A bioinspired look at the glucosinolate metabolic pathway. Structural insights into the reaction of benzyl isothiocyanate and d-glucosamine

Article abstract of DOI:10.1016/j.tet.2011.07.073

Through a well-established enzymatic transformation glucosinolates release reactive isothiocyanates that can undergo further metabolic pathways affording a plethora of reactive metabolites. This study explores in detail the reaction of benzyl isothiocyanate, which possesses antitumor activity as alkylating agent, with d-glucosamine, commonly employed in oral treatments against osteoarthritis and inflammation. Structures of the resulting products and their evolution have been assessed and compared with those involving d-glucose, reported previously. Chemical results suggest that clinical treatments with d-glucosamine could reduce the beneficial effects associated with diets based on glucosinolate-rich foods.

Full text of DOI:10.1016/j.tet.2011.07.073

Tetrahedron 67 (2011) 7811e7820
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A bioinspired look at the glucosinolate metabolic pathway. Structural insights into
the reaction of benzyl isothiocyanate and
D-glucosamine
,
b
b
b
b
b
Guadalupe Silvero a , Martín Avalos , Reyes Babiano , Pedro Cintas , Jose L. Jimenez , Juan C. Palacios
ꢀ
*
ꢀ
ꢀ
a
ꢀ
ꢀ
ꢀ
Departamento de Química Organica e Inorganica, QUOREX Research Group, UEX, Facultad de Veterinaria, E-10003 Caceres, Spain
b
ꢀ
ꢀ
Departamento de Química Organica e Inorganica, QUOREX Research Group, UEX, Facultad de Ciencias, E-06006 Badajoz, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Through a well-established enzymatic transformation glucosinolates release reactive isothiocyanates
that can undergo further metabolic pathways affording a plethora of reactive metabolites. This study
explores in detail the reaction of benzyl isothiocyanate, which possesses antitumor activity as alkylating
Received 29 March 2011
Received in revised form 20 July 2011
Accepted 24 July 2011
agent, with
flammation. Structures of the resulting products and their evolution have been assessed and compared
with those involving -glucose, reported previously. Chemical results suggest that clinical treatments
with
foods.
D-glucosamine, commonly employed in oral treatments against osteoarthritis and in-
Available online 29 July 2011
D
Keywords:
Benzyl isothiocyanate
D-glucosamine could reduce the beneficial effects associated with diets based on glucosinolate-rich
D
-Glucosamine
Ó 2011 Elsevier Ltd. All rights reserved.
Glucosinolates
Imidazolidin-2-thione
1. Introduction and background
and water. The degradation pathway induced by myrosinase is also
influenced by factors, such as pH and the presence of metal ions.2
Glucosinolates are a family of glycosides, which are enzymati-
cally hydrolyzed in damaged plant tissues giving rise to potentially
toxic metabolites. They are present in seeds of Cruciferae and
Brassicaceae plants. Hydrolysis of the glucoside bond via the en-
zyme myrosinase, a thioglucosidase, results in a thiohydroximate
sulfonate. This compound usually yields an isothiocyanate by
Epidemiological studies show that consumption of Brassica
vegetables is associated with a reduced incidence of cancers at
a number of sites including the lung, stomach, colon, and rectum.3
The processes of ingestion and digestion of Brassica vegetables lead
to glucosinolate hydrolysis. The liberated ITCs have shown to be
potent and selective inhibitors of carcinogenesis induced by a va-
riety of chemical carcinogens,4 such as tobacco-derived nitrosa-
mines and polycyclic aromatic hydrocarbons and appear to act at
a number of stages during the tumor development process.5 ITCs
act as blocking agents by modifying the metabolism of carcinogenic
compounds through their influence on biotransformation enzymes.
The action of isothiocyanates is generally believed to enhance the
activity of phase II enzymes,6 with some evidence that they also
€
a Lossen-type rearrangement prompted by the sulfate leaving
group.1
The isothiocyanates (ITCs) are therefore an important group of
breakdown products derived from glucosinolates (Scheme 1) and
constitute powerful electrophiles capable of reacting, under phys-
iological conditions, with a wide range of nucleophilic species, such
as amino acids and peptides, and other biogenic amines, alcohols,
CH2OH
D-glucose
H2O
O
HO
HO
-S
R
S
R
-
R-N=C=S + HSO4
N
myrosinase
OH
-
N
OSO3
-
OSO3
Glucosinolate
Scheme 1.
* Corresponding author. E-mail address: gsilvero@unex.es (G. Silvero).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.07.073

7812
G. Silvero et al. / Tetrahedron 67 (2011) 7811e7820
inhibit phase I enzymes.7 This dual action is thought to reduce the
production of electrophilic intermediates with carcinogenic activity
and to enhance the detoxification and clearance of carcinogens.
ITCs also serve as suppressing agents during the promotion phase
of the neoplastic process. Recent work has shown that ITCs act on
signal transduction pathways within the cell, both inducing apo-
ptosis and inhibiting cell growth.8,9 In vivo, ITCs are conjugated
with glutathione and then sequentially metabolized to mercapturic
acids.10
One of the most intensively studied ITCs with regard to cancer
chemoprevention and genotoxic effects is benzyl isothiocyanate
(BITC), a product of enzymatic hydrolysis of glucotropaeolin.11ꢀ13
BITC and its m-methoxy derivative appear to be the most abun-
dant degradation products resulting from glucosinolates present in
certain plants, such as Peruvian maca (Lepidium meyenii).13
temperature this reaction proceeds slowly and BITC is poorly sol-
uble; only one new product having Rf 0.47 (CH2Cl2eMeOH, 4:1 v/v)
could be detected. In order to speed up the transformation, both
reactants were heated at 75 ꢁC in a hydroalcoholic solution for 2 h
(Scheme 2). The process took place smoothly and TLC monitoring
revealed the formation of three major products (with 99% overall
yield). One of them could easily be isolated on cooling and identi-
fied as N,N0-dibenzylthiourea (2, 37%).19 Further inspection of the
mother liquors showed the presence of two additional substances
(Rf values: 0.47 and 0.62), which could be isolated by flash chro-
matography. Their elemental analyses and spectroscopic data are
consistent with structures of (4R,5S)-1-benzyl-5-hydroxy-4-(
D-
arabino-tetritol-1-yl)-1,3-imidazolidin-2-thione (3, 27%) and 1-
benzyl-(1,2-dideoxy-
a
-D
-glucofurano)[2,1-d]imidazolidin-2-thione
(4, 35%), respectively.
Bn
S
N
H OH
OH
HOH2C
CH2OH
N
S
HO
H
O
HO
O
H
i
Bn
Bn
Bn
HO
N
H
N
H
HO
N
+
+
OH
OH
HCl.H2N
OH
HN
S
2
1
4
CH2OH
3
Scheme 2. i, NaHCO3, PhCH2NCS,
D.
In a recent investigation, Kruse et al. have identified the main
products resulting from the reaction of BITC with
-glucose.14 Such
substances were heterocycles derived from 1,3-oxazolidin-2-
thiones and 1,3-thiazolidin-2-thione. Although mechanistic
study was lacking, the authors were unable to detect the presence
of simple addition products like thiourethanes. Given our past ex-
perience on amino sugars and sugar isothiocyanates, the above
research prompted us to evaluate the corresponding reaction of
The structure attributed to 3 agrees with a molecular peak (m/z
328) determined by mass spectrometry. The existence of water in
the crystal lattice is also evidenced by a weak and broad IR ab-
D
a
sorption at w1638 cm .
