Electrochemical synthesis of glycoconjugates of 3β-hydroxy- Δ5-steroids by using non-activated sugars and steroidal thioethers

Article abstract of DOI:10.1016/j.tet.2013.07.106

A new protocol for the electrochemical synthesis of glycoconjugates is presented. Thioether derivatives of cholesterol and other sterols were subjected to anodic oxidation in the presence of a sugar alcohol affording glycoconjugates with the sugar linked to a steroid moiety by an ether bond. The isomeric 6β-3α,5α-cyclo-steroidal thioethers proved to be better sterol donors than the normal 3β-Δ⁵-steroidal thioethers.

Full text of DOI:10.1016/j.tet.2013.07.106

Tetrahedron 69 (2013) 8904e8913
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Electrochemical synthesis of glycoconjugates of 3b -
-hydroxy-D5
steroids by using non-activated sugars and steroidal thioethers
Aneta M. Tomkiel a, Krzysztof Brzezinski a, Zenon qotowski a, Leszek Siergiejczyk a,
a
a
b
b
ꢀ
Piotr Wa1ejko , Stanis1aw Witkowski , Jan Kowalski , Jolanta P1oszynska ,
Andrzej Sobkowiak b, Jacek W. Morzycki a
a Institute of Chemistry, University of Białystok, Hurtowa 1, 15-399 Białystok, Poland
,
*
b
ꢀ
ꢀ
Faculty of Chemistry, Rzeszow University of Technology, P.O. Box 85, 35-959 Rzeszow, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 May 2013
Received in revised form 17 July 2013
Accepted 30 July 2013
Available online 15 August 2013
A new protocol for the electrochemical synthesis of glycoconjugates is presented. Thioether derivatives
of cholesterol and other sterols were subjected to anodic oxidation in the presence of a sugar alcohol
affording glycoconjugates with the sugar linked to a steroid moiety by an ether bond. The isomeric 6
,5 -cyclo-steroidal thioethers proved to be better sterol donors than the normal 3
5-steroidal
thioethers.
b-
3a
a
b-D
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Glycosylation
Cholesterol
Electrochemical oxidation
Thioethers
Glycoconjugates
1. Introduction
Other chemists have also investigated cholesterol electro-
oxidation, but mostly using indirect methods with various media-
tors. An interesting, though low-yielding, electrochemical method
of cholesterol side-chain oxidation at the tertiary position (C25)
was described by the Takayama group.4 The selective reaction
was achieved with the Tl/(TFA)3-hematoporphyrin-O2-cathodic
reductive system. A hydroxyl radical was suggested as an active
species in this system. The same group has also described anodic
oxidation of cholesterol in dichloromethane solution with various
additives, leading mostly to chlorinated products.5 Takeya et al.
have described6 an electrochemical system for stereoselective al-
lylic hydroxylation of cholesteryl acetate with dioxygen induced by
iron picolinate complexes. There is also one report on direct anodic
oxidation of cholesterol at a carbon electrode in acetonitrile.7,8 The
reaction afforded cholesta-4,6-dien-3-one in a high yield. This ex-
ample shows that electrochemical oxidation reactions can be useful
since they are controllable by electrolysis conditions, including the
potential applied, and are relatively cheap due to the low cost of
electric energy used when compared with chemical reagents.
Electrochemical reactions can also be applied to the synthesis of
glycosides.9 The first electrochemical method of synthesis of gly-
cosides was developed by Noyori, who used aryl glycosides as
glycosyl donors.10 The method was later improved by using aryl
thioglycosides instead, i.e., compounds that undergo electro-
oxidation at a lower potential.11e14 Electrochemical oxidation of
In recent years our group has studied the direct electrochemical
oxidation of cholesterol under various conditions. The products of
oxidation of cholesterol, the most common steroid in the animal
kingdom, are present in food due to lipid oxidation reactions in the
presence of oxygen, exposure to sunlight, food processing, etc. Such
compounds reveal cytotoxic, apoptotic, and pro-inflammatory ac-
tivity.1 Therefore, they are intensively studied by chemists and
toxicologists. From the chemical point of view cholesterol is
a homoallylic alcohol with a relatively large hydrophobic moiety.
The site of cholesterol electrooxidation largely depends on the
reaction conditions. We have found that a reaction carried out in
acetic acid as a solvent affords products of acetoxylation at the al-
lylic position (C7).2 In dichloromethane, products chlorinated at the
double bond are produced, unless an electrolyzer with separated
electrode compartments is used.3 Then the one electron oxidation
of cholesterol occurs at the oxygen atom to afford a radical cation.
The subsequent cleavage of the CeO bond affords HOꢀ and a car-
bocation, which reacts with nucleophiles present in the reaction
mixture, leading to various products.
* Corresponding author. Tel.: þ48 85 7457585; fax: þ48 85 7457581; e-mail
address: morzycki@uwb.edu.pl (J.W. Morzycki).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.07.106

A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
8905
these compounds has been shown to follow an overall EC-type, in
which the electro-generated cation radical (electrochemical step)
undergoes an irreversible carbonechalcogen bond rupture
(chemical step) to produce the corresponding glycosyl cation,
which reacts with alcohol. The formal oxidation potentials were
found to vary according to the identity of the chalcogenide, such
that OPh>SPhwSTol>SePh.15 Selective electrochemical glycosyla-
tion by reactivity tuning has been attempted.16 The reactions were
carried out in a suitable supporting electrolyte or in the presence
of a small amount of mediator, such as NBS, Br2,17 tris-(4-
bromophenyl) ammoniumyl hexachloroantimonate18 or a support-
ing electrolyte, e.g., trifluoromethanesulfonate.17
electrolyses are performed in solvents containing water.22,23 The
alternative reaction pathways24 consist of CaeH deprotonation of
the intermediate cation radical or the substitution of the aryl ring at
the p-position. The former reaction is strongly favored in acetic acid
as a solvent and is more likely to occur in the case of the less bulky
alkyl groups, while the latter reaction can be suppressed by using p-
substituted aryl thioether.25
In the case of sterol thioethers (cholesteryl aryl sulfides were
chosen as model compounds), cleavage of the CeS bond is also
likely to occur since the resulting carbocation is mesomerically
stabilized due to the presence of a homoallylic double bond
(Scheme 2). However, in the case of saturated steroid derivatives,
the analogous cleavage is not a favored step and electrooxidation
follows a different pathway, or no reaction is observed.
2. Results and discussion
Fig. 1 indicates that all of the sterol thioesters (cholesteryl
We recently described a new electrochemical method of glyco-
phenyl sulfide 1a, cholesteryl p-tolyl sulfide 1b, 3
a
,5
a
-cyclo-
-yl
sylation of 3
b
-hydroxy-
D
5-steroids using non-activated sugars.19 The
cholestan-6 -yl phenyl sulfide 2a, and 3 ,5 -cyclocholestan-6b
b
a
a
method consisted in electrooxidation of sterol (e.g., cholesterol) in
the presence of a sugar in a non-polar solvent, such as dichloro-
p-tolyl sulfide 2b), which were chosen for preparative electrolysis
in this study are electroactive in the potential region where the
preparative processes occur. Cholesteryl phenyl sulfide (1a, black
curve) and cholesteryl p-tolyl sulfide (1b, blue curve) form well-
developed anodic peaks at potentials þ1.44 V and þ1.24 V (vs Ag/
methane. The initially formed cation radicals (steroid-OH)þ un-
ꢀ
dergo splitting into a steroidal carbocation and a hydroxyl radical. In
the presence of a sugar alcohol the carbocation is trapped by a hy-
droxyl group to form ethers. In such a way various glycoconjugates
(including glycosides) may be prepared, though in rather low yields.
There are several reasons why the reaction yields are not satisfac-
tory. One is the formation of disteroidal ethers, which are formed as
a result of the reaction of the starting sterol with the carbocation.
Therefore, a large excess of a sugar substrate should be used to avoid
the formation of these unwanted products. Some by-products are
formed due to the relatively high potential needed for the oxidation
of sterols. Finally, the hydroxyl radicals or hydrogen peroxide that
are produced during sterol electrooxidation may lead to various side
reactions. The aim of this study is to improve the efficiency of the
electrochemical glycosylation method by using activated sterol de-
rivatives. Since the glycosyl thioethers were successfully applied for
glycosylation reactions as mentioned above, we attempted to use
aryl thioether derivatives of sterols as potential donors of a steroid
moiety in the synthesis of steroid glycoconjugates.
