A nitro sugar-mediated stereocontrolled synthesis of β2- amino acids: Synthesis of a polyhydroxylated trans-2-aminocyclohexanecarboxylic acid

Article abstract of DOI:10.1002/ejoc.201200103

The first stereocontrolled nitro sugar-mediated synthesis of polyhydroxylated β-amino acids and their incorporation into peptides is described. The key steps of this approach are a Michael addition of the lithium salt of tris(phenylthio)methane (a carboxy

Full text of DOI:10.1002/ejoc.201200103

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FULL PAPER
DOI: 10.1002/ejoc.201200103
A Nitro Sugar-Mediated Stereocontrolled Synthesis of β2-Amino Acids:
Synthesis of a Polyhydroxylated trans-2-Aminocyclohexanecarboxylic Acid
José M. Otero,*[a,b] Fernando Fernández,[a,b] Juan C. Estévez,[a,b] Robert Nash,[c] and
Ramón J. Estévez*[a,b]
Dedicated to the memory of Professor Rafael Suau
Keywords: Amino acids / Carbohydrates / Michael addition / Protein engineering / Peptidomimetics / Inhibitors
The first stereocontrolled nitro sugar-mediated synthesis of
polyhydroxylated β-amino acids and their incorporation into
peptides is described. The key steps of this approach are a
Michael addition of the lithium salt of tris(phenylthio)meth-
ane (a carboxyl synthetic equivalent) to sugar nitro olefins,
and the reduction of the nitro group to an amino group.
Specifically, two glyceraldehyde-based β-amino acids and a
polyhydroxylated cyclohexyl β-amino acid were prepared.
The latter, which could act as a water-soluble mimic of the
proline-glycine δ-turn, was easily transformed into the corre-
sponding
5-amino-6-(hydroxymethyl)cyclohexane-1,2,3,4-
tetraol, a novel amino-carbasugar. However, this did not
show significant glycosidase inhibiting properties.
new drugs that overcome the pharmacological limitations
of proteins.[2]
Introduction
Research on proteins is of considerable chemical interest,
but the potential range of applications of these materials is
limited by the reduced number of secondary structures and
backbones resulting from the small number of proteinog-
enic amino acids. Moreover, the use of proteins as drugs is
limited by their easy enzymatic degradation and by their
side effects, which, in turn, have been related to their con-
formational flexibility.[1] One area of increasing interest
concerns peptidomimetics, and a great deal of work has
been carried out in recent years aimed at the synthesis of
non-natural amino acids that mimic the secondary structure
of natural peptide sequences. This constitutes the first step
in the introduction of elements of variety for the develop-
ment of peptidomimetics with high levels of diversity. Such
systems may be capable of generating highly ordered struc-
tures that improve on the recognition and catalytic proper-
ties of natural peptides and these compounds may act as
The most widely studied peptidomimetics are oligomers
of β-amino acids, which have been shown to adopt a range
of stable secondary structures such as α-helices, β-turns and
β-sheets. These characteristics facilitate interactions with re-
ceptors and enzymes and prevent peptidase degradation.[3]
Within this field, alicyclic β-amino acids are currently of
considerable interest as stabilisers of peptide conformations,
a property that has been related to the high tendency of
their homopolymers to fold in rigid secondary structures
over short peptide sequences.[4] Accordingly, there has re-
cently been a great deal of interest in the enantioselective
synthesis of β-amino acids. However, although there are nu-
merous routes to achiral β2-amino acids, their EPC (enan-
tiomerically pure compound) synthesis is currently the sub-
ject of numerous investigations.[5] Research in this field is
driven by the importance of these compounds. In fact, it
has been shown that the inclusion of β2-amino acids in
peptides or in naturally occurring compounds leads to enti-
ties that, in some cases, show cytotoxic or antiviral ac-
tivity.[5,6] Moreover, these β-peptides can adopt novel and
unique folding patterns.[3a]
[a] Centro Singular de Investigación en Química Biológica y
Materiales Moleculares (CIQUS), Universidad de Santiago de
Compostela,
15782 Santiago de Compostela, Spain
Fax: +34-881-815-704
Nitro olefins are powerful Michael acceptors that have
received considerable attention because of their special
chemical properties.[7] These compounds are readily at-
tacked by a wide range of nucleophiles to produce nitro-
alkanes bearing a chiral centre at position two, a fact that
makes them powerful tools for the construction of C–C
bonds by addition of organometallics to the electron-de-
E-mail: jose.otero@usc.es
ramon.estevez@usc.es
[b] Departamento de Química Orgánica, Facultad de Química,
Universidad de Santiago de Compostela,
15782 Santiago de Compostela, Spain
[c] Phytoquest Limited, IBERS,
Plas Gogerddan, Aberystwyth, Ceredigion, UK
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200103.
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ficient double bond. After the addition reaction, the nitro (Scheme 1). The structure of 2a was unambiguously estab-
group can be transformed into a diverse range of function- lished by X-ray diffraction.[15] The observed stereoselecti-
alities (amines, oximes, ketones, carboxylic acids, etc.) to vity was attributed to the chirality of the dioxolane subunit
provide a wide range of chemical compounds.[8] This versa- of 1a, which allows attack by the bulky tris(phenylthio)-
tile chemical protocol has recently been applied to the enan- methyl anion on the less hindered face of the olefinic double
tioselective preparation of β2-amino acids by addition of bond only. Treatment of 2a with HgO and BF3·OEt2 in a
organometallics to 3-nitropropenoates[9] and to 3,3-dialk- MeOH/THF/H2O mixture directly provided β-nitro ester 3a
oxy-1-nitroprop-1-enes[10] with asymmetric catalysis, fol- because spontaneous esterification of the carboxyl group
lowed by reduction of the resulting 2-substituted 3-nitro- occurred after hydrolysis of the tris(phenylthio)methyl resi-
derivatives and subsequent generation of their respective due.[17] β-Nitro ester 3a was subsequently reduced by cata-
carboxylic acid moieties. A variant of this strategy involves lytic hydrogenation with Pd-C and the resulting amino ester
conjugate addition of organometallics to optically active ni- was directly subjected to a peptide coupling protocol with
troalkenes, such as 2,2-dimethyl-4-[(E)-2-nitrovinyl]-1,3-di- benzyloxycarbonylglycine, TBTU and DIPEA to give the
oxolanes. These compounds are synthetic equivalents of ni- expected dipeptide 4a. Finally, the desired tripeptide 5a was
troacrylates and have proven to be versatile precursors for easily obtained by coupling of a second glycine unit to the
the synthesis of enantiopure β-amino acids in which the carboxyl moiety of this dipeptide.
nitro group is again a precursor for the amino functionality
Additionally, when nitro olefin 1b[18] was subjected to a
and the dioxolanyl side chain provides the carboxylic acid protocol similar to that described for 1a, tripeptide 5b (the
moiety by glycol cleavage.[11] An alternative that involves enantiomer of 5a) was also easily obtained in good yield
the addition of synthetic equivalents of carboxyl groups to and with good stereoselectivity via intermediate com-
electron-deficient nitroalkenes remains practically unex- pounds 2b, 3b and 4b (Scheme 1).
plored. To the best of our knowledge, only a few examples
of this approach have been described and they involve an
organocatalytic asymmetric addition of 2,4-pentadione[12]
or 1,3-dithiane[13] to nitro olefins. Following these additions,
long reaction sequences are required to generate the carboxyl
functionality of the corresponding β-amino acids. Moreover,
the preparation of β-amino acids involving the addition of
the lithium salt of tris(phenylthio)methane (a bulky carboxyl
synthetic equivalent)[14] to optically active nitro olefins had
not been described prior to our preliminary communication.
In this approach, the nitro group facilitates early introduc-
tion of the carboxyl group of the amino acid moiety by
Michael addition, and reduction of the nitro group provides
the amino group of the desired β-amino acid.[15] We report
here a full description of the synthesis of β-amino acids in-
corporated into dipeptides 4a and 4b and polyhydroxylated
cyclohexyl β-amino acid derivative 12.
Synthesis of Polyhydroxylated Cyclohexyl β-Amino Acid
This simple and efficient stereocontrolled access to
sugar-based β2-amino acids seems to be general in scope.
In fact, as part of an ongoing project aimed at extending
this approach to the plethora of tetroses, pentoses and
hexoses to gain access to a wide range of novel sugar and
carbasugar β-amino acids, the synthesis of the polyhy-
droxylated cyclohexyl β-amino acid derivatives 12 from d-
xylofuranose nitro olefin derivative 6 was carried out as de-
picted in Scheme 2.
The synthesis of a diverse set of polyhydroxylated cyclo-
hexyl β-amino acids is of vital importance for the develop-
ment of new β-peptides with useful functions, including
water soluble or liposoluble β-peptides, by protection or de-
protection of the hydroxyl groups present on their cyclohex-
ane rings.[3] Accordingly, these systems have become a key
topic in synthetic and medicinal chemistry and a variety
of procedures for their synthesis have been developed.[19]
However, the panel of known carbocyclic β-amino acids is
limited, probably due to the lack of efficient methods for
Results and Discussion
Synthesis of D- and L-Glyceraldehyde-Based β-Amino Acids
A stereocontrolled Michael addition of the lithium salt the stereocontrolled preparation of their polysubstituted de-
of tris(phenylthio)methane to nitro olefin 1a[16] resulted in rivatives, particularly polyhydroxylated derivatives, which
the exclusive formation of adduct 2a in 90% yield remains a salient challenge for synthetic chemists. Previous
Scheme 1. Synthesis of d- and l-glyceraldehyde-based β-amino acids. Reagents and conditions: (a) (PhS)3CH, nBuLi, THF, –78 °C, 15 min,
90% yield; (b) HgO, BF3·OEt2, MeOH/THF/H2O, room temp., 48 h, 66% yield; (c) i. H2 (1 atm), Pd-C (10%), AcOEt, room temp., 4 h,
68% yield; ii. CbzGlyOH, TBTU, DIPEA, CH2Cl2, room temp., 12 h, 62% yield; (d) i. Ba(OH)2·(H2O)8, THF/H2O, room temp., 30 min,
90% yield; ii. HGlyOMe·HCl, HATU, DIPEA, CH2Cl2, room temp., 12 h, 69% yield.