ꢀ1 20 NMR spectra of 3 are similar to those of
analogous derivatives.21,22 The 1H NMR spectrum shows signals for
the NH and OH groups at the heterocyclic ring at 8.00 and
6.65 ppm, respectively, while 13C NMR resonances for the thio-
carbonyl group and C-5 appear at 181.0 and 83.7 ppm, respectively
(Figs. S1eS3). The latter rules out an alternative isomeric structure
BITC with D-glucosamine, which could be an appropriate in vitro
model on the interaction of secondary plant metabolites and nu-
trients or bioactive substances.
of 2-benzylthioureido-2-deoxy-
anomeric carbon would resonate at w90 ppm (
w95 ppm (in the case of the
anomer).21,23,24 The proton linked to
C-5 ( 5.31 ppm) exhibits a small coupling constant with the H-4
D
-glucopiranose, for which the
a
anomer) or
D-Glucosamine is a key precursor of peptidoglycan structures
b
and plays therefore an important role in the production of collag-
d
enous fibers present in connective tissue, such as cartilages and
proton (J4,5¼3.2 Hz), thereby pointing to a trans relationship be-
tween such protons and, as a result the configuration at C-5 should
be R.21e23 The carbon atoms located along the polyhydroxyl side
chain show chemical shifts similar to those found in acyclic frag-
ments of sugar derivatives.24
Compound 3 equilibrated in solution with another substance
exhibiting close NMR patterns and chemical shifts (Scheme 3). The
latter was identified as the cis epimer (5), although the former was
synovial fluid.15
D-Glucosamine is orally administered against bone
degenerative diseases, especially osteoarthritis.16 It also exhibits
anti-inflammatory properties by inhibiting proteolytic enzymes;
and in this context
represents a valuable surrogate of conventional agents like ibu-
profen in reducing pain.17 About 90% of
-glucosamine sulfate ad-
D-glucosamine in the form of food supplements
D
ministered orally can be absorbed by the large intestine and crosses
easily other biological barriers. Pharmacokinetic studies show
variable levels of this and other amino sugars in serum after ad-
ministration of chondroitin sulfate or glucosamine.18
Since both ITCs and D-glucosamine can be present in biological
fluids, the present study explores structural and mechanistic details
on their interaction under physiological-like conditions. Our study
sheds also light into putative metabolic pathways and the product
distribution is compared with that found previously with
D-
glucose.14
2. Results and discussion
The condensation of 2-amino-2-deoxy-D-glucopyranose (1)
Scheme 3.
with BITC has been explored in an aqueous environment. At room

G. Silvero et al. / Tetrahedron 67 (2011) 7811e7820
7813
prevalent in the equilibrium (3: w82%). The relative cis disposition
between H-4 and H-5 in 5 could be inferred from the large coupling
heating a solution of 3 in 30% aqueous acetic acid the same mixture
of 4 and 6 was obtained in 67% overall yield (Scheme 4).
Bn
S
Bn
S
N
N
H
OH
OH
N
N
H
HO
H
O
H
i
Bn
HOH2C
+
HO
N
HO
OH
OH
OH
OH
HN
S
4
CH2OH
CH2OH
6
3
iv
OH
CH2NHBn
OH
OH
OH
O
HOH2C
HO
HO
HOH2C
HO
HO
O
O
ii
iii
OH
NHBn
(CO2H)2
OH
OH
7
8
9
Scheme 4. i, AcOH 30%,
D; ii, BnNH2, EtOH, D; iii, (CO2H)2, D; iv, KSCN, D.
constant (J4,5¼7.6 Hz).21e23 Similar epimerizations have been pre-
viously observed.22a,25
The structure of 6 could also be established by analytical and
spectroscopic methods. The IR sharp absorption at w1633 cmꢀ1
is consistent with the endocyclic double bond. The heterocyclic
In both stereoisomers the benzyl protons appear as an AB sys-
tem, thus pointing to their diastereotopic nature and resonating at
very different chemical shifts (Dd w0.75 ppm, Jgem¼16.0 Hz for 3;
Dd w1.07 ppm, Jgem¼15.4 Hz for 5). This strong anisotropy is not
only due to the presence of a vicinal C]S group, but also to con-
formational restriction of the benzyl group.26
moiety exhibits characteristic NMR signals for the NH
11.92 ppm) and H-5 ( 6.84 ppm) protons, which are strongly
deshielded, whereas the thiocarbonyl group ( 161.73 ppm) is
shifted upfield relative to that of compound 3. Furthermore, the
(d
d
d
chemical shifts for C-4 (d 132.07 ppm) and C-5 (d 115.91 ppm)
On the other hand, the mass spectrum of 4 shows a molecular
peak at m/z 310. IR absorptions characteristic of the aromatic ring
and OH groups are likewise consistent with its structure. Again, the
presence of water in the crystal lattice is evidenced by a weak and
broad absorption at w1630 cmꢀ1, overlapping the thioamide NH
are characteristic of olefinic carbons.21,22 It is worth mentioning
that the previously observed separation in the benzyl protons
has essentially vanished and the former AB system almost col-
lapses into a singlet (Dd w0.05 ppm, Jgem¼14.8 Hz). This re-
duction in anisotropy should be ascribed to
a greater
band at w1556 cm
.
ꢀ1 20 The signals of the NH and the heterocyclic
conformational freedom because there is no substituent at C-5
(Figs. S7 and S8).
H-1 protons resonate at 8.90 and 5.59 ppm, whereas the thio-
carbonyl and C-1 carbons appear at 182.8 and 92.8 ppm, re-
spectively, and are close to those found in analogous bicyclic
systems.21e23b,27 A null coupling between H-2 and H-3 (J2,3¼0 Hz)
along with the downfield chemical shift of C-4 (80.3 ppm), more
deshielded than C-5 (68.7 ppm), suggest a furanoid structure for
the sugar ring, while the large coupling constant J1,2 (w6.6 Hz) is
also characteristic of a cis fusion between the heterocyclic moiety
and furanose rings (Figs. S4eS6).21ꢀ23,27,28
The fragmentation pattern observed in the mass spectrum of 4
also agree with the proposed structure for this substance (Scheme
S1). Together with the above-mentioned molecular peak (m/z 310),
characteristic peaks evidence the loss of one or two water mole-
cules (m/z 292 and 274). Likewise, the peak at m/z 190 corresponds
to the heterocyclic fragment, while the base peak can be attributed
to a benzyl-tropilium ion (m/z 91).29a The mass spectrum of 3
shows its molecular peak (m/z 328) with low intensity, whilst the
remaining signals are almost coincidental with those of 4, which
reveals that 3 losses one water molecule to give 4 and the latter
undergoes the subsequent fragmentations.
The low-resolution mass spectrum of 6 reveals a molecular peak
at m/z 310 and [MþNa]þ at m/z 333. Intense peaks can also be at-
tributed to [MþH]þ at m/z 311, and successive water elimination.
An important fragmentation corresponds to loss of the phenyl
group resulting in ions with m/z 233 (100%) and m/z 234 (Scheme
S2).
Moreover, the imidazoline derivative 6 could be prepared by an
alternative route as depicted in Scheme 4. Thus, -mannose (7) was
D
first converted into N-benzylfructosamine oxalate 9,30 through the
intermediacy of N-benzylmannosylamine 8, which was further
treated with potassium thiocyanate.31 The resulting product had
the same physical and spectroscopic properties as the compound
obtained in dehydratation reaction of 3.