Electrochemical oxidation of non-steroidal alkyl aryl sulfides
(ArSR) has previously been studied.20,21 The products of these re-
actions are remarkably dependent upon the structure of R, the
polarity of the solvent, and the supporting electrolyte. If R can yield
stabilized carbocations like benzyl or triphenylmethyl cations,
extensive cleavage of the CeS bond occurs during oxidation
(Scheme 1). With other R groups the corresponding sulfoxides or
sulfones are obtained in good yields, especially when the
0.1 M AgNO3 in MeCN), respectively. 3
a
,5a
-Cyclocholestan-6
b-yl
phenyl sulfide (2a, red curve) and 3 ,5
a
a
-cyclocholestan-6b
-yl p-
tolyl sulfide (2b, green curve) give broad oxidation peaks with the
main peak potentials equal to þ1.47 V and þ1.27 V for (2a) and (2b),
respectively. All of the peaks are irreversible and no cathodic peaks
are present in the subsequent cathodic scans. It is worth noting that
cholesteryl phenyl ether is also oxidized under the same experi-
mental conditions. Its anodic peak potential is equal to 1.65 V.
The study on glycosylation using aryl sulfide derivatives of ste-
rols (Scheme 3) was preceded by attempts with cholesteryl phenyl
ether. Electrooxidation of this compound with a model sugar,
1,2:3,4-di-O-isopropylidene-a-D-galactopyranose (3), containing
the free OH group at the primary position, was carried out in
dichloromethane. However, the expected glycoconjugate 4 was
obtained only in trace amounts due to a very low conversion.
Then cholesteryl phenyl sulfide (1a) was prepared by reaction of
cholesteryl p-tosylate with ten equivalents of thiophenol in dioxane
at reflux. Electrochemical oxidation of 1a in the presence of an
equimolar amount of the galactose derivative 3 (run 1) in dichloro-
methane afforded product 4 (12%) along with its regioisomer 5 (2%).
However, almost half of the starting cholesteryl phenyl sulfide (1a)
was recovered unchanged. Isolation of the i-steroidal glycoconjugate
5 is a direct proof that the non-classical carbocation is an in-
termediate in the reaction. In addition to steroidal products,
-
.
+ Nu
+
2
PhCH Nu + (PhS)
2
PhCH
+ SPh
2
-
-
.
- e
+
+ H O
2
+ Nu
PhCHSPh
PhCH SPh
2
+
- H
- NuH
-
O
.
Nu
+
[PhCH SPh]
2
-
-
+
.
- e
+ Nu
- H
PhCHSPh
PhCHSPh
Nu
-
-
H
- e
+ Nu
.
PhCH S
2
PhCH S
2
Nu
+
- H
Nu
Scheme 1. Alternative electrooxidation pathways of benzyl phenyl sulfides.26

8906
A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
.
- e-
- ArS
+
ArS
ArS
+
.
+
Scheme 2. Expected electrooxidation pathway of sterol thioethers.
was not 2a used as the starting material but the isomeric choles-
teryl phenyl sulfide 1a. This means that isomerization between the
thioethers occurs during the electrochemical reaction. Of course,
diphenyl disulfide was also the product of reaction.
In the subsequent electrochemical reactions trifluoroacetic acid
was not used but instead anionite (Dowex) was added to remove
chlorides. The reaction was carried out in a divided H-cell, in which
the cathodic and anodic compartments were separated by a glass frit.
A shorter reaction time was applied (run 3) to avoid consecutive
reactions, but it resulted in lower conversion (26% of thioether was
recovered). The major reaction product 4 (34%) was accompanied by
several minor by-products, including the isomeric glycoconjugate 5,
cholesterol 6, dicholesteryl ether 7, and cholesteryl chloride 8. When
the electrolysis time was extended to almost 2 h and higher am-
perage was used (run 4), a complex mixture of products was obtained
consisting of glycoconjugates 4 and 5, cholesterol 6, dicholesteryl
ether 7, cholesteryl chloride 8, diene 10, and diphenyl disulfide (11).
Analogously to 2a,
6b-p-tolylsulfanyl-3a,5a-cyclocholestane
(2b) was obtained from cholesteryl p-tosylate and p-toluenethiol.
The galvanostatic electrolysis (7.5 mA, 4000 s) of 2b (run 5) with
1,2:3,4-di-O-isopropylidene-a-D-galactopyranose (3) afforded a 52%
Fig. 1. Cyclic voltammograms registered in 0.2
fluoroborate (TBABF4), in dichloromethane on a platinum electrode (area, 0.03 cm2) of
cholesteryl phenyl sulfide (1a, black), cholesteryl p-tolyl sulfide (1b, blue), 3 ,5 -cy-
clocholestan-6 -yl phenyl sulfide (2a, red), and 3 ,5 -cyclocholestan-6 -yl p-tolyl
M tetrabutylammonium tetra-
yield of 4 and 1% of 5. The other reaction products were: the rear-
ranged thioether 1b (22%), cholesterol 6 (7%), and di-p-tolyl disul-
fide (12). Slightly worse results (run 6) were at a higher current
(10 mA) and shorter reaction time (3000 s). In all the experiments
described so far the equimolar amounts of reagents (steroidal thio-
ether and sugar) were used. When thioether 2b was used in excess
(three times), the yield of the glycoconjugate 4 (calculated for the
sugar substrate) was not any better (run 7).
a
a
b
a
a
b
sulfide (2b, green). Concentrations of all compounds are equal to 5 mM. Scan rate
1 V sꢁ1, potentials were measured versus Ag/0.1 M AgNO3 in acetonitrile.
diphenyl disulfide 11 was also isolated from the reaction mixture.
This may suggest that PhSꢀ radicals are formed during the reaction
by a splitting of the initially formed sulfur-centered cation radicals
into non-classical carbocations and sulfur radicals.
The electrochemical reaction of 1a with 3 afforded the desired
glycosylation product, but neither the reaction yield nor the con-
version was satisfactory. Therefore, in the next attempts more re-
active i-steroidal aryl sulfides were used as steroid moiety donors.
In the next experiment optimized electrochemical reaction
conditions (7.5 mA, 4000 s) were applied to the synthesis of a gly-
coconjugate with cholesteryl linked to the secondary hydroxyl
group of a sugar moiety (Scheme 4). The electrolysis of 6
ylsulfanyl-3 ,5 -cyclocholestane (2b) in the presence of an equi-
molar amount of 1,2:5,6-di-O-cyclohexylidene- -glucofuranose
b-p-tol-
a
a
D
Preparation of 6
b
-phenylsulfanyl-3
a
,5
a
-cyclocholestane (2a) and
(13) afforded the expected glycoconjugate 14, but only in a 12%
yield. The other steroidal products were: cholesterol 6 (8%), cho-
lesteryl chloride 8 (1%), and diene 10 (2%). The rearranged thioether
1b was obtained in a 35% yield.
The reactions studied so far led to glycoconjugates with a sugar
linked to a steroid moiety by an ether bond. For the synthesis of
glycosides with an acetal linkage, the sugar substrate with an un-
protected anomeric position was taken, i.e., 2,3,4,6-tetra-O-benzyl-
other i-steroidal aryl sulfides from the corresponding sterol
p-tosylates and aryl thiol required buffering of the reaction mixture
by addition of potassium acetate. In the case of the reaction of
cholesteryl p-tosylate with thiophenol in the presence of AcOK,
a mixture of thioethers at C-6 (compound 2a) and C-3 (compound
1a) was formed in the ratio 7:1. Separation of these products was
not simple since both proved to be very non-polar. However, it was
achieved by slow elution from the silica gel column with hexane.
