- Email: [email protected]
Synthesis of flavone-7-O-glucoside by an electrochemical method
ELSEVIER
Journal of Electroanalytical Chemistry 379 (1994) 517-518
Short communication
Synthesis of flavone-7-0-glucoside
by an electrochemical
method
N. Sulochana a,*, Prabavathi Nagarajan b a Department of Chemistry, Regional Engineering College, Tiruchirapalli-620 015, TN, India b Department of Chemistry, Bishop Heber College, Tiruchirapalli-620 015, TN, India
Received 4 March 1994; in revised form 11April 1994
Keywords:
Electrosynthesis;
Flavone-7-0-glucoside
1. Introduction
The electrochemical preparation of flavone-7-O-glucoside from its aglycone and a-acetobromoglucose under mild electrolytic conditions in 2% NaOH solution with tetrabutylammonium bromide (TBAB) as the supporting electrolyte is described. The preparation of glycosides of flavonoid compounds by chemical methods has been described in literature [l-4]. However, the electro-organic synthesis of flavone-7-0-glucoside has not been reported so far. In the present communication we report a successful attempt to prepare the glucoside of 7-hydroxyflavone by a novel electrochemical method using cu-acetobromoglucose in 2% NaOH solution with TBAB as the supporting electrolyte. The mechanism for the heterolysis of glucosyl derivatives with an anomeric leaving group (Glu-X) (Scheme 1) has been proposed in our previous communications [5,61. We claim the generality of this reaction with respect to other monohydroxy flavones, and the work is in progress in our laboratory.
Glu-Br
3
Glu-B;
2
Glt z
All chemicals used were of AnalaR grade. 7-Hydroxyflavone was obtained from Bio-organics, India, and recrystallized from methanol (mp 244°C). An anodic cyclic voltammetric study was carried out using a three-electrode cell configuration with a-acetobromoglucose (3 x lop3 M) in 2% NaOH solution and 0.1 M TBAB as the supporting electrolyte. Pt wire was used as the anode, a Pt foil of dimensions 3 cm x 3 cm was
author.
0022-0728/94/$07.00
0 1994 Elsevier Science S.A. All rights reserved
SSDI 0022-0728(94)3499-S
Glu-OR
4
I;I
FH,OAc
Glu-Br =
2. Experimental
* Corresponding
used as the counter-electrode and a saturated calomel electrode (SCE) was used as the reference electrode. The Pt electrodes were treated with 5% HNO, to maintain a clear reproducible surface, washed with dilute liquid soap solution, washed thoroughly with triple-distilled water and dried with acetone to remove adhering moisture before being introduced into the cell. An EG & G PAR 273 potentiostat-galvanostat equipped with an IBM PS/2 computer, a HIPLOT DMP-40 series digital plotter and EG & G M 270 software were used to acquire the data. Solutions were
Br (JH ,OAc Glu+=
AC;)
+ CH ,OAc
Scheme 1.
518
N. Sulochana, P. Nagarajan /Journal
of Electroanalytical Chemistry 379 (1994) 517-518
deoxygenated by purging with nitrogen gas for 15 min prior to measurements, and a stream of N, was passed over the solution during the measurements. UV spectra were recorded with a Jasco UVIDEC-430 B double-beam spectrophotometer and an RC-150 M desktop recorder. IR spectra were recorded with a PerkinElmer 1430 ratio recording IR spectrophotometer. The cyclic voltammogram of a-acetobromoglucose shows a well-defined anodic single irreversible peak with no complementary cathodic peak in the reverse scan. The positive shift of peak potential with sweep rate, the absence of cathodic waves on the reverse scan and fairly constant 1,/v ‘I2 confirms that the oxidation process is diffusion controlled and irreversible. The cyclic voltammogram of the aglycone under identical conditions and in the potential range of interest shows no characteristic peak. Controlled-potential electrolysis was carried out at this peak potential (787 mV/SCE) in a divided cell with Pt electrodes. Equimolar quantities of (Yacetobromoglucose and 7-hydroxyflavone in 2% NaOH (50 ml) with TBAB supporting electrolyte formed the anolyte solution and the catholyte solution contained solvent and supporting electrolyte. The temperature was maintained at 10°C with an ice bath. After electrolysis, the anolyte solution was poured into ice-cold water, neutralized to pH 6 and extracted with ether to recover the aglycone and then with ethyl acetate. The ethyl acetate layer was evaporated and the residue (mp 183°C) was dissolved in minimum amount of methanol and deacetylation was carried out with a trace of sodium methoxide in methanol at room
temperature. The product was recrystallized from 50% aqueous methanol (yellow needles, mp 260°C [7], yield 84.7%, current efficiency 76.0%). Elemental analysis: found, 65.67% C and 4.23% H; calculated 63% C and 5% H. Az$‘H 250,318 nm; broad intense IR bands [9] in the range 1100-1050 cm-’ and 3500-344 cm-‘.
