Beilstein J. Org. Chem. 2015, 11, 162–168.
2273) under galvanostatic conditions using a current that was Typical electrochemical experiment. Anodic oxidation of
equal in a typical experiment to 7.5 mA and a reaction time of 6β-phenyloxy-3α,5α-cyclocholestane (6f) in the presence of
4000 s. The current applied was the maximum current available 1,2:3,4-di-O-isopropylidene-D-galactopyranose (7):
for the electrolysis set-up being used (power supply and ohmic 6β-Phenyloxy-3α,5α-cyclocholestane (138 mg, 0.30 mmol) and
resistance). During the electrolysis the potential of the anode 1,2:3,4-di-O-isopropylidene-D-galactopyranose (94 mg,
was monitored and the process was stopped when the potential 0.36 mmol) were dissolved in a 0.1 M solution of tetrabutylam-
reached the value of +2.3 V vs Ag/0.1 M AgNO3 to avoid the monium tetrafluoroborate in dichloromethane (3.5 mL) and
occurrence of undesired oxidation processes. The reactions introduced into the anodic compartment together with 0.5 g 3 Å
were also monitored by TLC and stopped when no further molecular sieves to eliminate traces of water. The same
increase in the concentration of the glycosylation products was supporting electrolyte was placed in the cathodic compartment
observed. A divided H-cell was used in which the cathodic and with an anionite (2 g, Dowex 2 × 8, 200–400 mesh, perchlorate
anodic compartments (3.5 mL of electrolyte each) were sep- form) added. Preparative electrolysis was carried out in a
arated by a glass frit. In all measurements, 0.1 M solution of divided H-cell in which the cathodic and anodic compartments
tetrabutylammonium tetrafluoroborate (TBABF4) from Aldrich (3.5 mL of electrolytes each) were separated by a glass
in dichloromethane was used as a supporting electrolyte. The frit under galvanostatic conditions. A direct current 7.5 mA
steroid (0.30 mmol) and sugar (0.36 mmol) substrates were was run for 4000 s. A platinum mesh was used as a cathode and
introduced into the anodic compartment together with 0.3 g of a platinum plate (2 × 1.5 cm) was used as an anode.
3 Å molecular sieves added to eliminate traces of water, Ag/0.1 M AgNO3 in an acetonitrile electrode was used as a
whereas anionite (1.5–2 g, Dowex 2 × 8, 200–400 mesh, per- reference. When the electrolysis was completed, the solvent was
chlorate form) was placed in the cathodic compartment to elimi- removed from the reaction mixture and the products were sep-
nate chloride ions that are formed by the reduction of dichloro- arated by silica gel column chromatography. The hexane elution
methane. The solutions in both compartments were stirred afforded diene 13 (1 mg, 1%) and cholesteryl chloride 14
during electrolysis and, additionally, a continuous flow of argon (1 mg, 1%). With the hexane/ethyl acetate mixture (96:4),
was applied in the anodic compartment. A platinum mesh was cholesteryl phenyl ether 12f (31 mg, 22%) was eluted. Further
used as a cathode and a platinum plate (2 × 1.5 cm) was used as elution with hexane/ethyl acetate (93:7) afforded 3β-O-
an anode. All measurements were performed at 25 °C.
(1’,2’:3’,4’-di-O-isopropylidene-α-D-galactopyranos-6’-yl)-
cholest-5-ene (11, 108 mg, 58%), followed by cholesterol 1
The sugar (1,2:3,4-di-O-isopropylidene-α-D-galactopyranose; (5 mg, 4%) eluted with hexane/ethyl acetate (9:1).
7) [9] and steroidal substrates, 3α,5α-cyclocholestan-6β-ol
(i-cholesterol; 6a) [10], 6β-methoxy-3α,5α-cyclocholestane (6b) Glycosylation product 11 was described in our previous paper
[11], and 6β-ethoxy-3α,5α-cyclocholestane (6c) [12], were [4]. Also, other products of the electrochemical reactions (com-
prepared according to known procedures.
pounds 2, 13, 14, and 15) were described in our previous papers
[1-5]. The isomerization products, i.e., 3β-cholesteryl ethers
Melting points were determined on a Toledo Mettler-MP70 12b [13], 12c [14], 12e [15], 12f [14], 12g [5], and 12h [16], are
apparatus. 1H and 13C NMR (400 and 100 MHz, respectively) known compounds, except for 12d which was obtained during
spectra were recorded on a Bruker Avance II spectrometer in electrochemical reaction of 3α,5α-cyclocholestan-6β-yl iso-
selected signals in the 1H NMR spectra are reported in experimental data.
the ‘prime’ index). Infrared spectra were recorded on a Nicolet
Supporting Information
series II Magna-IR 550 FTIR spectrometer in chloroform solu-
tions. Mass spectra were recorded at 70 eV with a time-of-flight
Supporting Information File 1
(TOF) AMD-604 spectrometer with electrospray ionization
(ESI) or AutoSpec Premier (Waters) (EI).
Experimental section including 1H, 13C NMR, and mass
spectra for all new compounds.
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
chromatography performed on a 70–230 mesh silica gel (J. T.
Baker).
Acknowledgements
Financial support from the Polish National Science Centre
(UMO-2011/01/B/ST5/06046) is gratefully acknowledged.
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