2
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Stereocontrolled Synthesis of β2-Amino Acids
Scheme 2. Synthesis of polyhydroxylated cyclohexyl β-amino acid. Reagents and conditions: (a) (PhS)3CH, nBuLi, THF, –78 to 0 °C, 4 h,
73% yield, 79% de; (b) HgO, BF3·OEt2, MeOH/H2O/CH2Cl2, room temp., 3 d, 82% yield; (c) TFA, H2O, room temp., 5 h; (d) NaHCO3,
MeOH/H2O, room temp., 12 h, 85% yield, 66% de; (e) 2,2-dimethoxypropane, PTSA, acetone, room temp., 24 h, 86% yield; (f) i. H2
(1 atm), Pd-C (10%), citric acid, MeOH, room temp., 2 d; ii. CbzCl, NaHCO3, MeOH/H2O, room temp., 3 h, 71% yield.
syntheses of di- and trihydroxylated cyclohexyl β-amino ac-
ids and a tetrahydroxylated cyclohexyl β-amino acid are of
limited scope because they involve construction of the cy-
clohexane ring by means of Diels–Alder reactions, a route
that requires resolution of the cycloadduct mixtures.[20] Our
present approach to the synthesis of polyhydroxylated cy-
clohexyl β-amino acids from nitro sugars is exemplified by
the easy transformation of nitro-xylofuranose derivative 6
(Scheme 2) into tripeptide 17 (Scheme 4) by a sequence sim-
ilar to those used for 5a and 5b. In this approach, the nitro
group facilitates a similar early introduction of the carboxyl
group and subsequent construction of the cyclohexane ring state. Thermal ellipsoids are drawn at the 50% probability level for
Figure 1. Molecular structures of compounds 7 and 11 in the solid
non-hydrogen atoms. Hydrogen atoms are represented by spheres
of arbitrary size.
of compounds 10a and 10b by an intramolecular Henry re-
action.[21]
Reaction of the easily prepared nitro-xylofuranose deriv-
ative 6[22] with lithium tris(phenylthio)methane at low tem- ment with aqueous trifluoroacetic acid gave an unstable
perature gave diastereoisomer 7 (79% diastereomeric ex- mixture of compounds 9, which was directly reacted with
cess) as a result of the preferred attack of the tris(phenyl- sodium hydrogen carbonate to give an inseparable 5:1 epi-
thio)methyl anion on the less hindered face of the double meric mixture of nitrocyclohexanes 10a and 10b resulting
bond of the Felkin–Anh favoured conformation of the from an intramolecular Henry reaction (Scheme 3). The ob-
starting nitro olefin 6.[23] Compound 7 was easily and ef- tained stereoselectivity can be explained by assuming that
ficiently isolated from the reaction mixture by crystallisa- this reversible cyclisation is subject to thermodynamic con-
tion and its structure was unambiguously established by X- trol and that the conformationally more stable muco-deriva-
ray crystallographic analysis (Figure 1).[24]
Hydrolysis of the tris(phenylthio)methyl subunit of 7 tive 10b at the equilibrium stage.[25]
tive 10a is more abundant than the less stable chiro-deriva-
with HgO and BF3·OEt2 provided the key β-nitro ester 8,
Attempts to improve the de of the cyclization through
which has a suitable carbon skeleton and functionality for the use of stronger inorganic bases or organic bases (e.g.,
the preparation of the target cyclohexyl β-amino acid 12. sodium carbonate, tertiary amines etc.) led to worse re-
Removal of the acetonide protecting group of 8 by treat- sults.[26] Treatment of the 10a + 10b mixture with 2,2-di-
Scheme 3. Mechanism of intramolecular Henry reaction of nitronate 9a to give nitrocyclohexanes 10a and 10b.
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Scheme 4. Incorporation of β-amino acid 12 into a small peptide sequence. Reagents and conditions: (a) Ba(OH)2·(H2O)8, THF/H2O,
room temp., 1 h; (b) i. TBDMSCl, im, DMF, 80 °C, 15 h; ii. MeOH, room temp., 2 h, 75% yield from 12; (c) HGlyOMe·HCl, TBTU,
DIPEA, DMF, room temp., 12 h, 83% yield; (d) i. H2 (1 atm), Pd-C (10%), MeOH, room temp., 2 h; ii. CbzGlyOH, TBTU, DIPEA,
DMF, room temp., 6 h, 73% yield; (e) TFA, H2O, room temp., 2 d, 82% yield.
methoxypropane under acidic conditions gave a mixture of ditionally, coupling constants between protons at positions
11 and unaltered 10b as a result of the selective protection C-1 and C-6 and at positions C-4 and C-5 are J = 2.0 Hz
of the cis-1,2-diol system of 10a (Scheme 2). The major and 3.4 Hz, respectively. These data are consistent with an
component 11 was easily isolated by preparative axial disposition of either δ-, ε- and ζ-hydroxyl groups.
chromatography and was purified by crystallization. The Based on these conformations, we developed an energy-
structure of 11 was unambiguously established by X-ray dif- minimized model of the cyclohexanic β-amino acid (Fig-
fraction (Figure 1).[24] Reduction of the nitro group of 11 ure 2).[27] It was concluded that this new β-amino acid
by catalytic hydrogenation and simultaneous removal of the could have a θ-torsion angle of 65° and a distance between
benzyl group gave an amino acid ester, which was treated the N- and C-termini of 3.1 Å. Therefore, this molecule
with benzyloxycarbonyl chloride to give amino acid deriva- forms a tight and water-soluble turn that could be used to
tive 12, with orthogonally protected amino and acid groups. effectively introduce a reverse-turn conformation in the
The next part of our study concerned the incorporation construction of water-soluble peptide β-hairpins. Addition-
of amino acid 12 into tripeptide 17, via compounds 13, 14, ally, this turn could be used as a water-soluble mimic of the
15 and 16 (Scheme 4). Thus, treatment of 12 with barium proline-glycine δ-turn, in which the distance between the N-
hydroxide furnished the corresponding carboxylic acid 13, and C-termini is close to 3.3 Å.[28]
which was treated with excess tert-butyldimethylsilyl chlor-
ide to give amino acid 14 in 75% overall yield after the two
steps. Activation of the carboxylic acid group of 14 with O-
(benzotriazol-1-yl)-N,N,NЈ,NЈ-tetramethyluronium
tetra-
fluoroborate (TBTU) and subsequent reaction with glycine
methyl ester hydrochloride provided dipeptide 15 in 83%
yield. Removal of the benzyloxycarbonyl group of 15 by
catalytic hydrogenation resulted in the corresponding free
amine derivative, which was added to a TBTU-activated
benzyloxycarbonylglycine solution and stirred at room tem-
perature for six hours. Purification by column chromatog-
raphy provided tripeptide 16 in 73% overall yield. The mass
spectrum and elemental analysis data confirmed the molec-
ular mass of tripeptide 16, which was treated with trifluoro-
acetic acid to remove the hydroxyl protecting groups to give
tripeptide 17 in 82% yield. To the best of our knowledge,
this is the first reported peptidic fragment that incorporates
a tetrahydroxylated cyclohexanic β-amino acid. An exhaus-
tive NMR analysis of this compound showed diaxial cou-
Figure 2. Comparison of distance between the N- and C-termini
in an energy-minimized model of the cyclohexanic β-amino acid
fragment of 17 (grey, 3.1 Å) and crystallographic model of Gly-Pro
δ-turn (black, 3.3 Å).[28]
Synthesis and Biological Studies of Polyhydroxylated
Amino-carbasugar 20
Amino-carbasugars became biologically relevant com-
pling constants of protons in positions C-1 and C-2 (α- and pounds after validamine, valienamine and hydroxyvalid-
β-amino acid protons, respectively, J = 11.7 Hz) and in po- amine were first isolated by chemical or microbial degrada-
sitions C-2 and C-3 (β- and γ-amino acid protons, respec- tion of validamycins[29] and showed significant activity as
tively, J = 12.2 Hz). In this compound the amino, carboxyl glycomimetics,[30] carbohydrate mimetics[31] and glycosyd-
and γ-hydroxyl groups are in an equatorial disposition. Ad- ase inhibitors.[32]
4
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Stereocontrolled Synthesis of β2-Amino Acids
Table 1. Inhibitory activities of compound 20 against glycosidases. Percentage inhibition at 143 μg/mL, optimal pH and 27 °C.[a]
Enzyme
Source
pH
Inhibition (%)[b]
α-d-Glucosidase
α-d-Glucosidase
α-d-Glucosidase
Saccharomyces cerevisiae
Bacillus sterothermophilus
rice
6.8
6.8
4
NI
41
51
β-d-Glucosidase
almond
green coffee bean
bovine liver
bovine kidney
jack bean
Cellullomonas fimi
Penicillium decumbens
bovine kidney
jack bean
5
NI
NI
NI
NI
–6
–10
NI
NI
–8
α-d-Galactosidase
β-d-Galactosidase
α-l-Fucosidase
α-d-Mannosidase
β-d-Mannosidase
6.5
7.3
5.5
4.5
6.5
4
4.25
5
5
Naringinase
N-Acetyl-β-d-glucosaminidase
N-Acetyl-β-d-glucosaminidase
N-Acetyl-β-d-hexosaminidase
Amyloglucosidase
Aspergillus oryzae
Aspergillus niger
NI
11
4.5
[a] For conditions of measurements see ref.[34] and the Supporting Information. [b] NI denotes less than 5% inhibition.