To further confirm the above structures, their acetylated de-
rivatives were generated by conventional treatment with acetic
anhydride and pyridine at ꢀ20 ꢁC. The acetylation of 3 led to a re-
action mixture, whose NMR analysis identified the presence of 10
and 11, which could not be purified due to their facile de-
composition. On the contrary, the acetylation of 4 afforded com-
pound 12 in good yield. The latter showed its molecular peak at m/z
436, with intense fragmentations corresponding to ions [MþH]þ
(100%), [M]þ, and tropilium. Other diagnostic fragmentations de-
rived from successive elimination of three molecules of acetic acid,
as well as of acetic anhydride and acetyl, which are characteristic of
polyacetylated sugars (Scheme S3).29b
According to previous studies, the acid treatment of 3 would
afford compound 4 by cyclization and water elimination.21,22b,27
Thus, the condensation of 1 with BITC, adding acetic acid to the
reaction mixture, resulted in formation of 4 plus the isomeric
imidazoline-2-thione 6. This process was rather sluggish and both
substances could be isolated in low yields. In stark contrast, on

7814
Bn
G. Silvero et al. / Tetrahedron 67 (2011) 7811e7820
S
Bn
S
Bn
S
The reaction of monosaccharides and their amino derivatives
(14) with heterocumulenes (15) has long been known and the
mechanistic pathway is now well established (Scheme 6).21e23
Such transformations occur at pH>7 via the addition of a hy-
droxyl (14, Y¼O) or amino (14, Y¼NR) group to the hetero-
cumulenic system, followed by intramolecular cyclization of
a transient intermediate (16) to give a heterocyclic derivative (17).
N
N
N
H
OAc
N
N
H
OAc
N
AcO
H
Ac
O
H
AcOH2C
Bn
N
AcO
AcO
AcO
OAc
OAc
CH2OAc
OAc
OAc
CH2OAc
HN
OAc
OAc
CH2OAc
S
12
10
11
13
The absence of acetylation at the nitrogen atom of 12 under such
mild acetylating conditions is evidenced by the IR absorption (NH
stretching) at 3383 cmꢀ1 and a proton signal at 6.50 ppm. In ad-
dition, there are only three signals for acetyl groups, and coupling
0
constant values for J4,5 (6.4 Hz) and J4,1 (0.0 Hz) are again consistent
Scheme 6. The reaction of sugar and amino sugars with heterocumulenes.
with both a furanoid structure for the sugar moiety and cis fusion
between the two heterocycles (Figs. S9 and S10).
Exhaustive studies have been conducted on 2-amino-2-
deoxyaldoses (14, Y¼NH or NR). In some circumstances, the in-
termediate 16 is stable enough and can be isolated, such as ureas
(16, Y¼NH, X¼O, Z¼NAr) arising from reaction of 2-amino-2-
deoxyaldoses with aryl isocyanates.23 The corresponding thio-
ureas, however, are much more reactive and the final product 17
(Y¼NH, X¼S, Z¼NAr) is generally the first isolable substance.21
At pH<7 the monocyclic structures 17 can be converted into
bicyclic ones (18) or unsaturated heterocycles (19). Both processes
are indeed competitive and can be rationalized as depicted in
Scheme 7; either a displacement reaction (path a) leading to an
intramolecular cyclization, or an elimination reaction (path b)
giving rise to an unsaturated derivative.21e23
The acetylation of 6 gave rise to a mixture of 11 and 13 in var-
iable ratios depending on the experimental conditions. Thus,
acetylation at ꢀ20 ꢁC resulted in the preferential formation of 11;
while compound 13 was instead prevalent at 80 ꢁC. The mono-
thioimide structure present in 13 enables a facile elimination of the
N-acetyl group by solvolysis and, after crystallization from ethanol,
11 could be obtained as an analytically pure sample.
The low-resolution mass spectrum of 11 gave a molecular peak
at m/z 478 (Scheme S4). The presence of the imidazolin-2-thione
ring manifests itself by proton shifts of the NH and endocyclic ]
CH fragments at 11.22 ppm and 6.58 ppm, respectively, as well as
the resonances of olefinic carbons: C-4 (124.1 ppm) and C-5
(116.3 ppm). In addition, four signals attributed to acetyl groups
corroborate the identity of 11 still further (Figs. S11eS13).
Compound 13 shows, in its 1H NMR spectrum, five signals for
the acetyl groups. Three of them resonate at w2.1 ppm, which can
be attributed to acetates, while two signals are shifted downfield (
d
3.14 ppm) and upfield ( 1.66 ppm), respectively. The former does
d
correspond to the acetyl group on the heterocyclic nitrogen; its
unusual shift results from a preferential E conformation adopted by
the acetamido group. This is the most stable conformation that
minimizes the dipole effects caused by the carbonyl and thio-
carbonyl groups (Scheme 5). In such a conformation the methyl
group lies in the deshielding zone of the C]S bond.21,27
Scheme 7.
It is worth pointing out that the corresponding reaction involving
amino sugars and carbon disulfide only produces the monocyclic
structure (17, Y¼NH, X¼Z¼S) without any trend to follow the above-
mentioned transformations.32,33 In contrast, similar structures to
those obtained in the reactions of amino sugars with iso(thio)cya-
nates, i.e., 18 and/or 19, have also been reported with potassium
cyanate,34,35 potassium thiocyanate,36 and cyanamide.37
Given previous premises, the fate of the condensation of D-glu-
cosamine (1) and BITC is collected in Scheme 8, which accounts for
a rationale capable of explaining the product distribution observed.
The process yields initially a thioureido derivative 20, which via an
aldehyde intermediate (21), cyclizes to the imidazolidin-2-thione 3.
Finally, under acid catalysis, the latter converts into a furanoid
structure (4) or undergoes dehydration to yield 6. Furthermore, the
acid treatment of 4 may also cause its transformation into 6.38
Scheme 5. Dipole effects in E and Z conformations of the acetamido group in 13.
The N-acetyl group in compound 13 causes significant proton
shift variations with respect to those found in 11. While H-4 un-
dergoes a slight shielding relative to its homologous signal in 11 (Dd
w0.1 ppm), H-10 is strongly deshielded (Dd w0.5 ppm). Moreover,
the acetyl group at C-10 lies in the shielding zone of the olefinic
bond, thus undergoing
a rather unusual chemical shift (d
w1.66 ppm) for an acetyl group of a polyhydroxylated chain
(w2.1 ppm) (Figs. S14 and S15).
Scheme 8. i, BnNCS, pH>7; ii, AcOH 30%,
D; iii, CF3COOH, D.