The electrochemical oxidation of 2a in the presence of 1,2:3,4-
D
-glucopyranose (15). The electrochemical reaction was carried out
under the same conditions as in the previous case. The reaction
appeared to be not very stereoselective, and both anomers and
b were obtained in the ratio 4:1 (Scheme 5). The chemical yield of
di-O-isopropylidene-
a
-D
-galactopyranose (3) was carried out in
a
a similar manner as for 1a (run 2). The conversion was much better
than in the previous case and the desired glycoconjugate 4 was
obtained in a 40% yield accompanied by minor amounts of its
regioisomer 5 and cholesteryl trifluoroacetate 9. The latter com-
pound was formed by reaction with trifluoroacetic acid, which was
added to the cathodic compartment of the electrolyzer to prevent
the electrochemical reduction of dichloromethane. It was proven in
a previous paper3 that the chlorides formed in this process are
responsible for the side reactions of cholesterol. Interestingly, the
steroidal thioether that was recovered from the reaction mixture
glycosides amounted to only 20%. These were separated and the
pure compounds were proven to be identical in all respects with
the corresponding anomers of cholesteryl 2,3,4,6-tetra-O-benzyl-D-
glucopyranosides (16a and 16b) as reported in the literature.27 In
addition to cholesteryl glycosides 16a and 16b, several by-products,
cholesterol 6 (8%), cholesteryl chloride 8 (1%), and cholesteryl
p-tolyl sulfide (1b), were obtained.
With the conditions optimized for the synthesis of cholesteryl
glycoconjugates, analogous electrochemical reactions were

A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
8907
OH
O
O
O
+
Anodic oxidation
O
O
S
1a: R = H
3
b: R = CH3
O
O
O
O
OH
R
O
O
O
Anodic oxidation
O
O
4
+
O
O
3
S
2a: R = H
b: R = CH3
R
By-products:
R
S
S
R
X
O
O
11: R = H
12: R = CH3
6: X = OH
10
O
O
7: X = O-cholesteryl
8: X = Cl
O
9: X = OCOCF3
O
5
Examples of glycosylation reactions (only steroidal products are shown):
a
1a
4 (12%) + 5 (2%) + 1a (48%)
run 1
run 2
run 3
run 4
run 5
a
2a
4 (40%) + 5 (1%) + 1a (12%) + 9 (3%)
b
c
2a
2a
4 (34%) + 5 (1%) + 1a (26%) + 6 (1.5%) + 7 (1%) + 8 (3%)
4 (12%) + 5 (<1%) + 1b (23%) + 6 (9%) + 7 (3%) + 8 (3%) + 10 (2%)
4 (52%) + 5 (1%) + 1b (22%) + 6 (7%)
b
2b
d
e
2b
2b
4 (38%) + 5 (<1%) + 1b (21%) + 6 (2%)
4 (31%) + 5 (1.5%) + 1b (23%) + 6 (7%)
run 6
run 7
Scheme 3. Electrochemical glycosylation of sterol thioethers. Reaction conditions: aed) 1a, 2a or 2b (0.37 mmol), 3 (0.36 mmol); a) current 5 mA, time 6000 s, 0.1 M TBABF4/CH2Cl2
(3.5 mL), 0.5 mM CF3COOH, molecular sieves; b) current 7.5 mA, time 4000 s, 0.1 M TBABF4/CH2Cl2 (3.5 mL), anionite, molecular sieves; c) current 10 mA, time 6600 s, 0.1 M TBABF4/
CH2Cl2 (3.5 mL), anionite, molecular sieves; d) current 10 mA, time 3000 s, 0.1 M TBABF4/CH2Cl2 (3.5 mL), anionite, molecular sieves; e) 2b (0.61 mmol), 3 (0.20 mmol), current
9 mA, time 2400 s, 0.1 M TBABF4/CH2Cl2 (3.5 mL), anionite, molecular sieves.
performed with i-steroidal thioethers derived from diosgenin and
methyl 3 -hydroxy-5-cholen-24-oate. The corresponding steroi-
dal donors (3 ,5 -cyclosteroid-6 -p-tolyl sulfides 17 and 21)
were obtained in the usual way by solvolysis of sterol p-tosylates
in the presence of p-tolylthiol, albeit in low yields and used as
sterol donors. The electrochemical reactions (Schemes 6 and 7)
performed under optimized conditions (7.5 mA, 3600 s) yielded
glycoconjugates 18 and 22 (30% and 17%, respectively).
Apart from the diosgenin glycoconjugate 18, the electrochemical
reaction (Scheme 6) afforded aglycone (diosgenin 19) and the
rearranged p-tolyl sulfide 20. The structure of the diosgenin gly-
coconjugate 18 was confirmed by X-ray diffraction analysis (Fig. 2).
b
a
a
b

8908
A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
H
O
O
O
O
O
O
O
Anodic oxidation
O
+
2b
+
6 (8%)
+
8 (1%)
+
10 (2%)
+
1b (35%)
O
O
13
O
O
14 (12%)
Scheme 4. Electrochemical reaction of 1,2:5,6-di-O-cyclohexylidene-D-glucofuranose (13).
OBn
O
BnO
O
BnO
OBn
16a (16%)
Bn
O
O
O
Anodic oxidation
BnO
BnO
+ 2b
OBn
OH
15
Bn
O
O
BnO
BnO
Bn
O
16b (4%)
Other steroidal products: 6 (8%), 8 (1%), 1b (21%)
Scheme 5. Electrochemical reaction of 2,3,4,6-tetra-O-benzyl-D-glucopyranose (15).
O
O
O
O
18 (30%)
O
O
O
O
O
O
OH
O
O
O
O
Anodic oxidation
O
+
O
O
HO
3
O
19 (4%)
S
17
O
S
20 (33%)
Scheme 6. Electrochemical synthesis of diosgenin glycoconjugate.

A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
8909
Fig. 2. Molecular structure of 18. Displacement ellipsoids are drawn at the 50% probability level. The figure was prepared with OLEX2.28
Similarly, the reaction of methyl 6
b
-p-tolylsulfanyl-3
a,5a
-cyclo-
It seems that diaryl disulfide, which is formed during the reaction,
cholanoate (21) in addition to the methyl 3
oate glycoconjugate 22 yielded the isomeric p-tolyl sulfide 23
(Scheme 7).
b
-hydroxychol-5-en-24-
competes with a sugar nucleophile for access to the carbocation.
Unfortunately, it seems that electric energy is only needed to ini-
tiate the process, and then the isomerization occurs as a chemical
COOMe
O
O
22 (17%)
O
O
COOMe
O
O
OH
O
O
COOMe
Anodic oxidation
O
+
O
O
S
3
21
S
23 (23%)
Scheme 7. Electrochemical synthesis of methyl 3b-hydroxychol-5-en-24-oate glycoconjugate.
In all the glycosylation experiments that were performed the
starting ,5 -cyclosteroid-6 -yl aryl sulfides completely dis-
appeared during electrochemical reactions (even if a large excess of
a sterol donor was used). The isomeric sterol aryl sulfides (with an
arylsulfanyl group at C-3) were isolated instead in substantial
chain reaction. The key step is the addition of highly thiophilic ArSþ
to sterol aryl sulfide followed by cleavage of the C(6)eS bond
leading to the non-classical carbocation and diaryl disulfide.29 Such
a mechanism explains why the use of an excess of the reactive
3a
a
b
6b-sulfide is not effective since it is being consumed in the isom-
amounts. However, these isomeric 3b-sterol aryl sulfides, as has
erization process affording the inert 3 -sulfide.
b
been shown in the preliminary reactions, are much less efficient as
sterol donors. The most likely the isomerization occurred during
electrolysis. A blank reaction of 6b-p-tolylsulfanyl-3a,5a-cyclo-
A series of blank experiments proved that the electrochemical
activation of sterol aryl sulfides is much more efficient than that
using chemical promoters. Attempts to synthesize glycoconjugates
cholestane (2b) carried out under the same conditions (7.5 mA) as
those employed for glycosylation reactions but in the absence of
sugar confirmed this assumption. A sample of the reaction mixture
taken after 600 s contained equal amounts of isomeric sulfides, the
using 6b-p-tolylsulfanyl-3a,5a-cyclosteroid donors failed. However,
simple ethers (methyl or ethyl) were prepared in moderate yields
from methanol or ethanol, respectively. Reactions with a large excess
of alcohol (50 equiv) were carried out in dichloromethane in the
presence of molecular sieves at room temperature with N-bromo-
succinimide or trimethylsilyl trifluoromethanesulfonate as activa-
tors. There was almost no reaction with secondary alcohols (e.g.,
cyclohexanol).
second sample taken 600 s later showed the ratio 4:1 in favor of 3b-
p-tolylsulfanylcholest-5-ene (1b), while after the next 600 s time
interval the starting sulfide 2b completely disappeared. The tenta-
tive mechanism of this isomerization is presented in Scheme 8.