In connection with our recent intensive work on the syn- (from d-glucose). These compounds constitute novel, at-
thesis of new and selective glycosidase inhibitors,[33] we re- tractive synthetic tools that offer new, unexplored opportu-
port here the easy transformation of β-amino acid deriva- nities to increase diversity in the field of β2-amino acids.
tive 12 into amino-carbasugar 20, a new analogue of valida- These amino acids were easily obtained from 3-nitropropi-
mine (Scheme 5).
onic acids by reduction of the nitro group to an amino
group. Accordingly, d-glyceraldehyde-derived 3-nitropropi-
onic ester 3a and l-glyceraldehyde-derived 3-nitropropionic
ester 3b were directly transformed into 3-aminopropionic
ester 4a and its enantiomeric β-amino acid ester 4b, respec-
tively. The more complex 2-glucosyl-3-nitropropionic ester
8 offers the opportunity to exploit the ability of nitro com-
pounds to form carbon–carbon bonds by the Henry reac-
tion prior to nitro-amino reduction. This protocol enabled
the preparation of the first reported 2,3,4,5-tetrahydroxy-
6-nitrocyclohexanecarboxylic acids (epimers 10a and 10b).
Reduction of the nitro group of epimer 11 to the amino
group led to the first reported trans-2-amino-3,4,5,6-tetra-
hydroxycyclohexanecarboxylic acid 12, which was easily in-
corporated into a tripeptide by coupling glycine units to its
amino and carboxyl moieties. On the other hand, tetrahy-
droxylated cyclohexane β-amino acid derivative 12 was eas-
ily converted into a novel 5-amino-6-(hydroxymethyl)-
cyclohexan-1,2,3,4-tetraol (20). Some of these amino-carba-
sugars show glycosidase inhibition properties, but, unfortu-
nately, this new analogue did not show significant activity.
Work is in progress on the design, synthesis and study of
the structural properties and applications of peptides incor-
porating cyclohexyl β-amino acid 12. Further explorations
on additional synthetic possibilities offered by 3-nitro-2-
glucosylpropionic acid ester, including transformation into
polyhydroxylated 2-aminocyclopentanecarboxylic acids,
aminocyclopentitols and iminocyclitols are ongoing.
Scheme 5. Synthesis of polyhydroxylated amino-carbasugar. Rea-
gents and conditions: (a) NaBH4, EtOH, room temp., 3 h, 86%
yield; (b) H2 (1 atm), Pd-C (10%), MeOH, room temp., 3 h, 98%
yield; (c) HCl, MeOH, 50 °C, 3 h, 92% yield.
Reaction of β-amino acid 12 with sodium borohydride
provided aminopolyol 18 in 86% yield. Catalytic hydrogen-
ation of 18 furnished derivative 19 in 98% yield through
removal of the benzyl- and benzyloxycarbonyl protecting
groups. Finally, treatment of 19 with aqueous HCl resulted
in the formation of amino-carbasugar 20, which was iso-
lated in 92% yield as its chlorhydrate salt.
The biological activity of novel amino-carbasugar 20 was
tested against
a panel of representative glycosidases
(Table 1), but significant inhibition was unfortunately not
observed. Despite this negative result, this methodology
would be of great interest to obtain new amino-carbasugars
from monosaccharides.
Conclusions
We have developed a promising synthesis of β-nitro-
propionic acids that allowed us to prepare the first three
examples of C-2-glycosyl 3-nitropropionic acids: methyl
(2S,3S)-3,4-(isopropylidendioxy)-2-(nitromethyl)butanoate
(3a) (from d-glyceraldehyde), methyl (2R,3R)-3,4-(isopro-
pylidenedioxy)-2-(nitromethyl)butanoate (3b) (from l-glyc-
eraldehyde) and 3-O-benzyl-5,6-dideoxy-1,2-O-isopropylid-
Experimental Section
General: All non-aqueous reactions were carried out under a posi-
tive atmosphere of argon in flame-dried glassware, unless otherwise
noted, with solvents purified according to ref.[35] Preparative flash
chromatography was performed using 60 Merck 230–400 mesh
(flash, 0.04–0.063) silica. Thin layer chromatography (TLC) was
ene-5-C-(methoxycarbonyl)-6-nitro-α-d-glucofuranose (8) carried out on aluminium-backed sheets coated with 60 GF254 sil-
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ica. Plates were developed by using a spray of 0.2% w/v cerium(IV)
sulfate and 5% ammonium molybdate in 2 m sulfuric acid. Melting
points were recorded with a Köfler hot block and are uncorrected.
1H and 13C NMR spectra were recorded with Bruker DPX 250
3.22 (dt, J2,1Јa = 8.0 Hz, J2,1Јb = J2,3 = 3.9 Hz, 1 H, 2-H), 1.42 (s,
3 H, CH3), 1.33 (s, 6 H, CH3) ppm. 13C NMR (62.5 MHz, CDCl3):
δ = 169.7, 109.6, 72.8, 72.2, 68.0, 52.4, 46.9, 26.1, 24.6 ppm. MS
(CI): m/z (%) = 234 (42) [M + H]+, 175 (100) [M – iPrO]+. IR
(250 MHz for 1H and 62.5 MHz for 13C), Varian Mercury 300 (NaCl): ν = 1731, 1551, 1375 cm–1. C9H15NO6 (233): calcd. C
˜
(300 MHz for 1H and 75 MHz for 13C) or Bruker DQX 400
(400 MHz for 1H and 100 MHz for 13C) spectrometers at room
temperature unless otherwise stated. All chemical shifts are quoted
on the δ-scale using residual solvent as internal standard; s, d, t, q,
m, and br. designate singlet, doublet, triplet, quartet, multiplet, and
broad, respectively. Coupling constants (J) are given in Hz. Low
resolution mass spectra were recorded with a Hewlett–Packard
5988A spectrometer (by chemical ionisation as stated). Infrared
spectra were recorded with an FTIR MIDAC Prospect spectropho-
tometer. Only characteristic peaks are quoted (wavenumbers, cm–1).
Optical rotations were measured with a Jasco DI-370 polarimeter
with a path length of 0.5 dm and a Na (589 nm) lamp; concentra-
tions are given in g/100 mL. Elemental analyses were obtained with
a Carlo–Erba EA 1108 analyser. X-ray diffraction was carried out
with a Nonius FR591-Kappa-CCD-2000 diffractometer or with a
Bruker Smart-CCD-100 diffractometer as stated.
46.35, H 6.48, N 6.01; found C 46.26, H 6.27, N 5.86.
Methyl (2S,3S)-2-{[2-(Benzyloxycarbonylamino)acetamido]methyl}-
3,4-(isopropylidendioxy)butanoate (4a). Typical Procedure III: Pal-
ladium on activated charcoal (10%, 0.011 g) was added to a de-
gassed solution of compound 3a (0.11 g, 0.47 mmol) in EtOAc
(5 mL) and the mixture was stirred under one atmosphere of hydro-
gen at room temp. for 4 h. Analysis by TLC (EtOAc/hexane, 1:4)
revealed that the starting material had been consumed. The reac-
tion mixture was filtered through a pad of Celite and concentrated
to dryness to give the corresponding amino intermediate, which
was dried under high vacuum. In a round-bottomed flask under
an argon atmosphere, a mixture of CbzGlyOH (0.08 g, 0.37 mmol),
TBTU (0.19 g, 0.59 mmol) and DIPEA (0.22 mL, 1.28 mmol) in
anhydrous CH2Cl2 (1 mL) was stirred at room temp. for 15 min. A
solution of amino intermediate in anhydrous CH2Cl2 (3 mL) was
added dropwise and, after 12 h stirring at room temp., TLC
(CH2Cl2/MeOH, 1:4) revealed that the starting material had been
consumed. The reaction mixture was washed with 10% aqueous
HCl (3 mL) and the organic layer was dried (Na2SO4), filtered and
concentrated to dryness. The residue was purified by column
chromatography (EtOAc/hexane, 2:1) to afford compound 4a
(0.08 g, 0.20 mmol, 42% yield) as a colourless oil; [α]2D7 = –14.7 (c
[(2S,3S)-3,4-Isopropylidendioxy-2-(nitromethyl)butane-1,1,1-triyl]-
tris(phenylsulfane) (2a). Typical Procedure I: A suspension of
(PhS)3CH (0.71 g, 2.08 mmol) in anhydrous THF (2.8 mL) was co-
oled to –78 °C under argon and nBuLi (1.44 mL, 1.99 mmol, 1.38 m
in hexanes) was added dropwise. The mixture was stirred for 1 h
and a solution of compound 1a (0.3 g, 1.73 mmol) in anhydrous
THF (1.7 mL) was added slowly during 15 min. Once the addition
was complete, TLC (EtOAc/hexane, 1:4) revealed that the starting
material had been consumed. The reaction was quenched by ad-
dition of saturated aqueous NH4Cl (10 mL) and the mixture was
extracted with CH2Cl2 (3ϫ10 mL). The combined organic layers
were dried (Na2SO4), filtered and concentrated to dryness. The re-
sulting residue was crystallized from CH2Cl2/MeOH to afford com-
1
= 1.2, CHCl3). H NMR (250 MHz, CDCl3): δ = 7.38–7.32 (m, 5
H, 5ϫH-Ph), 6.58 (br. s, 1 H, NH), 5.34 (br. s, 1 H, NH), 5.13 (m,
2 H, 2ϫCHPh), 4.37–4.29 (m, 1 H, 3-H), 4.12 (dd, J4b,4 = 8.5 Hz,
J4b,3 = 6.3 Hz, 1 H, 4-Hb), 3.85 (2 ϫ d, JHЈ,H = 5.8 Hz, 2 H,
2ϫCH-Gly), 3.77 (dd, J4a,4b = 8.5 Hz, J4a,3 = 6.0 Hz, 1 H, 4-Ha),
3.71 (s, 3 H, CH3O), 3.69–3.60 (m, 2 H, 1Ј-Ha + 1Ј-Hb), 2.75–2.65
(m, 1 H, 2-H), 1.41 (s, 3 H, CH3), 1.33 (s, 3 H, CH3) ppm. 13C
pound 2a (0.81 g, 1.57 mmol, 90% yield) as a colourless solid; m.p. NMR (62.5 MHz, CDCl3): δ = 171.9, 169.1, 156.5, 136.0, 128.3,
106–107 °C; [α]2D7 = –44.5 (c = 1.1, CHCl3). H NMR (250 MHz,
CDCl3): δ = 7.70–7.60 (m, 6 H, 6 ϫ H-Ph), 7.50–7.30 (m, 9 H,
9ϫH-Ph), 4.87 (dd, J1Јb,1Јa = 15.0 Hz, J1Јb,2 = 2.0 Hz, 1 H, 1Ј-Hb),
4.76–4.69 (m, 1 H, 3-H), 4.65 (dd, J1Јa,1Јb = 15.0 Hz, J1Јa,2 = 8.0 Hz,
128.1, 128.0, 127.9, 109.4, 74.5, 67.8, 66.9, 52.0, 48.6, 44.3, 38.1,
1
26.3, 24.9 ppm. MS (CI): m/z (%) = 395 (100) [M + H]+, 91 (62)
[CH Ph]+ . IR (NaCl): ν = 3335, 1731, 1676, 1530 cm–1
.