G. Silvero et al. / Tetrahedron 67 (2011) 7811e7820
7815
This mechanism equally accounts for the regioselectivity and
stereochemistry observed during the cyclization pathway, i.e.,
formation of a cis-fused furanoid bicycle (4). The Baldwin rules
suggest that a 5-exo-tet cyclization (18) should be entropically
favored over a 6-exo-tet ring closure leading to a cis-fused het-
erocycle,39 which is in turn both the thermodynamic and kinetic
product. Formation of alternative cis-fused bicycles having a pyr-
anoid subunit, such as 22 or trans-fused structures like 23 and 24
have not yet been detected. The willingness to reach the most
stable furanoid structure can even be observed under solvent-free
ionizing conditions, such as in mass spectra recording. It should be
mentioned, however, that analogous compounds of 22 and 24
have been synthesized.21,40 In any case, cis-fused analogs of 23
have not been reported, due presumably to the greater steric
tension associated with such a structure.
coupling J1,2 is however high because the H-1 and H-2 protons are
eclipsed (dihedral angle w0ꢁ).46 In addition, this conformation is
also characterized by a W arrangement between H-2 and H-4,
which translates into
a significant long-range coupling J2,4
(w0.8e1.3 Hz).21
Accordingly, the couplings described for compounds 28 (or 31)
are actually consistent with the alternative structure 32. The pyr-
anoid structure for 28 (or 31) was suggested on the basis of its
mass-fragmentation pattern: the loss of 61 units from [MþNa]þ to
afford the peak of m/z 273.14 Nevertheless, this fragmentation is
also typical of furanoid structures, such as 32 and proceeds analo-
gously to that of 4, which is broken down to m/z 249.
Likewise, structures possessing D-manno configuration, both b-
furanose (39) and b-pyranose (40), should be ruled out. As held
previously,14 these structures would have been formed if, prior to
CH2OH
CH2OH
H
OH
OH
Bn
O
O
HO
HO
HO
HO
N
Bn
O
N
HOH2C
Bn
N
S
HN
HN
HN
S
23
24
22
S
Although the reaction of monosaccharides or their 2-amino
derivatives with heterocumulenes follows well-established
reaction with BITC, D-glucose had undergone the so-called Lobry de
a
BruyneAlberda van Ekenstein isomerization,47,48 via successive
mechanism, some erroneous structures have appeared in the lit-
erature on describing related processes. Thus, it has been reported
enolizations under the experimental basic conditions. Such isom-
erizations have in fact been reported in the reaction of
amine with aryl isocyanates at pH>10, to give 5-hydroxyimi-
dazolidin-2-ones derived from
-mannosamine.23a
D-glucos-
that the acid-catalyzed condensation of D-glucose and urea pro-
duces the bicyclic pyranose 25;41 although a further revision by the
D
authors unveiled the most plausible structure 26.42
Once again, the coupling pattern to be expected for such sub-
stances would be markedly different to those measured experi-
mentally for 32. Thus, the J2,3 values shown by 43 and 44 with D-
manno configuration, which are the acetylated derivatives of 41 and
42, respectively, and imidazolidin-2-ones 45 and 4623a are much
larger than zero (Table 1).49
In their recent study Kruse et al. reported that structures 27e30
should be associated to the four major products generated in the
reaction of
D
-glucose and BITC (Scheme 9).14 It is obvious that 27
represents the oxo-analogous derivative of 3, from which a cis-
configured bicyclic structure, such as 32, and not the trans-config-
ured one 28, would result.
Scheme 9. i, BnNCS, NaOH, pH w11,
D
(95 ꢁC).
The different bicyclic structures possessing
D
-gluco configura-
Table 1
tion can easily be assessed through an analysis of their coupling
constants, which depend on the dihedral angle between vicinal
protons. Table 1 shows these diagnostic values for compounds 4,
25,40 26,43 32,14 33,44 34,27 35,45 and 36.21
A cis-fused furanoid structure present in compounds 4, 26,
32e34 manifests itself by a null or negligible J2,3 coupling along
with a medium-high value of J1,2. Such couplings reflect directly the
geometry adopted by such protons: an angle of w25ꢁ between H-1
and H-2 placed in a relative cis disposition (37) and an angle of
w90ꢁ between H-2 and H-3 arranged in trans (38).
Coupling constants (Hz) for representative model compoundsa
0
0
J6,6
Compound
Structure
J1,2
J2,3
0.6
J3,4
J4,5
J5,6
J5,6
26
32b
33
34
4
35
25
36c
43
44
45
46
a
-Furanose
5.4
5.6
5.5
6.3
6.4
8.8
6.5
7.9
6.2
3.7
7.3
7.3
2.4
2.6
2.8
1.8
2.8
7.7
4.7
3.1
4.0
d
9.0
7.7
9.1
8.6
9.2
9.7
d
2.5
3.5
2.4
2.3
2.4
2.1
2.2
6.2
2.5
3.0
2.2
2.5
5.6
5.6
5.2
5.4
5.6
5.5
3.4
3.0
5.0
5.0
4.9
4.9
12.2
11.5
12.3
11.0
12.2
12.4
12.4
d
0.0
<0.5
0.0
0.0
b
a
-Pyranose
-Pyranose
10.8
4.7
3.1
5.7
3.5
6.5
9.1
9.0
6.0
d
b
b
b
b
-Furanose
-Pyranose
-Furanose
-Furanose
12.1
12.3
11.1
12.3
For pyranoid structures involving a trans fusion, like in 35, the D-
glucopyranose preserves its 4C1 conformation, and hence all cou-
plings show high values consistent with an antiperiplanar re-
lationship for H-1, H-2, H-3, H-4, and H-5. In stark contrast, a cis
fusion in the bicyclic framework, like in 25 and 36, forces to a 0S2
conformation, which results in moderate values for J2,3 and J3,4. The
3.7
4.2
6.5
8.9
a
For comparative purposes, the numbering of the parent D-glucose has been
maintained.
b
c
Described as 28 or 31.14
J2,4¼0.8 Hz.

7816
G. Silvero et al. / Tetrahedron 67 (2011) 7811e7820
OAc
H
CH2OH
H
OH
OH
CH2OH
CH2OAc
O
OAc
O
O
HO
HO
HO
HO
O
AcO
AcO
O
H
R
AcOH2C
R
HOH2C
N
N
N
R
Ph
N
N
O
Y
O
HN
O
O
X
X
X
25
X=O, R=H
S
33 Y=X=O, R=Ph
26 X=O, R=H
36
35
31 X=S, R=Bn
34
32
Y=NH, X=S, R=Ph
Y=NH, X=S, R=Bn
X=S, R=Bn
4
~25º
H2
HO
R
~90º
H1H2
J
1,2 > 5 Hz
J
< 1 Hz
2,3
H1
HOH2CHOHC
H3
R
HO
N
Y
Y
N
X
O
H3
O
X
HOH2CHOHC
38
37
X
Ph
N
N
R
N
O
O
O
H
OZ
OZ
H
OZ
OZ
ZOCH2
O
H
X
ZO
N
O
O
R
ZOCH2
ZOCH2
ZO
45 Z=H
40 X=S, Z=H, R=Bn
39 X=S, Z=H, R=Bn
46
Z=Ac
42
X=O, Z=H, R=Ph
41
X=O, Z=H, R=Ph
44
X=O, Z=Ac, R=Ph
43
X=O, Z=Ac, R=Ph
The above considerations clearly indicate that the chiral carbons
The absolute stereochemistry of 29 has not yet been de-
in 32, and hence in 27, possess the same configuration as the
termined, this substance being reported as 3-benzyl-4-
starting
D-glucose. This fact equally suggests that it is unnecessary
hydroxy-4-hydroxymethyl-5-(D-erythro-1,2,3-trihydroxypropyl)-
to invoke a previous isomerization of
D
-glucose into -fructose to
D
1,3-oxazolidin-2-thione (surprisingly depicted as the threo iso-
mer). It seems plausible to anticipate the erythro configuration
for such a substance (52) because C-3, C-4, and C-5 carbon atoms
explain the experimental results. This behavior is also reminiscent
of data reported several decades ago by the teams of Hodge44 and
Kenne49 for 2-O-phenylcarbamoyl-
D-glucopyranose (49), gener-
possess the same configuration as the parent
absolute stereochemistry of 30 ( -manno configured) however
could be determined by X-ray diffraction.14 Scheme 11 should
D-glucose. The
ated by hydrolysis of 47 or 49, which cyclizes under basic condi-
tions to 50. The latter can further be converted into a furanoid
bicycle (51, Scheme 10), in following a similar trend to the reaction
D
therefore reflect the actual situation found in the reaction of D-
of
D-glucosamine with BITC (Scheme 8).
glucose with BITC.