8910
A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
C8H17
.
- e-
- ArS
ArS-SAr
ArS+
.
S
-
2 ArS
ArS-SAr
+
.
+
S
+
S
Ar
Ar
Ar
C8H17
C8H17
ArS-SAr
ArS+
ArS+
S
etc.
-
-
ArS-SAr
+
+
Ar
S
S
+
S
Ar
Ar
Ar
Scheme 8. Isomerization of aryl sulfides during electrolysis.
3. Conclusions
TLC and stopped when no further increase in the concentration of
glycosylation products was observed. A divided H-cell was used in
which the cathodic and anodic compartments (3.5 mL of electro-
lytes each) were separated by a glass frit. In all the measurements
0.1 M solution of tetrabutylammonium tetrafluoroborate (TBABF4,
from Aldrich) in dichloromethane was used as a supporting elec-
trolyte. The steroid and sugar substrates were introduced into the
anodic compartment together with a 0.3 g of 3A molecular sieve to
eliminate traces of water, whereas anionite (1.5e2 g, Dowex 2x8,
200e400 mesh, perchlorate form) was placed in the cathodic
compartment to eliminate chloride ions from forming by the re-
duction of dichloromethane. The solutions in both compartments
were stirred during electrolysis and additionally a continuous
flow of argon was applied in the anodic compartment. A platinum
mesh was used as a cathode and a platinum plate (2ꢃ1.5 cm) was
used as an anode. All measurements were performed at room
temperature.
A new electrochemical method of synthesis of sterol glyco-
conjugates was developed. The method does not require activation
of a sugar substrate. Sterol is activated by formation of the corre-
sponding aryl sulfide. However, C-3 aryl sulfides proved to be in-
sufficiently reactive in the electrochemical processes. Therefore,
isomeric 3
tested as sterol donors in the electrochemical reactions. 6
ylsulfanyl-3 ,5 -cyclosteroids proved superior to -phenyl-
sulfanyl-3 ,5 -cyclosteroids in this respect. With these sulfides,
a
,5a
-cyclosteroid-6
b
-yl aryl sulfides were prepared and
b
-p-Tol-
a
a
6b
a
a
moderate to good yields of glycoconjugates were achieved and
lesser amounts of by-products were formed. The described elec-
trochemical method is better suited for the construction of glyco-
conjugates (ethers) from sugar primary alcohols than from sugars
with the hydroxyl group at the secondary or anomeric positions. It
was proven that rapid isomerization of reactive 6b- to inert 3b-
sulfides occurs during electrolysis, and for this reason conversions
achieved in many cases were unsatisfactory. Further study on the
electrochemical glycosylation of sterols is in progress.
The sugar substrates (1,2:5,6-di-O-cyclohexylidene-
anose,30 2,3,4,6-tetra-O-benzyl- -glucopyranose,31 and 1,2:3,4-di-
-galactopyranose32) were prepared according
D-glucofur-
D
O-isopropylidene-a-D
to known procedures.30e32
4. Experimental section
4.1. General methods
Melting points were determined on a Toledo Mettler-MP70
apparatus. 1H and 13C NMR (400 and 100 MHz, respectively)
spectra were recorded on a Bruker Avance II spectrometer in CDCl3
solutions with TMS as the internal standard (only selected signals
in the 1H NMR spectra are reported). Infrared spectra were recor-
ded on a Nicolet series II Magna-IR 550 FTIR spectrometer in
chloroform solutions. Mass spectra were recorded at 70 eV with
a time-of-flight (TOF) AMD-604 spectrometer with electrospray
ionization (ESI) or AutoSpec Premier (Waters) (EI). Optical rotations
were measured on a PerkineElmer 141 polarimeter at the sodium
D-line (589 nm).
Merck Silica Gel 60, F 256 TLC aluminum sheets were applied for
thin-layer chromatographic analysis. For a visualization of the
products a 5% solution of phosphomolybdic acid in ethanol was
used. The reaction products were separated by column chroma-
tography performed on a 70e230 mesh silica gel (J.T. Baker).
Cyclic-voltammograms were recorded with iR compensation at
25 ꢂC using a three-electrode potentiostat (Bioanalytical Systems
Model CV-50W). The experiments were conducted in a 15-mL
electrochemical cell with an argon-purge system. The working
electrode was a Bioanalytical Systems platinum inlay (diameter,
1 mm), the auxiliary electrode a platinum mesh (contained in
a glass tube with a medium porosity glass frit), and the reference
electrode Ag/0.1 M AgNO3 in acetonitrile. The latter was contained
in a Pyrex tube with a cracked softglass tip, which was placed inside
a Luggin capillary. Before each experiment the working electrode
was polished using a Buehler Micropolish Alumina Gamma 3B and
Buehler Microcloth polishing cloth, rinsed with dichloromethane,
and dried. The accuracy of potential measurement was equal to
10 mV. All reported values of potentials and currents are means of
three independent measurements.
4.1.1. X-ray diffraction analysis of 18. Crystals suitable for X-ray dif-
fraction studywere obtainedat roomtemperature byslowevaporation
from a hexane solution. The X-ray diffraction data were collected at
100(2) K on a SuperNova diffractometer (Agilent) with a CCD detector
The preparative electrolyses were performed with a potentio-
stat/galvanostat (Princeton Applied Research Model Parstat 2273)
under galvanostatic conditions using a current equal to 5e10 mA
and the reaction time 2000e6000 s. The current applied was the
maximum current available for the used electrolysis setup (power
supply and ohmic resistance). The reactions were monitored by
and CuK radiation. The crystal structure was solved using direct
a
methods with SHELXD and refined with SHELXL.33 Allhydrogenatoms
were initially located in electron-density difference maps and were
ꢁ
constrained to idealized positions, with CeH¼0.95e1.00 A and with

A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
8911
Uiso(H)¼1.5Ueq(C) for the methyl hydrogen atoms and Uiso(H)¼
1.2Ueq(C) for others. The non-hydrogen atoms were refined aniso-
tropically. Crystal data for (18): C39H60O8, Mr¼656.87, colorless needle,
0.80ꢃ0.15ꢃ0.10 mm3, orthorhombic space group P212121,
136.9 (C),132.6 (CH),130.8 (C),129.6 (CH),120.8 (CH),109.3 (C), 80.8
(CH), 66.8 (CH2), 62.1 (CH), 56.5 (CH), 50.2 (CH), 47.8 (CH), 41.6 (CH),
40.3 (C), 39.8 (CH2), 39.63 (CH2), 39.59 (CH2), 37.0 (C), 32.0 (CH2),
31.8 (CH2), 31.39 (CH2), 31.36 (CH), 30.3 (CH), 29.5 (CH2), 28.8 (CH2),
21.1 (CH3), 20.7 (CH2), 19.4 (CH3), 17.1 (CH3), 16.3 (CH3), 14.5 (CH3);
EIMS, m/z: 520 (Mþ, 72%), 397 [(Mꢁp-CH3C6H4S)þ, 100%]; HRMS
(EI): m/z calcd for C34H48O2S: 520.3375; found 520.3366.