˜
2
C19H26N2O7 (395): calcd. C 57.86, H 6.64, N 7.10; found C 57.77,
1 H, 1Ј-Ha), 4.12 (dd, J4a,4b = 8.5 Hz, J4a,3 = 6.3 Hz, 1 H, 4-Ha), H 6.51, N 6.93.
3.47 (dd, J4b,4a = 8.5 Hz, J4b,3 = 6.8 Hz, 1 H, 4-Hb), 3.31 (ddd,
Methyl (S)-9-[(S)-1,2-Isopropylidendioxyethyl]-3,6,10-trioxo-1-
J2,1Јa = 8.0 Hz, J2,3 = 5.8, J2,1Јb = 2.0 Hz, 1 H, 2-H), 1.29 (s, 3 H,
CH3), 1.19 (s, 3 H, CH3) ppm. 13C NMR (62.5 MHz, CDCl3): δ =
136.0, 130.2, 129.7, 128.6, 108.8, 77.0, 73.8, 73.4, 70.7, 48.7, 25.1,
24.7 ppm. MS (CI): m/z (%) = 514 (20) [M + H]+, 498 (10) [M –
phenyl-2-oxa-4,7,11-triazatridecan-13-oate (5a). Typical Procedure
IV: Compound 4a (0.05 g, 0.13 mmol) was dissolved in a mixture
of THF/H2O (1:2, 6 mL) and Ba(OH)2·(H2O)8 (0.12 g, 0.38 mmol)
was added. The mixture was stirred at room temp. for 30 min.
Analysis by TLC (EtOAc/hexane, 2:1) showed that the starting ma-
terial had been consumed. The reaction mixture was neutralized
with acid resin, filtered and concentrated to dryness under high
vacuum. The crude product was dissolved in anhydrous CH2Cl2
(3 mL) and HATU (0.05 g, 0.15 mmol) and DIPEA (0.11 mL,
0.68 mmol) were added. The solution was stirred at room temp. for
15 min and HGlyOMe·HCl (0.02 g, 0.18 mmol) was added. After
stirring the mixture for 12 h at room temp., TLC (CH2Cl2/MeOH,
9:1) revealed that the starting material had been consumed. The
reaction mixture was diluted with CH2Cl2 (7 mL) and washed with
10% aqueous HCl (7 mL). The organic layer was dried (Na2SO4),
filtered and concentrated to dryness. The resulting residue was
purified by column chromatography (EtOAc) to afford compound
CH ]+, 404 (100) [M – SPh]+. IR (NaCl): ν = 1555, 1373 cm–1.
˜
3
C26H27NO4S3 (513): calcd. C 60.79, H 5.30, N 2.73, S 18.73; found
C 60.73, H 5.39, N 2.73, S 18.66.
(2S,3S)-Methyl 3,4-Isopropylidendioxy-2-(nitromethyl)butanoate
(3a). Typical Procedure II: Compound 2a (1.56 g, 3.04 mmol) was
dissolved in a mixture of MeOH/THF/H2O (10:1:0.25, 135 mL)
and HgO (1.98 g, 9.12 mmol) and BF3·Et2O (0.73 mL, 5.62 mmol)
were added. The mixture was stirred at room temp. for 48 h. Analy-
sis by TLC (EtOAc/hexane, 1:4) revealed that the starting material
had been consumed. The reaction mixture was filtered through a
pad of Celite and concentrated to dryness. The resulting residue
was purified by column chromatography (EtOAc/hexane, 1:9) to
afford compound 3a (0.47 g, 1.99 mmol, 66% yield) as a yellow oil;
[α]2D6 = –23.2 (c = 1.2, CHCl3). H NMR (250 MHz, CDCl3): δ =
5a (0.04 g, 0.08 mmol, 62% yield) as a colourless oil; [α]2D7 = –15.8
1
1
4.87 (dd, J1Јa,1Јb = 15.0 Hz, J1Јa,2 = 8.0 Hz, 1 H, 1Ј-Ha), 4.75 (dd, (c = 2.3, CHCl3). H NMR (250 MHz, CDCl3): δ = 7.39–7.31 (m,
J1Јb,1Јa = 15.0 Hz, J1Јb,2 = 3.9 Hz, 1 H, 1Ј-Hb), 4.37–4.29 (m, 1 H,
3-H), 4.21 (dd, J4b,4a = 8.7 Hz, J4b,3 = 6.0 Hz, 1 H, 4-Hb), 3.91
(dd, J4a,4b = 8.7 Hz, J4a,3 = 5.2 Hz, 1 H, 4-Ha), 3.77 (s, 3 H, CH3O),
5 H, 5ϫH-Ph), 7.13 (br. s, 2 H, 2ϫNH), 5.79 (br. s, 1 H, NH),
5.09 (m, 2 H, 2ϫCHPh), 4.35–4.13 (m, 2 H, 3-H + 4-Hb), 4.07–
3.85 (m, 3 H, 4-Ha + 2ϫCH-Gly), 3.77 (m, 2 H, 2ϫCH-Gly),
6
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20103
/KAP1
Date: 02-04-12 15:01:00
Pages: 12
Stereocontrolled Synthesis of β2-Amino Acids
3.71 (s, 3 H, CH3O), 3.74–3.67 (m, 1 H, 1Ј-Ha), 3.20–3.18 (m, 1 H, Methyl (R)-9-[(R)-1,2-Isopropylidendioxyethyl]-3,6,10-trioxo-1-
1Ј-Hb), 2.79–2.68 (m, 1 H, 2-H), 1.47 (s, 3 H, CH3), 1.34 (s, 3 H, phenyl-2-oxa-4,7,11-triazatridecan-13-oate (5b): According to typi-
CH3) ppm. 13C NMR (62.5 MHz, CDCl3): δ = 169.8, 169.5, 167.1, cal procedure IV, the reaction of compound 4b (0.05 g, 0.13 mmol)
147.4, 136.0, 128.5, 128.2, 128.0, 109.4, 74.9, 67.7, 67.2, 67.1, 52.4,
with Ba(OH)2·(H2O)8 (0.12 g, 0.38 mmol) in a mixture of THF/
H2O (1:2, 6 mL) and then with HATU (0.05 g, 0.15 mmol), DIPEA
(0.11 mL, 0.68 mmol) and H-Gly-OMe·HCl (0.02 g, 0.18 mmol) in
49.6, 44.6, 41.1, 39.4, 26.7, 25.2 ppm. MS (CI): m/z (%) = 452 (21)
[M + H]+, 91 (100) [CH Ph]+. IR (NaCl): ν = 3317, 1727, 1661,
˜
2
1538 cm–1. C21H29N3O8 (451): calcd. C 55.87, H 6.47, N 9.31; CH2Cl2 (3 mL) afforded compound 5b (0.03 g, 0.07 mmol, 58%
found C 56.18, H 6.30, N 9.54.
yield) as a colourless oil; [α]2D8 = +13.7 (c = 2.5, CHCl3). 1H NMR
(250 MHz, CDCl3): δ = 7.39–7.31 (m, 5 H, 5ϫH-Ph), 7.13 (br. s,
2 H, 2ϫNH), 5.79 (br. s, 1 H, NH), 5.09 (m, 2 H, 2ϫCHPh),
4.35–4.13 (m, 2 H, 3-H + 4-Hb), 4.07–3.85 (m, 3 H, 4-H + 2ϫCH-
Gly), 3.77 (m, 2 H, 2ϫCH-Gly), 3.71 (s, 3 H, CH3O), 3.74–3.67
(m, 1 H, 1Ј-Hb), 3.20–3.18 (m, 1 H, 1Ј-Ha), 2.79–2.68 (m, 1 H, 2-
H), 1.47 (s, 3 H, CH3), 1.34 (s, 3 H, CH3) ppm. 13C NMR
(62.5 MHz, CDCl3): δ = 169.8, 169.5, 167.1, 147.4, 136.0, 128.5,
128.2, 128.0, 109.4, 74.9, 67.7, 67.1, 52.4, 49.5, 44.6, 41.1, 39.4,
26.7, 25.2 ppm. MS (CI): m/z (%) = 452 (20) [M + H]+, 91 (100)
[(2R,3R)-3,4-Isopropylidendioxy-2-(nitromethyl)butane-1,1,1-triyl]-
tris(phenylsulfane) (2b): According to typical procedure I, the reac-
tion of 1b (0.42 g, 2.40 mmol) with (PhS)3CH (0.90 g, 2.64 mmol)
and nBuLi (1.65 mL, 2.64 mmol, 1.6 m in hexanes) in anhydrous
THF (6.3 mL) afforded compound 2b (1.1 g, 2.13 mmol, 88 %
yield) as a colourless crystalline solid; m.p. 108–109 °C (CH2Cl2/
MeOH); [α]2D8 = +43.0 (c = 1.2, CHCl3). 1H NMR (250 MHz,
CDCl3): δ = 7.70–7.60 (m, 6 H, 6 ϫ H-Ph), 7.50–7.30 (m, 9 H,
9ϫH-Ph); 4.87 (dd, J1Јb,1Јa = 15.0 Hz, J1Јb,2 = 2.0 Hz, 1 H, 1Ј-Hb),
4.76–4.69 (m, 1 H, 3-H), 4.65 (dd, J1Јa,1Јb = 15.0 Hz, J1Јa,2 = 8.0 Hz,
1 H, 1Ј-Ha), 4.12 (dd, J4a,4b = 8.5 Hz, J4a,3 = 6.3 Hz, 1 H, 4-H),
3.47 (dd, J4b,4a = 8.5 Hz, J4b,3 = 6.8 Hz, 1 H, 4-Hb), 3.31 (ddd,
J2,1Јa = 8.0 Hz, J2,3 = 5.8 Hz, J2,1Јb = 2.0 Hz, 1 H, 2-H), 1.29 (s, 3
H, CH3), 1.19 (s, 3 H, CH3), ppm. 13C NMR (62.5 MHz, CDCl3):
δ = 136.0, 130.2, 129.7, 128.6, 108.8, 77.0, 73.8, 73.4, 70.7, 48.7,
25.1, 24.7 ppm. MS (CI): m/z (%) = 514 (30) [M + H]+, 498 (33)
[M – CH ]+, 404 (100) [M – SPh]+. IR (NaCl): ν = 1555, 1373 cm–1.