Scheme 10. i, HCl 0.1 M; ii, H2SO4 1 M; iii, pH>7; iv, pH<7.
Scheme 11. i, BnNCS, NaOH, pH w11,
D
(95 ꢁC).

G. Silvero et al. / Tetrahedron 67 (2011) 7811e7820
7817
The formation of the 1,3-thiazolidin-2-thione derivative (30),
Consumption of
D
-glucosamine and glucosinolate-rich vegeta-
according to Kruse and associates, was probably initiated by the
reaction of benzylamine and hydrogen sulfide (liberated from the
hydrolysis of BITC) with D-glucose giving transitional 2-sulfanyl-N-
bles may thus destroy the isothiocyanates resulting from glucosi-
nolate hydrolysis, thereby reducing the beneficial effects attributed
to such heterocumulenes.
benzyl glucosylamine and, subsequently, a further amount of BITC
was added to the thiol group formed and the reaction was com-
pleted intramolecularly.14 However, this rationale does not account
4. Experimental
for the configurational inversion at C-2 that converts the
configuration into -manno.
It is obvious that formation of 52 takes place after isomerization
-glucose into
-fructose.47,48 The generation of compounds 27,
30, 32, and 52 can easily be rationalized by invoking the same
benzylthiocarbamate intermediate (i.e., 53 or 57), which may either
cyclize into 27 or 52, respectively, or undergo a SN2 reaction that
D-gluco
4.1. General methods
D
Melting points were determined on Gallenkamp and Electro-
thermal apparatus and are uncorrected. Optical rotations were
measured at 22ꢂ5 ꢁC on a PerkineElmer 241 polarimeter. IR
spectra were recorded in the range 4000e600 cmꢀ1 on FT-IR
THERMO spectrophotometer. Solid samples were recorded on KBr
(Merck) pellets. 1H and 13C NMR spectra were recorded on a Bruker
500 or with a Bruker 400 AC/PC instrument at 400 and 100 MHz,
respectively, or with a Bruker AC 200-E instrument at 200 and
50.3 MHz, respectively, in different solvent systems. Assignments
were confirmed by homo- and hetero-nuclear double-resonance
of
D
D
produces most likely 2-deoxy-2-sulfanyl- -mannose (54), which
D
further reacts with BITC giving rise to a benzyldithiocarbamate
(55). Cyclization of the latter to yield 30 should largely be favored
and proceed via a transient imine generated by reaction with
benzylamine (Scheme 12).
Scheme 12. i, BnNCS, NaOH, pH w11,
D
(95 ꢁC); ii, pH>7; iii, pH<7; iv, SHꢀ; v, OHꢀ; vi, BnNH2.
3. Conclusions
and DEPT or HMQC. TMS was used as the internal reference
(
d
¼0.00 ppm) for CDCl3 solutions only and all J values are given in
The results reported in this paper provide a complete dissection
on the reaction of BITC (a product of enzymatic hydrolysis of glu-
cotropaeolin and inhibitor of carcinogenesis) with D-glucosamine (a
hertz. Microanalyses were determined on a LECO 932 analyser at
the Universidad de Extremadura (Spain). High resolution mass
spectra (chemical ionization) were recorded on an Autospec-Q
spectrometer by the Servicio de Espectrometría de Masas de la
Universidad de Sevilla (Spain).
common anti-inflammatory agent), and represents a plausible
in vitro mimicry of this transformation under physiological condi-
tions. All products have been thoroughly characterized and their
formation can be explained through a mechanism that involves an
initial thiourea as key step, which undergoes subsequent cycliza-
tion. This mechanistic proposal accounts for all the experimental
facts and casts doubt on previous conjectures.
These results prove that ITCs, which may act as selective in-
hibitors of carcinogenesis, generated from other glucosinolates,
such as 4-hydroxybenzyl isothiocyanate (58, from sinalbin50), allyl
isothiocyanate (59, from sinigrin51), sulforaphane or 4-(R)-meth-
ylsulfinylbutyl isothiocyanate (60, from glucoraphanin6b,52) or 2-
phenylethyl isothiocyanate (61, from gluconasturtiin53), among
others, would indeed give rise to similar metabolites to those of
4.1.1. (4R,5R)-1-Benzyl-5-hydroxy-4-(
zolidin-2-thione (3) and 1-benzyl-(1,2-dideoxy-
d]imidazolidin-2-thione (4). To a solution of 2-amino-2-deoxy-
D
-arabino-tetritol-1-yl)imida-
a-D
-glucofurano)[2,1-
a-D-
glucopyranose hydrochloride (1) (3.61 g, 16.8 mmol) in water
(20 mL) were added NaHCO3 (1.54 g, 18.5 mmol) and benzyl iso-
thiocyanate (2.2 mL, 16.8 mmol) under stirring. The mixture was
diluted with ethanol (30 mL) to obtain a homogenous solution that
was then heated at 75 ꢁC (external bath) for 2 h. When the mixture
was left to room temperature N,N0-dibenzylthiourea (2) crystallized
spontaneously as a white solid (0.80 g, 37%). Subsequent column
chromatography of mother liquors (CH2Cl2eMeOH, 3:1) afforded 3
(1.48 g, 27%) and 4 (1.82 g, 35%).
BITC by reaction with
D-glucosamine.
NCS
NCS
NCS
NCS
59
HO
S
O
58
60
61

7818
G. Silvero et al. / Tetrahedron 67 (2011) 7811e7820
Compound 3 have Rf 0.47 (CH2Cl2eMeOH 4:1), mp 83e84 ꢁC
(decomp.); [
þ8.0 (c 0.5, pyridine); vmax 3500e3000 (OH, NH),
1638 (H2O crystallization),20 1077 (CeO), 1490, and 780 cmꢀ1 (ar-
omatics); 1H NMR (400 MHz, DMSO-d6)
8.03 (s, 1H, NH),
Method b. To a solution of 1 (2.89 g, 13.4 mmol) in water (17 mL)
were added NaHCO3 (1.23 g, 14.6 mmol) and benzyl isothiocyanate
(1.78 mL, 13.4 mmol) under stirring. The mixture was diluted with
ethanol (70 mL) to obtain a homogenous solution that was then
heated at 80 ꢁC (external bath) for 2 h. When the mixture was left to
room temperature spontaneously crystallized 2 as a white solid
(0.087 g, 2.7%). Mother liquors were evaporated to dryness and the
residue obtained was treated with 30% aqueous acetic acid (118 mL)
and heated at w100 ꢁC (external bath) for 30 min. The mixture was
then washed with chloroform (3ꢃ25 mL) and the aqueous phase
was collected and evaporated to dryness. The residue was crystal-
lized with ethanol and a solid mixture of 4 and 6 was afforded.