Acknowledgements
PN is grateful to the management and the principal of Bishop Heber College for their encouragement, to UGC, New Delhi, for the award of Research Fellowship and to Dr. M. Palaniyandavar and Miss S. Usha, Bharathidasan University, Tiruchirapalli, for their kind permission to carry out cyclic voltammetric studies.
References [l] [2] [3] [4] [5] [61 [7] [8]
[9]
C.H. Ice and S.H. Wender, J. Am. Chem. Sot., 74 (1952) 4606. L. Jurd, J. Org. Chem., 27 (1962) 1294. L. Farkas and B. Vermes, J. Indian Chem. Sot., 55 (1978) 1192. D. Costar, S.A., Le Andros, T. Francois and K. Michel, Chem. Abstr., 31 (1990) 207. N. Sulochana and N. Prabavathi, Indian J. Chem., 32B (1993) 599. N. Prabavathi, Ph.D. Thesis, 1993, submitted to the Bharathidasan University, Tiruchirapalli. B. Ronald, Chem. Abstr., 57 (1963) 13730. T.J. Mabry, K.R., Markham and M.B. Thomas, The Systematic Identification of Flavonoids, Springer-Verlag, New York, 1970, p. 45. H. Wagner in J.B. Pridham (ed.), Methods in Polyphenol Chemistry, Pergamon, Oxford, 1963, p. 37.
Journal of Electroanalytical Chemistry 379 (1994) 517-518
Short communication
Synthesis of flavone-7-0-glucoside
by an electrochemical
method
N. Sulochana a,*, Prabavathi Nagarajan b a Department of Chemistry, Regional Engineering College, Tiruchirapalli-620 015, TN, India b Department of Chemistry, Bishop Heber College, Tiruchirapalli-620 015, TN, India
Received 4 March 1994; in revised form 11April 1994
Keywords:
Electrosynthesis;
Flavone-7-0-glucoside
1. Introduction
The electrochemical preparation of flavone-7-O-glucoside from its aglycone and a-acetobromoglucose under mild electrolytic conditions in 2% NaOH solution with tetrabutylammonium bromide (TBAB) as the supporting electrolyte is described. The preparation of glycosides of flavonoid compounds by chemical methods has been described in literature [l-4]. However, the electro-organic synthesis of flavone-7-0-glucoside has not been reported so far. In the present communication we report a successful attempt to prepare the glucoside of 7-hydroxyflavone by a novel electrochemical method using cu-acetobromoglucose in 2% NaOH solution with TBAB as the supporting electrolyte. The mechanism for the heterolysis of glucosyl derivatives with an anomeric leaving group (Glu-X) (Scheme 1) has been proposed in our previous communications [5,61. We claim the generality of this reaction with respect to other monohydroxy flavones, and the work is in progress in our laboratory.
Glu-Br
3
Glu-B;
2
Glt z
All chemicals used were of AnalaR grade. 7-Hydroxyflavone was obtained from Bio-organics, India, and recrystallized from methanol (mp 244°C). An anodic cyclic voltammetric study was carried out using a three-electrode cell configuration with a-acetobromoglucose (3 x lop3 M) in 2% NaOH solution and 0.1 M TBAB as the supporting electrolyte. Pt wire was used as the anode, a Pt foil of dimensions 3 cm x 3 cm was
author.