[CH Ph]+ . IR (NaCl): ν = 3319, 1726, 1660, 1538 cm–1
.
˜
2
C21H29N3O8 (451): calcd. C 55.87, H 6.47, N 9.31; found C 56.15,
H 6.51, N 9.12.
3-O-Benzyl-5,6-dideoxy-1,2-O-isopropylidene-6-nitro-5-C-[tris(phen-
ylthio)methyl]-α-D-glucofuranose (7): According to typical pro-
cedure I, the reaction of 6 (2.10 g, 6.53 mmol) with (PhS)3CH
(2.71 g, 7.97 mmol) and nBuLi (5.0 mL, 7.63 mmol, 1.55 m in hex-
anes) in anhydrous THF (10 mL) at 0 °C during 4 h resulted, after
flash column chromatography (EtOAc/hexane, 1:5), in a mixture of
the α-d-glucofuranose derivative 7, as the main product, and the β-
l-idofuranose derivative, as a minor compound (3.77 g, 5.69 mmol,
87% yield, 79% de estimated by comparison of the intensity of H-
1 protons in NMR). Crystallization of this mixture from Et2O/
hexane provided pure 7 (2.03 g, 1.75 mmol, 73% yield) as a colour-
less crystalline solid; m.p. 132–134 °C (Et2O/hexane); [α]2D0 = –23.7
(c = 2.04, CHCl3). 1H NMR (300 MHz, CDCl3): δ = 7.68–7.65 (m,
5 H, 5ϫH-Ph), 7.40–7.28 (m, 12 H, 12ϫH-Ph), 7.17–7.14 (m, 3
H, 3ϫH-Ph), 5.82 (d, J1,2 = 4.0 Hz, 1 H, 1-H), 5.08 (dd, J3,4 = 3.3
Hz, J4,5 = 3.7 Hz, 1 H, 4-H), 4.85 (dd, J5,6 = 3.0 Hz, J6,6 = 15.5 Hz,
1 H, 6-H), 4.72 (dd, J5,6 = 6.1 Hz, J6,6 = 15.5 Hz, 1 H, 6-H), 4.44
(d, J1,2 = 4.0 Hz, 1 H, 2-H), 4.35 [d, JH,H = 11.9 Hz, 1 H, CH2Ph],
4.30 (d, JH,H = 11.9 Hz, 1 H, CH2Ph), 3.92 (ddd, J5,6 = 3.0 Hz,
J4,5 = 3.7 Hz, J5,6 = 6.1 Hz, 1 H, 5-H), 3.73 (d, J3,4 = 3.3 Hz, 1 H,
3-H), 1.53 (s, 3 H, CH3), 1.31 (s, 3 H, CH3) ppm. 13C NMR
(62.5 MHz, CDCl3): δ = 136.9, 136.4, 130.7, 129.7, 128.7, 128.3,
127.7, 127.6, 111.6, 104.4, 83.8, 81.8, 79.1, 78.2, 73.6, 71.7, 44.4,
27.1, 26.4 ppm. MS (CI): m/z (%) = 662 (1) [M + H]+, 552 (100)
˜
3
C26H27NO4S3 (513): calcd. C 60.79, H 5.30, N 2.73, S 18.73; found
C 60.59, H 5.11, N 2.62, S 18.52.
Methyl (2R,3R)-3,4-Isopropylidendioxy-2-(nitromethyl)butanoate
(3b): According to typical procedure II, the reaction of 2b (0.64 g,
1.25 mmol) with HgO (0.81 g, 3.75 mmol) and BF3·Et2O (0.3 mL,
2.31 mmol) in a mixture of MeOH/THF/H2O (10:1:0.25, 45 mL)
afforded compound 3b (0.2 g, 0.86 mmol, 69% yield) as a yellow
oil; [α]2D7 = +24.3 (c = 1.2, CHCl3). H NMR (250 MHz, CDCl3):
1
δ = 4.87 (dd, J1Јa,1Јb = 15.0 Hz, J1Јa,2 = 8.0 Hz, 1 H, 1Ј-Ha), 4.75
(dd, J1Јb,1Јa = 15.0 Hz, J1Јb,2 = 3.9 Hz, 1 H, 1Ј-Hb), 4.37–4.29 (m,
1 H, 3-H), 4.21 (dd, J4b,4a = 8.7 Hz, J4b,3 = 6.0 Hz, 1 H, 4-Hb),
3.91 (dd, J4a,4b = 8.7 Hz, J4a,3 = 5.2 Hz, 1 H, 4-Ha), 3.77 (s, 3 H,
CH3O), 3.22 (dt, J2,1Јa = 8.0 Hz, J2,1Јb = J2,3 = 3.9 Hz, 1 H, 2-H),
1.42 (s, 3 H, CH3), 1.33 (s, 6 H, CH3) ppm. 13C NMR (62.5 MHz,
CDCl3): δ = 169.7, 109.6, 72.8, 72.2, 68.0, 52.4, 46.9, 26.1,
24.6 ppm. MS (CI): m/z (%) = 234 (29) [M + H]+, 175 (100) [M –
iPrO]+. IR (NaCl): ν = 1732, 1555, 1375 cm–1. C H NO (233):
˜
9
15
6
calcd. C 46.35, H 6.48, N 6.01; found C 46.12, H 6.52, N 6.22.
Methyl (2R,3R)-2-{[2-(Benzyloxycarbonylamino)acetamido]methyl}-
3,4-(isopropylidendioxy)butanoate (4b): According to typical pro-
cedure III, the reaction of 3b (0.20 g, 0.86 mmol) with 10% palla-
dium on activated charcoal (0.02 g) in EtOAc (8 mL) and then with
Cbz-Gly-OH (0.18 g, 0.86 mmol), TBTU (0.37 g, 1.14 mmol) and
DIPEA (0.5 mL, 2.87 mmol) in anhydrous CH2Cl2 (3 mL) afforded
compound 4b (0.14 g, 0.35 mmol, 41% yield) as a colourless oil;
[M – PhS]+, 505 (23) [M – C H NO S]+. IR (NaCl): ν = 1556,
˜
6
6
2
1381 cm–1. C35H35NO6S3 (661): calcd. C 63.52, H 5.33, N 2.12, S
14.53; found C 63.71, H 5.51, N 2.17, S 14.75.
3-O-Benzyl-5,6-dideoxy-1,2-O-isopropylidene-5-C-(methoxycarb-
onyl)-6-nitro-α-D-glucofuranose (8): According to typical procedure
II, the reaction of 7 (1.57 g, 2.38 mmol) with HgO (1.55 g,
7.14 mmol) and BF3·Et2O (0.36 mL, 2.86 mmol) in a mixture of
[α]2D7 = +15.3 (c = 1.2, CHCl3). H NMR (250 MHz, CDCl3): δ =
1
7.38–7.32 (m, 5 H, 5ϫH-Ph), 6.58 (br. s, 1 H, NH), 5.34 (br. s, 1 MeOH/CH2Cl2/H2O (12:1:1.5, 115 mL) at room temp. during three
H, NH), 5.13 (m, 2 H, 2ϫCHPh), 4.37–4.29 (m, 1 H, 3-H), 4.12
(dd, J4b,4 = 8.5 Hz, J4b,3 = 6.3 Hz, 1 H, 4-Hb), 3.85 (2ϫd, JHЈ,H
5.8 Hz, 2 H, 2ϫCH-Gly), 3.77 (dd, J4a,4b = 8.5 Hz, J4a,3 = 6.0 Hz,
days afforded compound 8 (0.74 g, 1.94 mmol, 82% yield) as a yel-
low oil after column chromatography (EtOAc/hexane, 1:8 Ǟ 1:3.5);
=
1
[α]2D0 = –52.4 (c = 1.21, CHCl3). H NMR (250 MHz, CDCl3): δ =
1 H, 4-Ha), 3.71 (s, 3 H, CH3O), 3.69–3.60 (m, 2 H, 1Ј-Ha + 1Ј- 7.41–7.26 (m, 5 H, 5ϫH-Ph), 5.86 (d, J1,2 = 4.0 Hz, 1 H, 1-H),
Hb), 2.75–2.65 (m, 1 H, 2-H), 1.41 (s, 3 H, CH3), 1.33 (s, 3 H, 4.90 (dd, J5,6 = 4.3 Hz, J6,6 = 15.0 Hz, 1 H, 6-H), 4.82 (dd, J5,6
CH3) ppm. 13C NMR (62.5 MHz, CDCl3): δ = 171.9, 169.1, 156.5, 6.4 Hz, J6,6 = 15.0 Hz, 1 H, 6-H), 4.67 (d, JH,H = 11.3 Hz, 1 H,
=
136.0, 128.3, 128.1, 128.0, 127.9, 109.4, 74.5, 67.8, 66.9, 52.0, 48.6,
CH2Ph), 4.62 (d, J1,2 = 4.0 Hz, 1 H, 2-H), 4.50 (dd, J3,4 = 3.3 Hz,
J4,5 = 8.8 Hz, 1 H, 4-H), 4.49 (d, JH,H = 11.3 Hz, 1 H, CH2Ph),
4.17 (d, J3,4 = 3.3 Hz, 1 H, 3-H), 3.67 (s, 3 H, CH3O), 3.62 (ddd,
44.3, 38.1, 26.3, 24.9 ppm. MS (CI): m/z (%) = 395 (100)
[M + H]+, 91 (12) [CH Ph]+. IR (NaCl): ν = 3333, 1730, 1676,
˜
2
1531 cm–1. C19H26N2O7 (394): calcd. C 57.86, H 6.64, N 7.10; J5,6 = 4.3 Hz, J5,6 = 6.4 Hz, J4,5 = 8.8 Hz, 1 H, 5-H), 1.48 (s, 3 H,
found C 57.67, H 6.76, N 6.87.