Recrystallization with 96% ethanol yielded compound 6 (0.27 g,
6.4%). Preparative TLC of mother liquors (chloroformemethanol,
7:1) afforded compound 4 (0.32 g, 7.6%).
a
]
D
d
7.36e7.24 (m, 5H, Ar), 6.65 (d, J5,OH¼8.0 Hz, 1H, C5eOH), 5.15 (d,
J¼15.6, 1H, CH2ePh), 4.93 (dd, J4,5¼3.2, J5,OH¼7.6 Hz, 1H, H-5), 4.68
(d, J1 ,OH¼6.4 Hz, 1H, C10eOH), 4.54 (d, J2 ,OH¼8.0 Hz, 1H, C20eOH),
0
0
4.52 (d, J3 ,OH¼7.6 Hz, 1H, C30eOH), 4.40 (t, J4 ,OH¼J4 ,OH¼5.6 Hz, 1H,
0
0
00
C40eOH), 4.35 (d, J¼15.6 Hz, 1H, CH2ePh), 3.70e3.20 (m, 5H, 4H, H-
10, H-20, H-30, H-40, H-400); 13C NMR (100 MHz, DMSO-d6)
d 181.0
(C]S); 137.4, 128.5 (2C); 127.5 (2C); 126.8 (Ar); 83.7 (C-5), 70.7
(C10), 70.6 (C20); 69.1 (C30); 64.2 (C4); 62.8 (C40); 44.5 (CH2). Anal.
Calcd for C14H20N2O5S$H2O: C, 48.54; H, 6.40; N, 8.09; S, 9.26.
Found: C, 48.49; H, 6.40; N, 7.85; S, 8.42. HRMS: m/z found
328.1072. [Mþ] required for C14H20N2O5S 328.1093.
Compound 4 have Rf 0.62 (CH2Cl2eMeOH 4:1), mp 85e86 ꢁC
Method c. A suspension of 9 (5.0 g, 13.9 mmol) and potassium
thiocyanate (1.37 g, 13.9 mmol) in water (14 mL) was heated 3 h at
100 ꢁC. After cooling, a mixture of 6 and potassium oxalate was
separated (4.04 g). Recrystallization from 70% ethanol (15 mL) gave
pure 6 (2.51 g, 51%).
(decomp.); [
1474 (NH); 1634 (H2O crystallization),20 1015, 970 (CeO); 774 and
727 cmꢀ1 (aromatics); 1H NMR (400 MHz, DMSO-d6)
8.90 (s, 1H,
a
]
D þ45.5 (c 0.5, pyridine); vmax 3480e2980 (OH, NH);
d
NH), 7.34e7.25 (m, 5H, Ar), 5.59 (d, J1,2¼6.6 Hz, 1H, H-1), 5.25 (d,
J3,OH¼5.2, 1H, C3eOH), 4.87 (d, J¼15.6 Hz, 1H, CH2ePh), 4.69 (d,
J5,OH¼6.0 Hz, 1H, C5eOH), 4.52 (d, J¼15.2 Hz, 1H, CH2ePh), 4.39 (t,
J¼5.6 Hz, 1H, C6eOH), 4.02 (d, J1,2¼6.6 Hz, 1H, H-2), 4.00 (d,
J3,4¼2.8 Hz, 1H, H-3), 3.63 (m, 1H, H-5), 3.44 (m, 1H, H-6), 3.33 (m,
4.1.4. N-Benzyl-
synthesized following a minor modification of the published pro-
cedure.30 A suspension of
-mannose (18.0 g, 0.10 mol) and ben-
b-D-mannopyranosylamine (8). This compound was
D
1H, H-4), 3.19 (m, 1H, H-60); 13C NMR (100 MHz, DMSO-d6)
d
182.4
zylamine (10.9 mL, 0.10 mol) in absolute ethanol (50 mL) was
refluxed for 5 min. After cooling, a glassy solid was formed. Solvent
was removed in vacuo and the syrup obtained was dissolved in hot
ethanol (50 mL). The solid separated was filtered and washed with
cool ethanol and ether (22.3 g; 83%); mp 130 ꢁC (lit.30 131e132 ꢁC).
(C]S); 137.9, 128.7 (2C); 128.1 (2C); 127.5 (Ar); 92.3 (C-1), 80.3 (C-
4), 74.5 (C30); 68.7 (C5); 65.1 (C2); 64.2 (C-6); 47.5 (CH2). Anal. Calcd
for C14H18N2O4S$½H2O: C, 52.65; H, 6.00; N, 8.77; S, 10.04. Found:
C, 52.56; H, 6.24; N, 8.51; S, 9.85. HRMS: m/z found 310.0976. [Mþ]
required for C14H18N2O4S 310.0987.
4.1.5. 1-Benzylamino-1-deoxy- -fructopyranose oxalate (9). This
D
4.1.2. (4R,5S)-1-Benzyl-5-hydroxy-4-(
D
-arabino-tetritol-1-yl)imida-
compound (76%) was synthesized following the published pro-
zolidin-2-thione (5). A solution of 3 (0.03 g) in DMSO-d6 (0.5 mL)
cedure.30 M.p 158 ꢁC (lit.30 157e159 ꢁC).
was monitored by 1H NMR, which detected the partial conversion
into (4R,5S)-1-benzyl-5-hydroxy-4-(
zolidin-2-thione (5), being 3 the most stable isomer in the equi-
librium (82%). 1H NMR (400 MHz, DMSO-d6)
8.01 (s, 1H, NH),
D
-arabino-tetritol-1-yl)imida-
4.1.6. 4-(1,2,3,4-Tetra-O-acetyl-D-arabino-tetritol-1-yl)-1-benzylimi-
dazolin-2-thione (11). To a solution of 6 (0.62 g, 2.0 mmol) in pyr-
idine (8.0 mL), cooled at ꢀ20 ꢁC, was added acetic anhydride
(8.0 mL) and the reaction mixture was kept at that temperature for
12 h. Then it was poured into ice-water and the resulting solid was
filtered and washed with cold water and identified as a mixture of
11 and 13 (0.73 g, 78%). Recrystallization from absolute ethanol
d
7.36e7.24 (m, 5H, Ar), 6.52 (d, J5,OH¼7.6 Hz, 1H, C5eOH), 5.26 (d,
J¼15.2, 1H, CH2ePh), 5.00 (t, J4,5¼J5,OH¼7.3 Hz, 1H, H-5), 4.69 (d,
J1 ,OH¼6.8 Hz, 1H, C10eOH), 4.65 (d, J2 ,OH¼6.40 Hz, 1H, C20eOH),
0
0
4.53 (d, J3 ,OH¼7.60 Hz, 1H, C30eOH), 4.40 (t, J4 ,OH¼J4 ,OH¼5.6 Hz,
1H, C40eOH), 4.19 (d, J¼1 5.6 Hz, 1H, CH2ePh), 3.70e3.20 (m, 5H,
4H, H-10, H-20, H-30, H-40, H-400); 13C NMR (100 MHz, DMSO-d6)
0
0
00
gave pure 11; mp 73e75 ꢁC (decomp.); [
form); vmax 3481, 3224 (NH); 1752, 1711 (C]O, ester); 1630 (C]C),
1453, 1372 (CH3), 1217 (CeOeC, ester); 1066, 1040, 1026 (CeO),
3138, 1455, 731, and 637 cmꢀ1 (aromatics); 1H NMR (500 MHz,
a]
ꢀ24.0 (c 0.5, chloro-
D
d
181.8 (C]S); 138.0, 128.0 (2C); 127.2 (2C); 126.4 (Ar); 80.0 (C-5),
70.6 (C10), 70.5 (C20); 67.2 (C30); 63.2 (C4); 59.5 (C40); 44.5 (CH2).