3
ꢁ
ꢁ
ꢁ
ꢁ
a¼10.61462(9) A,b¼11.07419(12) A, c¼30.5223(3) A, V¼3587.85(6) A ,
Z¼4, rcalcd¼1.216 g cmꢁ3
,
m
¼0.67 mmꢁ1, F(000)¼1432, R1¼0.0278,
wR2¼0.0689, 3600 independent reflections, qmax¼68.3ꢂ, qmin¼2.9ꢂ,
432 parameters, and 0 restraints. CCDC-930074 contains the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
4.2.1.3. Methyl
solid; Rf¼0.54 (AcOEt/hexane 1:9); [
nmax: 1731, 1492, 1172, 1102, 1018 cmꢁ1
3
b
-p-tolylsulfanylchol-5-enoate
(23). White
20
a
]
;
ꢁ8.4 (c 1.0, CHCl3); IR,
D
1H NMR,
d (ppm): 7.32 (d,
2H, J¼8.0 Hz, HeAr), 7.10 (d, 2H, J¼8.0 Hz, HeAr), 5.30 (m, 1H, H-6),
3.67 (s, 3H, Hemethyl ester), 2.94 (m, 1H, H-3 ), 2.34 (s, 3H,
HeAreCH3), 0.99 (s, 3H, H-19), 0.94 (d, 3H, J¼6.4 Hz, H-21), 0.69 (s,
3H, H-18); 13C NMR,
(ppm): 174.7 (C), 141.8 (C), 136.9 (C), 132.6
(CH), 130.9 (C), 129.5 (CH), 121.0 (CH), 56.7 (CH), 55.8 (CH), 51.4
(CH3), 50.3 (CH), 47.8 (CH), 42.4 (C), 39.72 (CH2), 39.64 (CH2), 39.62
(CH2), 36.8 (C), 35.4 (CH), 31.80 (CH), 31.81 (CH2), 31.1 (CH2), 31.0
(CH2), 29.5 (CH2), 28.1 (CH2), 24.2 (CH2), 21.1 (CH3), 20.9 (CH2), 19.3
(CH3), 18.3 (CH3), 11.8 (CH3); ESI MS, m/z: 517 (MNaþ, 100%), 1011
[(2MþNa)þ, 10%]; HRMS (ESI): m/z calcd for C32H46O2SNa: 517.3116;
found 517.3107.
a
4.2. Synthesis of 3b-phenylsulfanylcholest-5-ene (1a)
d
Cholesteryl p-tosylate (443 mg; 1 mmol) was dissolved in di-
oxane (25 mL), and thiophenol (1.1 g; 10 mmol) was added. The
reaction mixture was refluxed under argon for 4 h and, after
cooling, poured into a 1 M NaOH (200 mL) solution. The reaction
product was exhaustively extracted with benzene (3ꢃ100 mL), the
combined extract was dried over anhydrous Na2SO4, and evapo-
rated in vacuo. The crude product was purified by silica gel column
chromatography affording 283 mg (59% yield) of pure 1a (eluted
with hexane).
Compound 1a; colorless crystals; Rf¼0.39 (CH2Cl2/hexane 1:9);
4.3. Synthesis of 6
(2a)
b-phenylsulfanyl-3a,5a-cyclocholestane
20
mp 78e80 ꢂC (acetone); lit.34 mp 72e74 ꢂC; [
a]
ꢁ37.1 (c 1.0,
D
CHCl3); lit.34
1025 cmꢁ1; 1H NMR,
3H, HeAr), 5.34 (m, 1H, H-6), 3.05 (m, 1H, H-3
[
a
]
D ꢁ39 (c 1.1, CHCl3); IR, nmax: 3062, 1584, 1467, 1091,
(ppm): 7.42 (d, 2H, J¼8.2 Hz, HeAr), 7.28 (m,
), 1.02 (s, 3H, H-19),
d
Cholesteryl p-tosylate (443 mg; 1 mmol) was dissolved in di-
oxane (25 mL), then potassium acetate (590 mg; 6 mmol), and
thiophenol (1.1 g; 10 mmol) were added. The reaction mixture was
refluxed under argon for 6 h and, after cooling, poured into a 1 M
NaOH (200 mL) solution. The reaction product was exhaustively
extracted with benzene (3ꢃ100 mL), the combined extract was
dried with anhydrous Na2SO4, and evaporated in vacuo. The residue
was subjected to silica gel column chromatography. Compounds 2a
(239 mg; 50%) and 1a (43 mg; 9%) were consecutively eluted with
a
0.95 (d, 3H, J¼6.4 Hz, H-21), 0.91 (d, 3H, J¼6.6 Hz, H-26 or H-27),
0.90 (d, 3H, J¼6.7 Hz, H-26 or H-27), 0.71 (s, 3H, H-18); 13C NMR
(ppm), d: 141.6 (C),134.9 (C),131.7 (CH),128.7 (CH),126.6 (CH),121.1
(CH), 56.7 (CH), 56.2 (CH), 50.3 (CH), 47.3 (CH), 42.3 (C), 39.8 (CH2),
39.63 (CH2), 39.62 (CH2), 39.5 (CH2), 36.8 (C), 36.2 (CH2), 35.8 (CH),
31.83 (CH2), 31.80 (CH), 29.5 (CH2), 28.2 (CH2), 28.0 (CH), 24.2 (CH2),
23.8 (CH2), 22.8 (CH3), 22.6 (CH3), 20.9 (CH2), 19.3 (CH3), 18.7 (CH3),
11.8 (CH3); ESI MS, m/z: 501 (MNaþ, 1%); elemental analysis calcd
(%) for C33H50S: C 82.78, H 10.53, S 6.70; found: C 82.49, H 10.56, S
6.72.
hexane.
20
Compound 2a; colorless oil; Rf¼0.40 (CH2Cl2/hexane 1:9); [
a]
D
ꢁ3.2 (c 1.0, CHCl3); lit.34
[
a
]
D þ34 (c 1.1, CHCl3); IR, nmax: 3062, 1584,
1H NMR,
(ppm): 7.38 (d, 2H, J¼8.0 Hz,
),
1468, 1089, 1025 cmꢁ1
;
d
4.2.1. Other sterol thioethers (obtained as products of electrochemical
reactions)
HeAr), 7.24 (m, 3H, HeAr), 2.92 (dd,1H, J1¼3.7 Hz, J2¼2.3 Hz, H-6
a
1.10 (s, 3H, H-19), 0.93 (d, 3H, J¼6.5 Hz, H-21), 0.883 (d, 3H,
J¼6.6 Hz, H-26 or H-27), 0.878 (d, 3H, J¼6.6 Hz, H-26 or H-27), 0.77
(s, 3H, H-18), 0.68 (dd, 1H, J1¼5.2 Hz, J2¼4.2 Hz, H-4a), 0.42 (dd, 1H,
4.2.1.1. 3b-p-Tolylsulfanylcholest-5-ene (1b). Colorless crystals;
20
Rf¼0.34 (CH2Cl2/hexane 1:9); mp 77e78 ꢂC (acetone); [
a
]
ꢁ23.5
;
1DH NMR,
J1¼8.0 Hz, J2¼5.2 Hz, H-4b); 13C NMR,
d: 137.2 (C), 132.1 (CH), 128.7
(c 1.0, CHCl3); IR, nmax: 1492, 1467, 1092, 1019 cmꢁ1
(CH), 126.5 (CH), 56.4 (CH), 56.0 (CH), 54.4 (CH), 47.9 (CH), 43.2
(C), 42.8 (C), 40.2 (CH2), 39.5 (CH2), 36.9 (C), 36.2 (CH2), 35.8 (CH),
35.5 (CH2), 33.6 (CH2), 30.6 (CH), 28.6 (CH), 28.3 (CH2), 28.0 (CH),
25.3 (CH2), 24.2 (CH2), 23.9 (CH2), 22.8 (CH3), 22.7 (CH2), 22.6 (CH3),
20.1 (CH3), 18.7 (CH3), 14.3 (CH2), 12.2 (CH3); EIMS, m/z: 478 (Mþ,
2%), 369 [(MꢁCH3C6H4S)þ, 100%]; elemental analysis calcd (%) for
C33H50S: C 82.78, H 10.53, S 6.70; found: C 82.51, H 10.57, S 6.71.
d
(ppm): 7.32 (d, 2H, J¼8.0 Hz, HeAr), 7.11 (d, 2H, J¼8.0 Hz, HeAr),
5.31 (m, 1H, H-6), 2.95 (m, 1H, H-3 ), 2.34 (s, 3H, H-Ar-CH3), 0.99 (s,
a
3H, H-19), 0.93 (d, 3H, J¼6.5 Hz, H-21), 0.883 (d, 3H, J¼6.6 Hz, H-26
or H-27), 0.879 (d, 3H, J¼6.6 Hz, H-26 or H-27), 0.68 (s, 3H, H-18);
13C NMR (ppm),
d: 141.8 (C), 136.9 (C), 132.6 (CH), 130.9 (C), 129.5
(CH), 121.0 (CH), 56.8 (CH), 56.2 (CH), 50.3 (CH), 47.8 (CH), 42.3 (C),
39.8 (CH2), 39.7 (CH2), 39.6 (CH2), 39.5 (CH2), 36.9 (C), 36.2 (CH2),
35.8 (CH), 31.9 (CH2), 31.8 (CH), 29.6 (CH2), 28.2 (CH2), 28.0 (CH),
24.3 (CH2), 23.8 (CH2), 22.8 (CH3), 22.6 (CH3), 21.1 (CH3), 20.9 (CH2),
19.3 (CH3), 18.7 (CH3), 11.9 (CH3); EIMS, m/z: 492 (Mþ, 15%), 369
[(Mꢁp-CH3C6H4S)þ, 100%]; HRMS (EI): m/z calcd for C34H52S:
492.3790; found 492.3773.