CH3), 1.31 (s, 3 H, CH3) ppm. 13C NMR (62.5 MHz, CDCl3): δ =
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7

Job/Unit: O20103
/KAP1
Date: 02-04-12 15:01:00
Pages: 12
J. M. Otero, R. J. Estévez et al.
FULL PAPER
169.9, 136.8, 128.4, 128.0, 127.9, 112.0, 104.5, 82.0, 81.9, 77.0, 72.9,
72.2, 52.4, 41.7, 26.6, 26.1 ppm. MS (CI): m/z (%) = 382 (12) [M
+ H]+, 306 (15) [M – C2H5NO2]+, 91 (100) [PhCH2]+. IR (NaCl):
ladium on activated charcoal (10%, 0.07 g) was added to a de-
gassed solution of 11 (0.28 g, 0.74 mmol) and citric acid (0.14 g,
0.74 mmol) in MeOH (11 mL) and the mixture was stirred under
one atmosphere of hydrogen at room temp. After two days, TLC
(EtOAc/hexane, 1:1) revealed that the starting material had been
consumed. The reaction mixture was filtered through a pad of Ce-
lite and concentrated to dryness. The resulting amino intermediate
was dried under high vacuum and then dissolved in MeOH (6 mL)
and saturated aqueous NaHCO3 (3.7 mL). The mixture was cooled
to 0 °C and benzyl chloroformate (0.13 mL, 0.89 mmol) was added
dropwise. The resulting solution was stirred at room temp. for 3 h.
The reaction mixture was diluted with H2O (5 mL) and extracted
with EtOAc (3ϫ10 mL). The combined organic layers were dried
(Na2SO4), filtered and concentrated to dryness; the crude product
was purified by crystallization from Et2O to give 12 (0.21 g,
0.53 mmol, 71 % yield) as a colourless solid; m.p. 146–148 °C;
[α]2D0 = –39.8 (c = 2.13, CH3COCH3). 1H NMR (300 MHz,
CD3COCD3): δ = 7.31–7.37 (m, 5 H, 5ϫH-Ph), 5.04–5.14 (m, 2
H, CH2Ph), 4.35 (br. s, 1 H, 5-H), 4.22 (br. s, 2 H, 3-H + 4-H),
4.01 (br. s, 1 H, 6-H), 3.66 (s, 3 H, CH3O), 3.33 (d, J = 7.0 Hz, 1
H, 1-H), 3.25 (br. s, 1 H, 2-H), 2.78 (br. s, 1 H, NH), 1.66 (s, 2 H,
2ϫOH), 1.51 (s, 3 H, CH3), 1.34 (s, 3 H, CH3) ppm. 13C NMR
(75 MHz, CD3COCD3): δ = 173.7, 157.7, 139.4, 130.1, 129.4,
110.5, 80.6, 78.3, 72.3, 71.5, 67.3, 52.8, 51.8, 48.9, 29.2, 27.1 ppm.
MS (CI): m/z (%) = 396 (8) [M + H]+, 352 (9) [M – C3H7]+, 338
ν = 1741, 1557, 1376 cm–1. C H NO (381.4): calcd. C 56.69, H
˜
18 23
8
6.08, N 3.67; found C 56.39, H 6.10, N 3.73.
Methyl (1R,2R,3S,4S,5R,6R)-3-(Benzyloxy)-2,4,5-trihydroxy-6-ni-
trocyclohexanecarboxylate (10b) and Methyl (1R,2R,3S,4S,5S,6R)-
3-(Benzyloxy)-2-hydroxy-4,5-(isopropylidendioxy)-6-nitrocyclo-
hexanecarboxylate (11): A solution of compound 8 (0.89 g,
2.33 mmol) in a mixture of TFA/H2O (2:1, 35 mL) was stirred at
room temp. for 5 h. Analysis by TLC (EtOAc/hexane, 1:3) showed
that the starting material had been consumed. The solvents were
removed under vacuum and the crude product was coevaporated
with toluene (3 ϫ10 mL). The product was dissolved in MeOH
(75 mL) and 2% (w/v) aqueous NaHCO3 (25 mL) was added. The
mixture was stirred at room temp. for 12 h and acidified with cat-
ionic-exchange resin. The mixture was filtered and the solvents
were removed under vacuum to afford a chromatographically in-
separable mixture [CH2Cl2/MeOH (20:1), 0.67 g, 1.98 mmol, 85%
yield] of methyl (1R,2R,3S,4S,5S,6R)- and (1R,2R,3S,4S,5R,6R)-3-
(benzyloxy)-2,4,5-trihydroxy-6-nitrocyclohexanecarboxylate (10a
and 10b, respectively, 1:5 ratio estimated by comparison of the in-
tensity of H-6 protons in the NMR spectra; 66% de). This mixture
was stirred with 2,2-dimethoxypropane (31 mL), anhydrous CuSO4
(0.82 g, 5.14 mmol) and p-toluensulfonic acid monohydrate (0.04 g,
0.23 mmol) in acetone (23 mL) for 24 h at room temp. Saturated
aqueous Na2CO3 (2 mL) was added, the solids were filtered off and
the solvents were evaporated. The resulting residue was dissolved
in EtOAc (30 mL) and washed with saturated aqueous Na2CO3
(2ϫ15 mL). The organic layer was dried (Na2SO4), filtered and
concentrated to dryness. The crude product was submitted to silica
chromatography (EtOAc/hexane, 1:2.5 Ǟ 1:1) to afford 11 (0.55 g,
1.44 mmol, 73% yield) as a white solid, which was crystallized from
Et2O/hexane, and 10b (0.088 g, 0.26 mmol, 13 % yield) as an
amorphous white solid.
(13) [M – C H O ]+, 91 (100) [PhCH ]+. IR (KBr): ν = 3465, 3420,
˜
2
2
2
2
1749, 1737, 1691, 1529 cm–1. C19H25NO8 (395): calcd. C 57.71, H
6.37, N 3.54; found C 57.91, H 6.30, N 3.37.
(1R,2R,3S,4S,5R,6R)-2-(Benzyloxycarbonylamino)-5,6-bis(tert-
butyldimethylsilyloxy)-3,4-(isopropylidendioxy)cyclohexanecarb-
oxylic Acid (14): A solution of 12 (0.34 g, 0.85 mmol) and Ba-
(OH)2·(H2O)8 (0.80 g, 2.55 mmol) in a mixture of THF/H2O (1:2,
34 mL) was stirred at room temp. for 1 h. The mixture was neutral-
ised with acidic cationic-exchange resin, filtered and the liquids
were evaporated to dryness under vacuum. The resulting crude
product was dissolved in anhydrous DMF (3.4 mL) and the solu-
tion was heated at 80 °C for 15 h with imidazole (0.69 g,
10.2 mmol) and tert-butyldimethylsilyl chloride (1.28 g, 8.5 mmol).
MeOH (2.6 mL) was added and the solution was stirred at room
temp. for 2 h. The solvents were evaporated under vacuum and the
crude product was submitted to silica chromatography (CH2Cl2/
MeOH, 30:1) to give compound 14 (0.39 g, 0.64 mmol, 75% yield)
as a white solid, which was crystallised from CH2Cl2; m.p. 152–
154 °C; [α]2D0 = –34.0 (c = 1.33, CHCl3). 1H NMR (400 MHz,
CDCl3): δ = 7.96 (s, 1 H, CO2H), 7.25–7.20 (m, 5 H, 5ϫH-Ph),
5.04–5.01 (m, 2 H, CH2Ph), 4.39 (br. s, 1 H, NH), 4.17–3.95 (m, 4
H, 3-H + 4-H + 5-H + 6-H), 2.89 (s, 1 H, 1-H), 2.82 (s, 1 H, 2-H),
1.45 (s, 3 H, CH3), 1.26 (s, 3 H, CH3), 0.85 (s, 9 H, tBuSi), 0.80 (s,
9 H, tBuSi), 0.07 (s, 3 H, MeSi), 0.06 (s, 3 H, MeSi), 0.01 (s, 3 H,
MeSi), –0.06 (s, 3 H, MeSi) ppm. 13C NMR (125 MHz, CDCl3): δ
= 175.2, 163.0, 136.6, 128.1, 127.7, 125.5, 108.9, 78.5, 73.9, 70.1,
66.5, 49.7, 36.3, 31.4, 27.9, 25.9, 25.6, 25.6, 17.8, 17.7, –4.6, –4.9,
–5.0, –5.4, ppm. MS (CI): m/z (%) = 611 (43) [M + H]+, 610 (46)
Compound 11: Colourless solid; m.p. 126–128 °C; [α]2D0 = –86.7 (c
1
= 2.45, CHCl3). H NMR (250 MHz, CDCl3): δ = 7.43–7.32 (m, 5
H, 5ϫH-Ph), 5.04 (dd, J5,6 = 8.3 Hz, J1,6 = 12.5 Hz, 1 H, 6-H),
4.72 (d, JH,H = 11.4 Hz, 1 H, CH2Ph), 4.66 (d, JH,H = 11.4 Hz, 1
H, CH2Ph), 4.55–4.46 (m, 2 H, 2-H + 5-H), 4.38–4.34 (m, 1 H, 4-
H), 4.06 (dd, J3,4 = 2.6 Hz, J2,3 = 3.1 Hz, 1 H, 3-H), 3.74 (s, 3 H,
CH3O), 3.49 (dd, J1,2 = 2.6 Hz, J1,6 = 12.5 Hz, 1 H, 1-H), 2.85 (d,
J2,OH–2 = 7.3 Hz, 1 H, O2-H), 1.61 (s, 3 H, CH3), 1.37 (s, 3 H,
CH3) ppm. 13C NMR (62.5 MHz, CDCl3): δ = 170.2, 136.7, 128.6,
128.3, 127.8, 110.9, 84.6, 76.2, 76.0, 73.5, 72.9, 69.7, 52.7, 44.9,
27.9, 25.7 ppm. MS (CI): m/z (%) = 382 (100) [M + H]+, 91 (45)
[PhCH ]+. IR (KBr): ν = 3474, 1744, 1552 cm–1. C H NO (381):
˜
2
18 23
8
calcd. C 56.69, H 6.08, N 3.67; found C 56.43, H 6.25, N 3.70.