Cl3CD)
d 11.22 (s, 1H, NH), 7.39e7.29 (m, 5H, Ar), 6.58 (s, 1H, H-5),
0
0
0
0
0
0
0
4.1.3. 1-Benzyl-4-(
D
-arabino-tetritol-1-yl)imidazolin-2-thione (6).
5.95 (d, J1 ,2 ¼3.5 Hz, 1H, H-1 ), 5.44 (dd, J1 ,2 ¼3.5 Hz, J2 ,3 ¼8.0 Hz,
0
0
Method a. A solution of 3 (0.274 g, 0.83 mmol) in 30% aqueous acetic
acid (8.5 mL) was heated at w95 ꢁC (external bath) for 30 min. The
mixture was then evaporated to dryness and the residue was
crystallized from 96% aqueous ethanol. The solid afforded was fil-
tered and washed with cold ethanol (0.080 g, 31%). Compound 6
1H, H-20), 5.24 (d, J¼14.5 Hz, 1H,0CH2ePh), 5.19 (ddd, J2 ,3 ¼8.0 Hz,
0
0
0
00
J3 ,4 ¼2.5 Hz, J3 ,4 ¼5.0 Hz,1H, H-3 ), 5.12 (d, J¼14.5 Hz,1H, CH2ePh),
4.25 (dd, J4 ,4 ¼12.5 Hz, J3 ,4 ¼2.5 Hz, 1H, H-40), 4.11 (dd,
0
00
0
0
00
0
00
0
00
J4 ,4 ¼12.5 Hz, J3 ,4 ¼5.0 Hz, 1H, H-4 ), 2.11 (s, 3H, OAc), 2.10 (s, 3H,
OAc), 2.05 (s, 6H, OAc), 13C NMR (125 MHz, Cl3CD)
d 170.5 (2C),169.8
have mp 176e178 ꢁC (decomp.)(lit.31 mp 180e182 ꢁC); [
a
]
D ꢀ17.6 (c
0.5, pyridine); vmax 3500e3000 (OH, NH), 1636 (C]C), 1084e1032
(CeO), 758 cmꢀ1 (aromatics); 1H NMR (400 MHz, DMSO-d6)
11.93
(2C) (CH3CO), 169.4 (C]S), 135.3(Ar), 129.0 (2C, Ar), 128.3 (3C, Ar),
124.1 (C-4), 116.3 (C-5), 70.3 (C20), 68.5 (C30), 64.4 (C10), 61.6 (C40),
50.6 (CH2Ph), 20.7 (2ꢃ CH3CO), 20.6 (2ꢃ CH3CO). Anal. Calcd for
C22H26N2O8S: C, 55.26; H, 5.48; N, 5.86; S, 6.70. Found: C, 55.02; H,
5.46; N, 5.86; S, 6.70. HRMS: m/z found 479.1472. [MþH]þ required
for C22H27N2O8S 479.1488.
d
(s, 1H, NH), 7.35e7.28 (m, 5H, Ar), 6.84 (s, 1H, H-5), 5.15 (d,
J¼14.8 Hz, 1H, CH2ePh), 5.10 (d, J¼14.8 Hz, 1H, CH2ePh), 4.97 (d,
J1 ,OH¼7.20 Hz, 1H, C10eOH), 4.64 (dd, J1 ,2 ¼1.60 Hz, J1 ,OH¼7.20 Hz,
1H, H10), 4.56 (s, 1H, C20eOH), 4.54 (s, 1H, C30eOH), 4.37 (t,
0
0
0
0
J4 ,OH¼J4 ,OH¼5.20 Hz, 1H, C40eOH), 3.57e3.37 (m, 4H, H20, H30, H40,
4.1.7. 3,5,6-Tri-O-acetyl-1-benzyl-(1,2-dideoxy-a-D-glucofurano)[2,1-
0
00
H400); 13C NMR (100 MHz, DMSO-d6)
d
161.7 (C]S); 138.4, 129.6
d]imidazolidin-2-thione (12). To a solution of 4 (0.42 g, 1.3 mmol) in
pyridine (5.0 mL), cooled at ꢀ20 ꢁC, was added acetic anhydride
(3.5 mL) and the reaction mixture was kept at that temperature for
12 h. Then it was poured into ice-water and the resulting white
solid was filtered and washed with cold water and ethanol and
(2C), 129.1 (2C), 128.7 (Ar); 132.1 (C4), 115.9 (C5), 74.2 (C20), 72.2
(C30); 65.3 (C10); 64.5 (C40); 49.8 (CH2). HRMS: m/z found 311.1055.
[MþH]þ required for C14H19N2O4S 311.1066.
From preparative TLC of mother liquors of crystallization (chlor-
oformemethanol, 7:1) compound 4 was isolated (0.093 g, 36%).
identified as 12 (0.43 g, 75%); mp 53e54 ꢁC (decomp.); [
a]
D þ52.0 (c

G. Silvero et al. / Tetrahedron 67 (2011) 7811e7820
7819
McCracken, E.; Hong, C.; Mi, L.; Mao, Y.; Yu-Chieh Wu, J.; Tomita, Y.; Woodrick,
J. C.; Fine, R. L.; Chung, F. J. Med. Chem. 2011, 54, 809e816.
9. For a review in cancer modulation by glucosinolates, see: Das, S.; Tyagi, A. K.;
Kaur, H. Curr. Sci. 2000, 79, 1665e1671.
0.5, chloroform); vmax 3383 (NH); 1749 (C]O, ester); 1230 (CeOeC,
ester); 1045 (CeO) 1455, 723 and 700 cmꢀ1 (aromatics); 1H NMR
(400 MHz, Cl3CD)
d 7.38e7.28 (m, 5H, Ar), 6.50 (s, 1H, NH), 5.67 (d,
10. Shapiro, T. A.; Fahey, J. W.; Wade, K. L.; Stephenson, K. K.; Talalay, P. Cancer
J1,2¼6.40 Hz, 1H, H-1), 5.22 (d, J¼14.8 Hz, 1H, CH2ePh), 5.20 (m, 1H,
Epidemiol., Biomarkers Prev. 2001, 10, 501e508.
H-5), 5.19 (d, J3,4¼2.80 Hz,1H, H-3), 4.42 (d, J¼14.8 Hz,1H, CH2ePh),
11. Goosen, T. C.; Mills, D. E.; Hollenberg, P. F. J. Pharmacol. Exp. Ther. 2001, 296,
198e206.
0
4.41 (dd, J6,6 ¼12.0 Hz, J5,6¼2.4 Hz, 1H, H-6), 4.11 (d, J¼6.4 Hz, 1H, H-
€
12. Kassie, F.; Pool-Zobe, B.; Parzefall, W.; Knasmuller, S. Mutagenesis 1999, 14,
2), 4.06 (dd, J3,4¼2.8 Hz, J4,5¼9.20 Hz, 1H, H-4), 3.97 (dd,
0
595e603.
0
0
J5,6 ¼5.6 Hz, J6,6 ¼12.40 Hz, 1H, H-6 ), 2.06 (s, 3H, OAc), 2.02 (s, 3H,
13. (a) Piacente, S.; Carbone, V.; Plaza, A.; Zampelli, A.; Pizza, C. J. Agric. Food Chem.