0022-0728/94/$07.00
0 1994 Elsevier Science S.A. All rights reserved
SSDI 0022-0728(94)3499-S
Glu-OR
4
I;I
FH,OAc
Glu-Br =
2. Experimental
* Corresponding
used as the counter-electrode and a saturated calomel electrode (SCE) was used as the reference electrode. The Pt electrodes were treated with 5% HNO, to maintain a clear reproducible surface, washed with dilute liquid soap solution, washed thoroughly with triple-distilled water and dried with acetone to remove adhering moisture before being introduced into the cell. An EG & G PAR 273 potentiostat-galvanostat equipped with an IBM PS/2 computer, a HIPLOT DMP-40 series digital plotter and EG & G M 270 software were used to acquire the data. Solutions were
Br (JH ,OAc Glu+=
AC;)
+ CH ,OAc
Scheme 1.
518
N. Sulochana, P. Nagarajan /Journal
of Electroanalytical Chemistry 379 (1994) 517-518
deoxygenated by purging with nitrogen gas for 15 min prior to measurements, and a stream of N, was passed over the solution during the measurements. UV spectra were recorded with a Jasco UVIDEC-430 B double-beam spectrophotometer and an RC-150 M desktop recorder. IR spectra were recorded with a PerkinElmer 1430 ratio recording IR spectrophotometer. The cyclic voltammogram of a-acetobromoglucose shows a well-defined anodic single irreversible peak with no complementary cathodic peak in the reverse scan. The positive shift of peak potential with sweep rate, the absence of cathodic waves on the reverse scan and fairly constant 1,/v ‘I2 confirms that the oxidation process is diffusion controlled and irreversible. The cyclic voltammogram of the aglycone under identical conditions and in the potential range of interest shows no characteristic peak. Controlled-potential electrolysis was carried out at this peak potential (787 mV/SCE) in a divided cell with Pt electrodes. Equimolar quantities of (Yacetobromoglucose and 7-hydroxyflavone in 2% NaOH (50 ml) with TBAB supporting electrolyte formed the anolyte solution and the catholyte solution contained solvent and supporting electrolyte. The temperature was maintained at 10°C with an ice bath. After electrolysis, the anolyte solution was poured into ice-cold water, neutralized to pH 6 and extracted with ether to recover the aglycone and then with ethyl acetate. The ethyl acetate layer was evaporated and the residue (mp 183°C) was dissolved in minimum amount of methanol and deacetylation was carried out with a trace of sodium methoxide in methanol at room
temperature. The product was recrystallized from 50% aqueous methanol (yellow needles, mp 260°C [7], yield 84.7%, current efficiency 76.0%). Elemental analysis: found, 65.67% C and 4.23% H; calculated 63% C and 5% H. Az$‘H 250,318 nm; broad intense IR bands [9] in the range 1100-1050 cm-’ and 3500-344 cm-‘.
Acknowledgements
PN is grateful to the management and the principal of Bishop Heber College for their encouragement, to UGC, New Delhi, for the award of Research Fellowship and to Dr. M. Palaniyandavar and Miss S. Usha, Bharathidasan University, Tiruchirapalli, for their kind permission to carry out cyclic voltammetric studies.
References [l] [2] [3] [4] [5] [61 [7] [8]
[9]
C.H. Ice and S.H. Wender, J. Am. Chem. Sot., 74 (1952) 4606. L. Jurd, J. Org. Chem., 27 (1962) 1294. L. Farkas and B. Vermes, J. Indian Chem. Sot., 55 (1978) 1192. D. Costar, S.A., Le Andros, T. Francois and K. Michel, Chem. Abstr., 31 (1990) 207. N. Sulochana and N. Prabavathi, Indian J. Chem., 32B (1993) 599. N. Prabavathi, Ph.D. Thesis, 1993, submitted to the Bharathidasan University, Tiruchirapalli. B. Ronald, Chem. Abstr., 57 (1963) 13730. T.J. Mabry, K.R., Markham and M.B. Thomas, The Systematic Identification of Flavonoids, Springer-Verlag, New York, 1970, p. 45. H. Wagner in J.B. Pridham (ed.), Methods in Polyphenol Chemistry, Pergamon, Oxford, 1963, p. 37.