Compound 10b: [α]2D0 = +56.6 (c = 2.03, CH3COCH3). 1H NMR
(250 MHz, CDCl3): δ = 7.29–7.39 (m, 5 H, 5ϫH-Ph), 5.28 (dd,
J5,6 = 3.4 Hz, J1,6 = 11.9 Hz, 1 H, 6-H), 4.70 (d, JH,H = 11.6 Hz,
1 H, CH2Ph), 4.63 (d, JH,H = 11.6 Hz, 1 H, CH2Ph), 4.23–4.58 (m,
4 H, 2-H + 4-H + 5-H + OH), 3.81–3.93 (m, 3 H, 3-H + 2ϫOH),
3.76 (s, 3 H, CH3O), 3.69 (dd, J1,2 = 3.1 Hz, J1,6 = 11.9 Hz, 1 H,
1-H) ppm. 13C NMR (62.5 MHz, CDCl3): δ = 171.4, 135.7, 128.9,
128.8, 128.2, 81.0, 75.7, 73.5, 72.9, 70.5, 69.6, 52.8, 41.8 ppm. MS
(CI+): m/z (%) = 341 (6) [M]+, 282 (32) [M – C2H3O2]+, 91 (42)
[M]+, 566 (27) [M – CO ]+, 91 (100) [PhCH ]+. IR (KBr): ν = 3354,
˜
2
2
1718 cm–1. C30H51NO8Si2 (610): calcd. C 59.08, H 8.93, N 2.30;
found C 59.45, H 8.79, N 2.31.
Methyl 2-[(1R,2R,3S,4S,5R,6R)-2-(Benzyloxycarbonylamino)-5,6-
bis(tert-butyldimethylsilyloxy)-3,4-(isopropylidendioxy)cyclohexane-
carboxamido]acetate (15): A round-bottomed flask under an argon
atmosphere was charged with 14 (0.054 g, 0.090 mmol), TBTU
(0.046 g, 0.14 mmol) and anhydrous DMF (1 mL). The resulting
solution was stirred at room temp. for 5 min and HGlyOMe·HCl
(0.014 g, 0.11 mmol) was added. After 15 min, anhydrous DIPEA
[PhCH ]+, 57 (100). IR (KBr): ν = 3349, 1729, 1439 cm–1
.
˜
2
C15H19NO8 (341): calcd. C 52.78, H 5.61, N 4.10; found C 53.05,
H 5.82, N 3.83.
Methyl (1R,2R,3S,4R,5S,6R)-2-(Benzyloxycarbonylamino)-5,6-di-
hydroxy-3,4-(isopropylidendioxy)cyclohexanecarboxylate (12): Pal-
8
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20103
/KAP1
Date: 02-04-12 15:01:00
Pages: 12
Stereocontrolled Synthesis of β2-Amino Acids
(0.063 mL, 0.36 mmol) was added and the solution was stirred at
room temp. for 12 h. The solvents were removed under vacuum and
the crude product was purified by silica chromatography (EtOAc/
67.9, 52.7, 49.3, 48.4, 45.2, 42.0 ppm. MS (CI): m/z (%) = 470 (32)
[M + H]+, 452 (57) [M – OH]+, 91 (100) [PhCH ]+. IR (KBr): ν =
˜
2
3478–3416, 1714, 1659 cm–1. C20H27N3O10 (469): calcd. C 51.17, H
hexane, 1:5) to give 15 (0.050 g, 0.075 mmol, 83% yield) as a yellow 5.80, N 8.95; found C 50.85, H 6.03, N 9.12.
oil; [α]2D0 = –21.5 (c = 3.01, CHCl3). H NMR (300 MHz, CDCl3):
1
Benzyl (1R,2S,3R,4S,5R,6S)-3,4-Dihydroxy-2-(hydroxymethyl)-5,6-
δ = 7.27–7.21 (m, 5 H, 5ϫH-Ph), 6.99 (br. s, 1 H, NH), 5.09–4.84
(m, 3 H, CH2Ph + 2-H), 4.09–3.86 (m, 6 H, 3-H + 4-H + 5-H +
6-H + 2ϫH-Gly), 3.62–3.54 (m, 4 H, CH3 + H-Gly), 2.87–2.72
(m, 1 H, 1-H), 1.47 (s, 3 H, CH3), 1.27 (s, 4 H, CH3 + NH), 1.22–
1.13 (m, 1 H, NH), 0.85 (s, 9 H, tBuSi), 0.82 (s, 9 H, tBu Si), 0.05
(s, 3 H, CH3Si), 0.04 (s, 3 H, CH3Si), 0.03 (s, 3 H, CH3Si), –0.09
(s, 3 H, CH3Si) ppm. 13C NMR (75 MHz, CDCl3): δ = 171.1, 169.6,
157.5, 136.3, 128.3, 127.9, 109.4, 78.6, 77.4, 74.0, 69.7, 67.0, 52.0,
48.9, 48.7, 41.2, 28.2, 26.0, 25.7, 25.6, 17.9, 17.8, –4.3, –4.7, –4.9,
–5.5 ppm. MS (CI): m/z (%) = 682 (13) [M + H2]+, 666 (4) [M –
(isopropylidendioxy)cyclohexylcarbamate (18): A solution of β-
amino ester 12 (0.044 g, 0.111 mmol) in EtOH (1 mL) was treated
with NaBH4 (0.008 g, 0.222 mmol) at room temp. for 3 h. The mix-
ture was neutralised with acid resin, filtered and concentrated un-
der vacuum. The crude product was purified by silica chromatog-
raphy (MeOH/CHCl3, 1:16) to provide 18 (0.035 g, 0.095 mmol,
86%) as a colourless oil; [α]2D0 = +42.4 (c = 1.40, MeOH). 1H NMR
(250 MHz, CD3OD): δ = 7.28–7.18 (m, 5 H, 5ϫH-Ph), 5.00 (s, 2
H, CH2Ph), 4.19 (t, J4,5 = J5,6 = 4.2 Hz, 1 H, 5-H), 4.08 (dd, J4,5
= 4.2 Hz, J3,4 = 5.4 Hz, 1 H, 4-H), 3.94 (dd, J3,4 = 5.4 Hz, J2,3
=
CH ]+, 91 (100) [PhCH ]+. IR (KBr): ν = 3337, 1755, 1701,
˜
2
2
7.3 Hz, 1 H, 3-H), 3.74 (dd, J6,7Ј = 4.8 Hz, J7,7Ј = 11.5 Hz, 1 H, 7Ј-
H), 3.51–3.18 (m, 5 H, 2ϫOH + 1-H + 2-H + 7-H), 2.00–1.89 (m,
1 H, OH), 1.38 (s, 3 H, CH3), 1.22 (s, 3 H, CH3) ppm. 13C NMR
(62.5 MHz, CD3OD): δ = 159.0, 138.1, 129.5, 129.1, 129.0, 110.3,
80.2, 78.1, 77.9, 70.8, 67.9, 61.0, 50.1, 44.5, 28.3, 26.2, ppm. MS
(CI): m/z (%) = 368 (40) [M + H]+, 350 (38) [M – OH]+, 324 (38)
1671 cm–1. C33H56N2O9Si2 (680): calcd. C 58.20, H 8.29, N 4.11;
found C 58.49, H 8.04, N 3.97.
Methyl 2-{(1R,2R,3S,4S,5R,6R)-2-[2-(Benzyloxycarbonylamino)-
acetamido]-5,6-bis(tert-butyldimethylsilyloxy)-3,4-(isopropyliden-
dioxy)cyclohexanecarboxamido}acetate (16): According to typical
procedure III, the reaction of 15 (0.032 g, 0.047 mmol) with 10%
palladium on activated charcoal (0.003 g) in MeOH (1 mL) for 2 h,
and then with CbzGlyOH (0.011 g, 0.054 mmol), TBTU (0.030 g,
0.087 mmol) and DIPEA (0.025 mL, 0.14 mmol) in anhydrous
DMF (1 mL) for 6 h, afforded, after purification by column
chromatography (EtOAc/hexane, 1:1.5), 16 (0.025 g, 0.034 mmol,
73% yield) as a yellow oil; [α]2D0 = –16.4 (c = 1.66, CHCl3). 1H
NMR (300 MHz, CDCl3): δ = 7.37–7.31 (m, 5 H, 5ϫH-Ph), 7.02
[M – C H O]+, 260 (100). IR (CHCl ): ν = 3343, 1698, 1243, 1221,
˜
2
3
3
1053 cm–1. HRMS: calcd. for C18H26NO7 [M + H]+ 368.1631,
found 368.1706. C18H26NO7 (367): calcd. C 58.84, H 6.86, N 3.81;
found C 58.81, H 6.60, N 3.97.