2002, 50, 5621e5625; (b) For a review in the role and effects of glucosinolates,
OAc), 1.99 (s, 3H, OAc), 13C NMR (100 MHz, Cl3CD)
d 183.1 (C]S);
ꢀ
ꢀ
170.7 (CH3CO), 169.9 (CH3CO), 169.6 (2C) (CH3CO); 136.2 (C2), 128.8
(2C), 128,6 (2C); 128.1 (Ar); 92.2 (C1), 76.1 (C3), 75.5 (C4), 67.3 (C5);
63.0 (C2); 62.9 (C6); 47.9 (CH2Ph), 20.9, 20.8, 28.7 (3ꢃ CH3CO). Anal.
Calcd for C20H24N2O7S: C, 55.04; H, 5.54; N, 6.42; S, 7.35. Found: C,
54.91; H, 5.47; N, 6.54; S, 7.09. HRMS: m/z found 437.1386. [MþH]þ
required for C20H25N2O7S 437.1382.
see: Zukalova, H.; Vasak, J. Rostl. Vyroba 2002, 48, 175e180.
14. Kruse, H.-P.; Heydenreich, M.; Engst, W.; Schilde, U.; Kroll, J. Carbohydr. Res.
2005, 340, 203e210.
15. Roseman, S. J. Biol. Chem. 2001, 276, 41527e41542.
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4.1.8. 1-Acetyl-5-(1,2,3,4-tetra-O-acetyl-D-arabino-tetritol-1-yl)-3-
benzylimidazolin-2-thione (13). A mixture of 6 (0.62 g, 2.0 mmol) in
pyridine (8.0 mL) and acetic anhydride (8.0 mL) was heated 3 h at
80 ꢁC and then was kept at room temperature for 12 h. Then it was
poured into ice-water and the resulting solid was filtered and
washed with cold water (0.84 g, 78%). The sensitivity of the title
compound to hydrolysis, yielding 11, hampered the preparation of
ꢀ
ꢀ
21. Avalos, M.; Babiano, R.; Cintas, P.; Jimenez, J. L.; Palacios, J. C.; Valencia, C.
Tetrahedron 1994, 50, 3273e3296 and references cited therein.
ꢀ
ꢀ
22. (a) Avalos, M.; Babiano, R.; Cintas, P.; Jimenez, J. L.; Palacios, J. C.; Silvero, G.;
ꢀ
Valencia, C. Tetrahedron 1999, 55, 4377e4400; (b) Avalos, M.; Babiano, R.;
Cintas, P.; Higes, F. J.; Jimenez, J. L.; Palacios, J. C.; Silvero, G.; Valencia, C. Tet-
ꢀ
an analytical sample. 1H NMR (400 MHz, Cl3CD)
d
7.39e7.26 (m, 5H,
rahedron 1999, 55, 4401e4426.
23. (a) Avalos, M.; Babiano, R.; Cintas, P.; Jimenez, J. L.; Palacios, J. C.; Valencia, C.
ꢀ
ꢀ
ꢀ
0
0
0
Ar), 6.47 (s, 1H, H-4), 6.43 (d, J1 ,2 ¼1.6 Hz, 1H, H-1 ), 5.74 (d,
Tetrahedron 1993, 49, 2655e2675; (b) Avalos, M.; Babiano, R.; Cintas, P.;
0
0
0
0
ꢀ
J¼14.8 Hz, 1H, CH2ePh), 5.49 (dd, J1 ,2 ¼1.6 Hz, J2 ,3 ¼9.6 Hz, 01H, H-
Jimenez, J. L.; Palacios, J. C.; Valencia, C. Tetrahedron 1993, 49, 2676e2690.
20), 5.21 (ddd, J2 ,3 ¼9.6 Hz, J3 ,4 ¼2.4 Hz, J3 ,4 ¼5.2 Hz, 1H, H-3 ), 4.72
24. Bock, K.; Pedersen, C. Adv. Carbohydr. Chem. Biochem. 1983, 41, 27e66.
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1247e1254; (b) Lewin, A. H.; Lipowitz, J.; Cohen, T. Tetrahedron Lett. 1965, 6,
1241e1245.
0
0
0
0
0
00
0
00
0
0
(d, J¼14.8 Hz, 1H, CH2ePh), 4.22 (dd, J4 ,4 ¼12.8 Hz, J300,4 ¼2.4 Hz, 1H,
H-40), 4.14 (dd, J4 ,4 ¼12.8 Hz, J3 ,4 ¼5.2 Hz, 1H, H-4 ), 3.14 (s, 3H,
0
00
0
00
NAc), 2.10 (s, 3H, OAc), 2.08 (s, 3H, OAc), 2.04 (s, 3H, OAc), 1.66 (s,
ꢀ
ꢀ
27. Avalos, M.; Jimenez, J. L.; Palacios, J. C.; Ramos, M. D.; Galbis, J. A. Carbohydr. Res.
3H, OAc); 13C NMR (100 MHz, Cl3CD)
d
173.7, 170.5, 170.1, 169.8 (4ꢃ
1987, 161, 49e64.
ꢀ
CH3CO), 167.2 (C]S), 135.8 (Ar), 129.8 (2C, Ar), 129.2, 128.7 (2C, Ar),
126.5 (C-5), 118.2 (C-4), 69.4 (C10), 68.8 (C20), 67.3 (C30), 62.9 (C40),
51.4 (CH2Ph), 28.9 (CH3CON), 21.5, 21.4, 21.3, 20.8 (4ꢃ CH3CO).
ꢀ
ꢀ
28. Avalos, M.; Cintas, P.; Gomez, I. M.; Jimenez, J. L.; Palacios, J. C.; Rebolledo, F.;
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Acknowledgements
Financial support from the Junta de Extremadura (PRI08A032)
and the Ministry of Education and Science (CTQ2010-18938/BQU
and CTQ2007-66641/BQU) is gratefully acknowledged.
33. A similar behaviour has been found in 1-amino-1-deoxyketoses: (a) Jochims, J.
C. Angew. Chem., Int. Ed. Engl. 1966, 5, pp 964; (b) Dalton, L. K. Aust. J. Chem.
1966, 19, 445e450.
ꢀ
€
€
34. Kovacs, J.; Pinter, I.; Messmer, A.; Toth, G.; Lendering, U.; Koll, P. Carbohydr. Res.
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Supplementary data
35. However, silver cyanate gives only furanoid structures as 18: Galbis, J. A.; Za-
mora, F.; Turmo, P. Carbohydr. Res. 1987, 163, 132e135.
36. García, F.; Bolanos, F. Anales Real Soc. Esp. Física
233e242.
Schemes S1eS4 and Figs. S1eS15. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.tet.2011.07.073.
~
y Química 1948, 44B,
37. (a) Odo, K.; Kono, K.; Sugino, K. J. Org. Chem. 1958, 23, 1319e1321; (b) Areces, P.;
ꢀ
Fernandez, J. I.; Fuentes, J.; Galbis, J. A. Carbohydr. Res. 1990, 198, 363e367.
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E.; Cutting, J.; Dupont, W.; Kruse, L.; Silberman, L.; Thomas, R. C. J. Chem. Soc.,
Chem. Commun. 1976, 736e738; (c) Baldwin, J. E.; Thomas, R. C.; Kruse, L.;
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Chem. Soc., Chem. Commun. 1977, 233e235; (e) Baldwin, J. E.; Lusch, M. J.
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