 4585.
6. (a) Ref. 5. (b) Jerspersen, T. M.; Bols, M.; Sierks, M. R.; Skrydstrup, M. R. Tetrahedron 1994, 50, 13449. (c) Bols, M.
Tetrahedron Lett. 1996, 37, 2097. (d) Hansen, A.; Tagmose, T. M.; Bols, M. Chem. Commun. 1996, 2649. (e) Jerpersen,
T.; Dong, W.; Sierks, M. R.; Skrydstrup, T.; Bols, M. Biochemistry 1996, 35, 2788. (f) Hansen, A.; Tagmose, T. M.; Bols,
M. Tetrahedron 1997, 53, 697. (g) Ichikawa, M.; Ichikawa, Y. Bioorg. Med. Chem. 1995, 3, 161.
7. Treves, G.; Baum, B.; Burton, M. (FMC Corp.), U.S. patent 4467095 A, 1984 [Chem. Abstr. 1984, 101, 211000s].
8. (a) Allan, R. D.; Fong, J. Aust. J. Chem. 1983, 36, 601. (b) Müller-Uri, C.; Singer, E. A.; Fleischhacker, W. J. Med. Chem.
1986, 29 , 125. (c) Clinch, K.; Marquez, C. J.; Parrott, M. J.; Ramage, R. Tetrahedron 1989, 45, 239.
9. Bunnell, C. A.; Fuchs, P. L. J. Am. Chem. Soc. 1977, 99, 5184.
10. (a) Wright, W. B.; Brabander, H. J. J. Org. Chem. 1961, 26, 4057. (b) Oediger, H.; Joop, N. Liebigs Ann. Chem. 1972, 764,
21.
11. However, there are many examples of enzyme catalysed enantiotopos-differentiating acylation of prochiral primary diols
or of enzyme catalysed enantiotopos-differentiating hydrolysis of prochiral primary diol diacetates. See: (a) Drauz, K.;
Waldmann, H. Enzyme Catalysis in Organic Synthesis, VCH, Weinheim; 1995. (b) Weissfloch, A. N. E.; Kazlauskas, R. J.
J. Org. Chem. 1995, 60, 6959.
12. Wirtz, B.; Walther, W. Tetrahedron: Asymmetry 1992, 3, 1049.
13. For successful enzymatic resolutions in related 5-membered systems see: (a) Altenbach, H.-J.; Merhof, G. F.; Brauer, D.
J. Tetrahedron: Asymmetry 1996, 7, 2493. (b) Schieweck, F.; Altenbach, H.-J. Tetrahedron: Asymmetry 1998, 9, 403.
14. Screening with enzymes from Candida antartica (Novozym 435), Candida cylindracae (Sigma), Candida cylindracae
(Meito MY), Pseudomonas caepacia Amano PS), Pseudomonas fluorescens (Fluka), Aspergillus oryzae (Lipozym IM),
Pseudomonas species (Amano AK), Alcaligens species (Meito PL), Acromobacter species (Meito AL), pig pancreas lipase
(Type II, Aldrich) and pig liver esterase.
15. [α]2D0=+44; (c 2.66, CH2Cl2). HPLC: Chiracel OD-column (DAICEL Chemical Industry); heptane:ispropanol=90:10.
16. Chen, C. S.; Fujimoto, Y.; Girdaukas, G.; Shih, C. J. J. Am. Chem. Soc. 1982, 104, 7294.
17. [α]2D0=−60 (c 1.23; CH2Cl2). HPLC: Chiracel OD-column (DAICEL Chemical Industry); heptane:ispropanol=90:10.
18. Bettoni, G.; Duranti, E.; Tortorella, V. Gazz. Chim. Ital. 1972, 102, 189.