4.3.1. Analogous syntheses
4.3.1.1. 6
b-p-Tolylsulfanyl-3a,5a-cyclocholestane (2b). Colorless
oil; Rf¼0.35 (CH2Cl2/hexane 1:9); [
a
]
20 ꢁ10.5 (c 1.0, CHCl3); IR, nmax
:
D
3063, 1492, 1468, 1089, 1017, 812 cmꢁ1
;
1H NMR,
d
(ppm): 7.29 (d,
2H, J¼8.0 Hz, HeAr), 7.09 (d, 2H, J¼8.0 Hz, HeAr), 2.82 (dd, 1H,
4.2.1.2. 3
b
-p-Tolylsulfanyl-25R-spirost-5-ene
(20). Colorless
J1¼3.7 Hz, J2¼2.3 Hz, H-6
a
), 2.33 (s, 3H, H-Ar-CH3),1.10 (s, 3H, H-19),
crystals; Rf¼0.46 (AcOEt/hexane 5:95); mp 185e186 ꢂC (hexane);
0.93 (d, 3H, J¼6.5 Hz, H-21), 0.880 (d, 3H, J¼6.6 Hz, H-26 or H-27),
0.876 (d, 3H, J¼6.6 Hz, H-26 or H-27), 0.78 (s, 3H, H-18), 0.67 (dd,
1H, J1¼5.2 Hz, J2¼4.2 Hz, H-4a), 0.42 (dd, 1H, J1¼8.0 Hz, J2¼5.2 Hz,
[
d
a
]
20 ꢁ84.8 (c 0.5, CHCl3); IR, nmax: 1049, 1007, 812 cmꢁ1; 1H NMR,
D
(ppm): 7.32 (d, 2H, J¼8.1 Hz, HeAr), 7.11 (d, 2H, J¼8.1 Hz, HeAr),
5.30 (d, 1H, J¼4.5 Hz, H-6), 4.42 (m, 1H, H-16), 3.48 (m, 1H, H-26a),
3.39 (t, 1H, J¼10.8 Hz, H-26b), 2.94 (m, 1H, H-3 ), 2.34 (s, 3H,
H-4b); 13C NMR,
d (ppm): 136.8 (C),133.4 (C),133.0 (CH),129.5 (CH),
a
56.3 (CH), 56.0 (CH), 55.0 (CH), 47.9 (CH), 43.2 (C), 42.8 (C), 40.2
(CH2), 39.5 (CH2), 36.9 (C), 36.2 (CH2), 35.8 (CH), 35.4 (CH2), 33.6
(CH2), 30.5 (CH), 28.5 (CH), 28.3 (CH2), 28.0 (CH), 25.3 (CH2), 24.2
HeAreCH3), 1.01 (s, 3H, H-19), 0.98 (d, 3H, J¼7.0 Hz, H-21), 0.80 (d,
3H, J¼6.8 Hz, H-27), 0.79 (s, 3H, H-18); 13C NMR (ppm),
d: 141.8 (C),

8912
A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
(CH2), 23.8 (CH2), 22.8 (CH3), 22.7 (CH2), 22.6 (CH3), 21.1 (CH3), 20.1
(CH3), 18.7 (CH3), 14.3 (CH2), 12.2 (CH3); EIMS, m/z: 492 (Mþ, 4%),
369 [(Mꢁp-CH3C6H4S)þ, 100%]; elemental analysis calcd (%) for
C34H52S: C 82.86, H 10.63, S 6.51; found: C 82.57, H 10.66, S 6.53.
(10,20:30,40-di-O-isopropylidene- -galactopyranos-60-yl)-cholest-
a-D
5-ene (4; 117 mg, 52%), followed by cholesterol (6; 10 mg, 7%)
eluted with hexaneeethyl acetate (9:1).
4.4.1. 3b a-D
-O-(10,20:30,40-Di-O-isopropylidene- -galactopyranos-60-
yl)-cholest-5-ene (4).35 Colorless crystals; Rf¼0.35 (AcOEt/hexane
4.3.1.2. 6
b-p-Tolylsulfanyl-3a,5a-cyclo-25R-spirostane
1:9); mp 128e131 ꢂC (hexane); [
a
]
20 ꢁ63.7 (c 1.0, CHCl3); IR, nmax
:
(17). Colorless crystals; Rf¼0.49 (AcOEt/hexane 5:95); mp
D
20
118e121 ꢂC (hexane); [
a
]
ꢁ86.6 (c 1.0, CHCl3); IR, nmax: 3063,
1070 cmꢁ1; 1H NMR,
d
(ppm): 5.53 (d, 1H, J¼5.0 Hz, H-10), 5.34 (m,
D
1492, 1456, 1096, 1049, 898, 813 cmꢁ1
;
1H NMR,
d (ppm): 7.29 (d,
1H, H-6), 4.60 (dd, 1H, J1¼7.9 Hz, J2¼2.3 Hz, H-30), 4.30 (dd, 1H,
J1¼5.3 Hz, J2¼2.3 Hz, H-20), 4.28 (dd, 1H, J1¼8.1 Hz, J2¼1.8 Hz, H-40),
3.92 (dt, 1H, J1¼6.3 Hz, J2¼1.7 Hz, H-50), 3.68 (dd, 1H, J1¼10.1 Hz,
J2¼6.3 Hz, H-60a), 3.62 (dd, 1H, J1¼10.1 Hz, J2¼6.5 Hz, H-60b), 3.21
2H, J¼8.1 Hz, HeAr), 7.08 (d, 2H, J¼8.1 Hz, HeAr), 4.39 (m, 1H, H-
16), 3.48 (m, 1H, H-26a), 3.37 (t, 1H, J¼10.9 Hz, H-26b), 2.80 (dd, 1H,
J1¼3.6 Hz, J2¼2.4 Hz, H-6
a), 2.33 (s, 3H, H-Ar-CH3), 1.13 (s, 3H, H-
19), 0.99 (d, 3H, J¼7.0 Hz, H-21), 0.90 (s, 3H, H-18), 0.80 (d, 3H,
J¼6.4 Hz, H-27), 0.69 (dd, 1H, J1¼5.2 Hz, J2¼4.3 Hz, H-4a), 0.47 (dd,
(m, 1H, H-3a), 1.54 (s, 3H, H-isopropylidene), 1.45 (s, 3H, H-iso-
propylidene), 1.35 (s, 3H, Heisopropylidene), 1.33 (s, 3H,
Heisopropylidene), 1.00 (s, 3H, H-19), 0.92 (d, 3H, J¼6.6 Hz, H-21),
0.870 (d, 3H, J¼6.6 Hz, H-26 or H-27), 0.866 (d, 3H, J¼6.6 Hz, H-26
1H, J1¼8.0 Hz, J2¼5.2 Hz, H-4b); 13C NMR,
d (ppm): 137.1 (C), 133.6
(CH), 132.9 (C), 129.6 (CH), 109.3 (C), 80.8 (CH), 66.9 (CH2), 62.3
(CH), 55.8 (CH), 55.1 (CH), 47.9 (CH), 43.3 (C), 41.7 (CH), 40.8 (C),
40.2 (CH2), 36.7 (C), 35.2 (CH2), 33.6 (CH2), 31.8 (CH2), 31.4 (CH2),
30.3 (CH), 30.0 (CH), 28.8 (CH2), 28.6 (CH), 25.3 (CH2), 22.5 (CH2),
21.1 (CH3), 20.2 (CH3), 17.1 (CH3), 16.7 (CH3), 14.5 (CH3), 14.4 (CH2);
EIMS, m/z: 520 (Mþ, 21%), 397 [(Mꢁp-CH3C6H4S)þ, 100%]; HRMS
(EI): m/z calcd for C34H48O2S: 520.3375; found 520.3393.