(1S,2R,3S,4R,5S,6R)-4-Amino-3-(hydroxymethyl)-5,6-(isopropyl-
idendioxy)cyclohexane-1,2-diol (19): Palladium on activated char-
coal (10 %, 0.031 g) was added to a degassed solution of 18
(dd, JH,NH = 4.7 Hz, JH,NH = 7.0 Hz, 1 H, NH-Gly-OMe), 6.31 (0.031 g, 0.083 mmol) in MeOH (1 mL) and the mixture was stirred
(br. s, 1 H, NH-C-2), 5.13 (s, 2 H, CH2Ph), 4.83–4.73 (m, 1 H, 2-
H), 4.31 (dd, JH,NH = 7.0 Hz, JH,H = 17.0 Hz, 1 H, H-Gly-OMe),
under one atmosphere of hydrogen at room temp. After 3 h, TLC
(MeOH/CHCl3, 1:10) revealed that the starting starting material
4.15–4.03 (m, 4 H, 4-H + 5-H + 6-H + H-Gly-NHCbz), 3.94 (dd, had been consumed. The reaction mixture was filtered through a
J3,4 = 4.7 Hz, J2,3 = 8.8 Hz, 1 H, 3-H), 3.84 (dd, JH,NH = 5.3 Hz, pad of Celite and concentrated to dryness to afford aminoderiv-
JH,H = 17.0 Hz, 1 H, H-Gly-NHCbz), 3.65 (s, 3 H, CH3O), 3.48 ative 19 (0.019 g, 0.082 mmol, 98%) as a colourless oil; [α]2D0
(dd, JH,NH = 4.7 Hz, JH,H = 17.0 Hz, 1 H, H-Gly-OMe), 2.82–2.91 +59.9 (c = 1.38, CH3OH). 1H NMR (250 MHz, CD3OD): δ = 4.04–
=
(m, 1 H, 1-H), 1.51 (s, 3 H, CH3), 1.32 (s, 3 H, CH3), 0.92 (s, 9 H,
tBuSi), 0.90 (s, 9 H, tBuSi), 0.12 (s, 3 H, CH3Si), 0.11 (s, 3 H,
CH3Si), 0.09 (s, 3 H, CH3Si), –0.05 (s, 3 H, CH3Si) ppm. 13C NMR
4.02 (m, 2 H, 3-H + 4-H), 3.82–3.68 (m, 2 H, 1-H + 2-H), 3.56–
3.43 (m, 2 H, CH2-7), 3.34–3.31 (m, 1 H, 5-H), 3.25 (s, 1 H, OH),
3.22–3.20 (m, 1 H, 6-H), 1.84–1.75 (m, 1 H, OH), 1.38 (s, 3 H,
(75 MHz, CDCl3): δ = 171.5, 171.4, 170.5, 156.6, 136.2, 128.5, CH3), 1.24 (s, 3 H, CH3) ppm. 13C NMR (62.5 MHz, CD3OD): δ
128.1, 109.4, 78.5, 77.2, 73.9, 69.8, 67.1, 52.2, 48.9, 46.1, 45.2, 41.1, = 110.0, 80.3, 80.2, 78.0, 70.4, 61.7, 51.2, 44.5, 28.2, 26.0 ppm. MS
28.1, 26.1, 25.6, 25.5, 17.9, 17.8, –4.4, –4.8, –4.9, –5.6, ppm. MS
(CI): m/z (%) = 234 (64) [M + H]+, 176 (100). IR (NaCl): ν = 3355,
˜
(CI): m/z (%) = 739 (50) [M + H]+, 738 (100) [M]+, 737 (60) [M –
1373, 1243, 1220, 1056 cm–1. HRMS: calcd. for C10H20NO5 [M +
H]+ 234.1341, found 234.1340.
H]+, 680 (53) [M – C H O ]+, 91 (86) [PhCH ]+. IR (KBr): ν =
˜
2
2
2
2
3323, 1722, 1667 cm–1. C35H59N3O10Si2 (738): calcd. C 56.96, H
(1R,2S,3S,4S,5R,6S)-5-Amino-6-(hydroxymethyl)cyclohexane-
1,2,3,4-tetraol Hydrochloride (20): A solution of 19 (0.027 g,
0.116 mmol) in a mixture of MeOH/6 m HCl(aq) (1:1, 2 mL) was
stirred at 50 °C for 3 h. After this time, TLC (MeOH/CHCl3, 3:2)
showed that the starting material had been consumed and the sol-
vents were removed under vacuum. The crude product was dis-
solved in a small amount of MeOH, and Et2O was added dropwise
to precipitate the hydrochloride salt 20 (0.024 g, 0.106 mmol, 92%)
as an waxy white solid; [α]2D0 = +55.4 (c = 0.57, H2O). 1H NMR
(250 MHz, D2O): δ = 3.99 (br. s, 1 H, 3-H), 3.85 (dd, J6,7Ј = 5.2
8.06, N 5.69; found C 57.28, H 8.14, N 5.37.
Methyl 2-{(1R,2R,3S,4S,5S,6R)-2-[2-(Benzyloxycarbonylamino)-
acetamido]-3,4,5,6-tetrahydroxycyclohexanecarboxamido}acetate
(17): A solution of 16 (0.025 g, 0.034 mmol) in a mixture of TFA/
H2O (1:1, 4 mL) was stirred at room temp. for two days. Analysis
by TLC (ethyl acetate/hexane, 1:1) showed that the starting mate-
rial had been consumed. The solvents were removed under vacuum
and the residue was coevaporated with toluene (3ϫ10 mL) and
submitted to chromatographic purification (MeOH/CHCl3, 1:7) af-
fording 17 (0.013 g, 0.028 mmol, 82%) as a colourless oil; [α]2D0
=
Hz, J7,7Ј = 11.5 Hz, 1 H, 7Ј-H), 3.74 (dd, J6,7 = 3.1 Hz, J7,7Ј
=
1
–10.7 (c = 0.95, MeOH). H NMR (500 MHz, CD3OD, 50 °C): δ
= 7.40–7.29 (m, 5 H, 5ϫH-Ph), 5.13 (s, 2 H, CH2Ph), 4.56 (ddd,
J2,3 = 12.2 Hz, J1,2 = 11.7 Hz, J2,NH = 3.4 Hz, 1 H, 2-H), 4.09–
4.06 (m, 1 H, 6-H), 4.03 (t, J4,5 = J4,6 = 3.4 Hz, 1 H, 4-H); 3.99–
3.84 (m, 4 H, 3-H + 5-H + CH2-Gly), 3.83 (s, 3 H, CH3O), 3.77–
3.70 (m, 2 H, CH2-Gly), 2.96 (dd, J1,2 = 11.7 Hz, J1,6 = 2.0 Hz, 1
11.5 Hz, 1 H, 7-H), 3.64–3.53 (m, 4 H, 1-H + 2-H + 4-H + 5-H),
2.08 (m, 1 H, 6-H) ppm. 13C NMR (62.5 MHz, D2O): δ = 74.5,
70.4, 69.8, 68.7, 59.5, 53.9, 39.7 ppm. MS (CI): m/z (%) = 194 (100)
[M – Cl]+. IR (NaCl): ν = 3440, 1083 cm–1. HRMS: calcd. for
˜
C7H16NO5 [M – Cl]+ 194.1028, found 194.1029.
H, 1-H) ppm. 13C NMR (125 MHz, CD3OD, 50 °C): δ = 173.8, Supporting Information (see footnote on the first page of this arti-
173.7, 173.0, 159.1, 138.1, 129.5, 129.1, 129.0, 75.6, 74.2, 72.0, 71.2, cle): Glycosidase inhibition assay and X-ray diffraction structure
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Date: 02-04-12 15:01:00
Pages: 12
J. M. Otero, R. J. Estévez et al.
FULL PAPER
determination procedures, and copies of the 1H and 13C NMR
spectra for all new compounds are included.
785; b) M. I. Mangione, A. G. Suárez, R. A. Spanevello, Car-
bohydr. Res. 2005, 340, 149–153.
E. Vedejs, P. L. Fuchs, J. Org. Chem. 1971, 36, 366–367.
l-Glyceraldehyde was obtained as described, see: C.
Hubschwerlen, Synthesis 1986, 962–964.
[17]
[18]
Acknowledgments
[19]
a) Enantioselective Synthesis of β-Amino Acids (Eds.: E. Juari-
sti, V. A. Soloshonok), Wiley-Interscience, New York, 2005; b)
R. M. Ortuno, A. G. Moglioni, G. Y. Moltrasio, Curr. Org.
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Price, Tetrahedron: Asymmetry 2005, 16, 2833–2891; d) J. A.
Miller, S. T. Nguyen, Mini-Rev. Org. Chem. 2005, 2, 39–45.
a) For the first synthesis of a polyhydroxylated cyclohexane β-
amino acids, see: J. Chola, I. B. Masesane, Tetrahedron Lett.
2008, 49, 5680–5682. For the synthesis of a range of mono-,
di- and trihydroxycyclohexane β-amino acids, see: b) P. Wipf,
X. Wang, Tetrahedron Lett. 2000, 41, 8747–8751; c) I. B. Mase-
sane, P. G. Steel, Synlett 2003, 735–737; d) M. E. Bunnage, T.
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3220.
We thank the Spanish Ministry of Science and Innovation (MIC-
INN) (CTQ2009-08490) and the Xunta de Galicia for financial
support, and the former for grants to J. M. O. and F. F. N.
[1] a) A. F. Spatola, in: Chemistry and Biochemistry of Amino Ac-
ids, Peptides and Proteins, vol. 7 (Ed.: B. Weinstein), Marcel
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Date: 02-04-12 15:01:00
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Received: January 28, 2012
Published Online: ᭿
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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11

Job/Unit: O20103
/KAP1
Date: 02-04-12 15:01:00
Pages: 12
J. M. Otero, R. J. Estévez et al.
FULL PAPER
Peptidomimetics
A stereocontrolled synthesis of polyhydrox-
ylated β-amino acids is reported. The syn-
thesis of a small peptidic sequence contain-
J. M. Otero,* F. Fernández,
J. C. Estévez, R. Nash,
R. J. Estévez* .................................. 1–12
ing
a polyhydroxycyclohexanic β-amino
acid was completed. The distance between
the N- and C-termini in this new cyclic β-
amino acid is similar to those observed in
the Gly-Pro δ-turn
A Nitro Sugar-Mediated Stereocontrolled
Synthesis of β2-Amino Acids: Synthesis of
a
Polyhydroxylated
trans-2-Amino-
cyclohexanecarboxylic Acid
Keywords: Amino acids / Carbohydrates /
Michael addition / Protein engineering /
Peptidomimetics / Inhibitors
12
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Eur. J. Org. Chem. 0000, 0–0