or H-27), 0.68 (s, 3H, H-18); 13C NMR,
d (ppm): 141.0 (C), 121.4 (CH),
109.0 (C), 108.4 (C), 96.3 (CH), 79.7 (CH), 71.1 (CH), 70.63 (CH), 70.58
(CH), 67.0 (CH), 66.7 (CH2), 56.7 (CH), 56.1 (CH), 50.1 (CH), 42.3 (C),
39.7 (CH2), 39.5 (CH2), 39.0 (CH2), 37.2 (CH2), 36.8 (C), 36.1 (CH2),
35.7 (CH), 31.9 (CH2), 31.8 (CH), 28.4 (CH2), 28.2 (CH2), 27.9 (CH),
26.1 (CH3), 26.0 (CH3), 24.9 (CH3), 24.4 (CH3), 24.2 (CH2), 23.8 (CH2),
22.8 (CH3), 22.5 (CH3), 21.0 (CH2), 19.3 (CH3), 18.7 (CH3), 11.8 (CH3);
EIMS, m/z: 628 [Mþ, <1%], 368 [(Mꢁ1,2:3,4-di-O-isopropylidene-
4.3.1.3. Methyl
Colorless oil; Rf¼0.55 (AcOEt/hexane 1:9); [
CHCl3); IR, nmax: 1731,1492, 1438,1103, 812 cmꢁ1; 1H NMR,
6b-p-tolylsulfanyl-3a,5a-cyclocholanoate (21).
20
a-D
-galactopyranose)þ, 100%]; elemental analysis calcd (%) for
a
]
ꢁ35.3 (c 1.0,
D
d
(ppm):
C39H64O6: C 74.48, H 10.26; found: 74.32, H 10.23.
7.28 (d, 2H, J¼7.9 Hz, HeAr), 7.08 (d, 2H, J¼7.9 Hz, HeAr), 3.67 (s,
3H, Hemethyl ester), 2.82 (m, 1H, H-6), 2.32 (s, 3H, HeAreCH3),
1.12 (s, 3H, H-19), 0.94 (d, 3H, J¼6.5 Hz, H-21), 0.78 (s, 3H, H-18),
0.67 (dd, 1H, J1¼5.4 Hz, J2¼4.5 Hz, H-4a), 0.42 (dd, 1H, J1¼7.8 Hz,
4.4.2. 6
yl)-3 ,5
1:9); [
b a-D
-O-(10,20:30,40-Di-O-isopropylidene- -galactopyranos-60-
a
a
-cyclocholestane (5). White solid; Rf¼0.40 (AcOEt/hexane
a
]
20 ꢁ17.3 (c 0.1, CHCl3); IR, nmax: 1070; 1H NMR,
d (ppm): 5.52
D
J2¼5.4 Hz, H-4b); 13C NMR,
d (ppm): 174.7 (C), 136.7 (C), 133.2 (C),
(d, 1H, J¼5.0 Hz, H-10), 4.60 (dd, 1H, J1¼8.0 Hz, J2¼2.2 Hz, H-30), 4.35
(dd, 1H, J1¼8.1 Hz, J2¼1.7 Hz, H-40), 4.30 (dd, 1H, J1¼5.0 Hz,
J2¼2.3 Hz, H-20), 3.95 (m,1H, H-50), 3.62 (t,1H, J¼8.5 Hz, H-60a), 3.46
(dd, 1H, J1¼8.8 Hz, J2¼5.7 Hz, H-60b), 2.91 (m, 1H, H-6), 1.56 (s, 3H,
Heisopropylidene), 1.45 (s, 3H, Heisopropylidene), 1.35 (s, 6H,
Heisopropylidene), 1.00 (s, 3H, H-19), 0.92 (d, 3H, J¼6.5 Hz, H-21),
0.880 (d, 3H, J¼6.6 Hz, H-26 or H-27), 0.875 (d, 3H, J¼6.6 Hz, H-26
or H-27), 0.72 (s, 3H, H-18), 0.58 (dd, 1H, J1¼4.9 Hz, J2¼4.2 Hz, H-
133.0 (CH), 129.5 (CH), 55.90 (CH), 55.89 (CH), 54.9 (CH), 51.4 (CH3),
47.8 (CH), 43.1 (C), 42.7 (C), 40.1 (CH2), 36.8 (C), 35.4 (CH), 35.3
(CH2), 33.6 (CH2), 31.02 (CH2), 30.96 (CH2), 30.4 (CH), 28.5 (CH), 28.1
(CH2), 25.3 (CH2), 24.2 (CH2), 22.7 (CH2), 21.0 (CH3), 20.1 (CH3), 18.2
(CH3), 14.2 (CH2), 12.2 (CH3); ESI MS, m/z: 1011 [(2MþNa)þ, 5%], 548
[(MNaþMeOH)þ, 30%], 517 (MNaþ, 100%); HRMS (ESI): m/z calcd for
(C32H46O2SNa)þ: 517.3116; found 517.3108.
4a), 0.40 (dd, 1H, J1¼7.8 Hz, J2¼4.9 Hz, H-4b); 13C NMR,
d (ppm):
4.4. Electrolysis of 6b-p-tolylsulfanyl-3a,5a-cyclocholestane
(2b) in the presence of 1,2:3,4-di-O-isopropylidene-D-gal-
actopyranose (3)
108.8 (C), 108.4 (C), 96.3 (CH), 80.7 (CH), 71.0 (CH), 70.9 (CH), 70.5
(CH), 66.8 (CH), 65.9 (CH2), 56.5 (CH), 56.4 (CH), 48.0 (CH), 43.3 (C),
42.8 (C), 40.4 (CH2), 39.6 (CH2), 36.4 (C), 36.2 (CH2), 35.9 (CH), 34.4
(CH2), 33.3 (CH2), 30.2 (CH), 28.3 (CH2), 28.0 (CH), 26.1 (CH3), 26.0
(CH3), 25.1 (CH2), 25.0 (CH3), 24.4 (CH3), 24.2 (CH2), 23.9 (CH2),
22.82 (CH3), 22.79 (CH2), 22.6 (CH3), 22.2 (CH), 19.4 (CH3), 18.7
(CH3), 12.9 (CH2), 12.3 (CH3); ESI MS, m/z: 651 (MNaþ, 100%); HRMS
(ESI): m/z calcd for C39H64O6Naþ: 651.4601; found 651.4614.
6
b
-p-Tolylsulfanyl-3
a
,5
a
-cyclocholestane (2b; 176 mg; 0.36
-galactopyranose (3;
mmol) and 1,2,3:4-di-O-isopropylidene-
D
93 mg; 0.36 mmol) were dissolved in a 0.1 M solution of tetrabu-
tylammonium tetrafluoroborate in dichloromethane (3.5 mL) and
introduced into the anodic compartment together with a 0.3 g of 3A
molecular sieve to eliminate traces of water. The same supporting
electrolyte was placed in the cathodic compartment with an
anionite (1 g, Dowex 2x8, 200e400 mesh, perchlorate form) added
to eliminate chloride ions from forming by the reduction of
dichloromethane. A preparative electrolysis was carried out in
a divided H-cell in which the cathodic and anodic compartments
(3.5 mL of electrolytes each) were separated by a glass frit under
galvanostatic conditions. A direct current 7.5 mA was run for
4000 s. A platinum mesh was used as a cathode and a platinum
plate (2ꢃ1.5 cm) was used as an anode. Ag/0.1 M AgNO3 in an
acetonitrile electrode was used as a reference. When the electrol-
ysis was completed the solvent was removed from the reaction
mixture and products were separated by silica gel column chro-
4.4.3. Other glycoconjugates obtained as products of the electro-
chemical reactions
4.4.3.1. 3b a-D-glucofuranos-
-O-(10,20:50,60-Di-O-cyclohexylidene-
30-yl)-cholest-5-ene (14). Colorless crystals; Rf¼0.53 (AcOEt/hexane
15:85); mp 49e52 ꢂC (hexane); [
a
]
D
20 ꢁ17.4 (c 0.25, CHCl3); IR, nmax
:
1077 cmꢁ1; 1H NMR,
d
(ppm): 5.89 (d, 1H, J¼3.6 Hz, H-10), 5.34 (m,
1H, H-6), 4.46 (d, 1H, J¼3.6 Hz, H-20), 4.30 (m, 1H, H-50), 4.10 (m, 2H,
H-60a, H-40), 4.04 (d, 1H, J¼3.1 Hz, H-30), 3.95 (dd, 1H, J1¼8.4 Hz,
J2¼6.1 Hz, H-60b), 3.36 (m, 1H, H-3
a), 1.01 (s, 3H, H-19), 0.92 (d, 3H,
J¼6.5 Hz, H-21), 0.88 (d, 3H, J¼6.6 Hz, H-26 or H-27), 0.87 (d, 3H,
J¼6.6 Hz, H-26 or H-27), 0.69 (s, 3H, H-18); 13C NMR,
d (ppm): 140.7
(C), 121.8 (CH), 112.4 (C), 109.4 (C), 105.0 (CH), 83.6 (CH), 81.4 (CH),
80.1 (CH), 79.6 (CH), 72.2 (CH), 67.2 (CH2), 56.8 (CH), 56.2 (CH), 50.2
(CH), 42.3 (C), 39.8 (CH2), 39.5 (CH2), 38.9 (CH2), 37.3 (CH2), 36.8 (C),
36.51 (CH2), 36.48 (CH2), 36.2 (CH2), 35.78 (CH), 35.76 (CH2), 34.9
(CH2), 32.0 (CH2), 31.9 (CH), 29.3 (CH2), 28.2 (CH2), 28.0 (CH), 25.2
(CH2), 24.9 (CH2), 24.3 (CH2), 24.1 (CH2), 23.91 (CH2), 23.89 (CH2),
matography. The hexane elution afforded
nylcholest-5-ene (1b; 38 mg; 22%). With the hexaneeethyl acetate
mixture (95:5) -gal-
-O-(10,20:30,40-di-O-isopropylidene-
actopyranos-60-yl)-3
-cyclocholestane (5; 2 mg; 1%) was eluted.
Further elution with hexaneeethyl acetate (93:7) afforded 3 -O-
3b-p-tolylsulfa-
6b
a-D
a,5a
b

A.M. Tomkiel et al. / Tetrahedron 69 (2013) 8904e8913
8913
23.8 (CH2), 23.6 (CH2), 22.8 (CH3), 22.5 (CH3), 21.1 (CH2), 19.4 (CH3),
Development of Eastern Poland 2007e2013 (project No.
POPW.01.03.00-20-034/09-00).
18.7 (CH3), 11.8 (CH3); EIMS, m/z: 708 (Mþ, 1%), 368 [(Mꢁ10,20:50,60-
di-O-cyclohexylidene-D
-glucofuranose)þ, 100%]; elemental analysis
calcd (%) for C45H72O6: C 76.23, H 10.24; found: C 76.17, H 10.28.
Supplementary data
4.4.3.2. 3b a-D-galactopyr-
-O-(10,20:30,40-Di-O-isopropylidene-
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.07.106.
anos-60-yl)-(25R)-spirost-5-ene (18). Colorless crystals; Rf¼0.27
20
(AcOEt/hexane 1:9); mp 179e180 ꢂC (hexane), [
a
]
D
ꢁ92.1 (c 1.0,
CHCl3); IR, nmax: 1456, 1069 cmꢁ1 1H NMR,
; d (ppm): 5.54 (d, 1H,
References and notes
J¼5.0 Hz, H-10), 5.34 (m, 1H, H-6), 4.60 (dd, 1H, J1¼7.9 Hz, J2¼2.3 Hz,
H-30), 4.40 (m, 1H, H-16), 4.30 (dd, 1H, J1¼5.0 Hz, J2¼2.4 Hz, H-20),
4.28 (dd, 1H, J1¼8.1 Hz, J2¼2.1 Hz, H-40), 3.93 (dt, 1H, J1¼6.3 Hz,
J2¼1.6 Hz, H-50), 3.68 (dd, 1H, J1¼10.1 Hz, J2¼6.2 Hz, H-60a), 3.63 (dd,
1H, J1¼10.1 Hz, J2¼6.5 Hz, H-60b), 3.48 (m, 1H, H-26a), 3.38 (t, 1H,
ꢀ
~
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Heisopropylidene), 1.34 (s, 3H, Heisopropylidene), 1.02 (s, 3H, H-
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(C), 108.5 (C), 96.4 (CH), 80.8 (CH), 79.7 (CH), 71.1 (CH), 70.7 (CH),
70.6 (CH), 67.1 (CH), 66.82 (CH2), 66.80 (CH2), 62.1 (CH), 56.5 (CH),
50.1 (CH), 41.6 (CH), 40.3 (C), 39.8 (CH2), 39.0 (CH2), 37.2 (CH2), 37.0
(C), 32.1 (CH2), 31.8 (CH2), 31.44 (CH), 31.39 (CH2), 30.3 (CH), 28.8
(CH2), 28.4 (CH2), 26.1 (CH3), 26.0 (CH3), 24.9 (CH3), 24.4 (CH3), 20.8
(CH2), 19.4 (CH3), 17.1 (CH3), 16.3 (CH3), 14.5 (CH3); ESI MS, m/z: 679
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20
(AcOEt/hexane 2:8); [
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d
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1H, H-6), 4.60 (dd, 1H, J1¼8.0 Hz, J2¼2.4 Hz, H-30), 4.30 (dd, 1H,
J1¼5.1 Hz, J2¼2.4 Hz, H-20), 4.28 (dd, 1H, J1¼8.2 Hz, J2¼1.8 Hz, H-40),
3.94 (dt, 1H, J1¼6.3 Hz, J2¼1.7 Hz, H-50), 3.69 (dd, 1H, J1¼10.1 Hz,
J2¼6.4 Hz, H-60a), 3.67 (s, 3H, Hemethyl ester), 3.63 (dd, 1H,
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J1¼10.1 Hz, J2¼6.4 Hz, H-60b), 3.22 (m, 1H, H-3
a), 1.55 (s, 3H,
Heisopropylidene), 1.46 (s, 3H, Heisopropylidene), 1.36 (s, 3H,
Heisopropylidene), 1.34 (s, 3H, Heisopropylidene), 1.01 (s, 3H, H-
19), 0.94 (d, 3H, J¼6.5 Hz, H-21), 0.70 (s, 3H, H-18); 13C NMR,
d
(ppm): 174.7 (C), 141.2 (C), 121.4 (CH), 109.2 (C), 108.5 (C), 96.5
(CH), 79.8 (CH), 71.3 (CH), 70.9 (CH), 70.8 (CH), 67.2 (CH), 66.9
(CH2), 56.8 (CH), 55.9 (CH), 51.4 (CH3), 50.3 (CH), 42.5 (C), 39.9
(CH2), 39.2 (CH2), 37.3 (CH2), 36.9 (C), 35.4 (CH), 32.00 (CH), 31.98
(CH2), 31.14 (CH2), 31.11 (CH2), 28.5 (CH2), 28.1 (CH2), 26.2 (CH3),
26.1 (CH3), 25.0 (CH3), 24.5 (CH3), 24.3 (CH2), 21.1 (CH2), 19.4 (CH3),
18.4 (CH3), 11.9 (CH3); ESI MS, m/z: 653 (MNaþ, 100%); HRMS (ESI):
m/z calcd for (C37H58O8Na)þ: 653.4029; found 653.4041.
Acknowledgements
33. Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112e122.
34. Shoppee, C. W.; Richards, H. C.; Summers, H. R. J. Chem. Soc. 1956, 4817e4821.
35. This compound was described in our previous paper,19 but the physical and
spectroscopic data were erroneously given therein for the 30,40-mono-O-iso-
propylidene derivative.
Financial support from the Polish National Science Center
(UMO-2011/01/B/ST5/06046) is gratefully acknowledged. The pur-
chase of an X-ray diffractometer was sponsored by the European
Fund for Regional Development as part of the Operational Program