Full Text
Reports of the Academy of Sciences of the USSR
1964. Volume 155, No. 3
CHEMISTRY
V. I. LITVINENKO
CHALCONE GLYCOSIDES OF LICORICE—GLYCYRRHIZA GLABRA L.
(Presented by Academician A. I. Oparin, 2 IX 1963)
In studying the qualitative composition of the flavonoids of licorice, it was established that in the roots and rhizomes these compounds are represented mainly by two classes: flavonones and chalcones. Some of the pigments discovered were isolated by means of column chromatography on a polyamide sorbent (¹).
The subject of the present work was the study of two of them, designated as substances L-7 and L-8. The isolated flavonoids are individual crystalline compounds, the physicochemical properties of which are shown in Tables 1 and 2.
The data presented indicate that substances L-7 and L-8 are chalcone monoglycosides of isoliquiritigenin (2,4,4′-trioxychalcone). From the spectral properties it was found that the sugar substituent is located in flavonoid L-7 at the 4 position, and in flavonoid L-8 at the 4′ position. One of the features of the chalcone derivatives under study is
Table 1
Physicochemical properties of chalcone glycosides and their derivatives
| Properties and qualitative reactions | Isoliquiritin (⁹) | Substance L-8 | Neoisoliquiritin (L-7) | Acetyl derivatives L-7 | Acetyl derivatives L-8 |
|---|---|---|---|---|---|
| M.p., °C | 185—186 | 187—189 | 230—232 | 158—160 | 169—171 |
| Mol. weight | 418.0 | 418.0 | 418.0 | 670.0 | 670.0 |
| Formula | C₂₁H₂₂O₉ | C₂₁H₂₂O₉ | C₂₁H₂₂O₉ | C₃₃H₃₄O₁₅ | C₃₃H₃₄O₁₅ |
| Optical activity | −62.15° (¹⁰) (C 1.07, methanol) | −60.8° (C1 ethanol) | −61.5° (C 0.5, ethanol) | −12.8° (C1, acetone) | −13.5° (C 0.52, acetone) |
| Values of $R_f$ | |||||
| 1. n-Butanol—acetic acid—water (4 : 1 : 2) | 0.52 | 0.52 | 0.56 | — | — |
| 2. 15% acetic acid | 0.31 | 0.31 | 0.37 | — | — |
| Color of spots with alkali | greenish-yellow | greenish-yellow | orange | — | — |
| Cyanidin reaction (²) | positive in water | positive in water | positive in water | negative | negative |
| Reaction in FeCl₃ | brown | brown | brown | negative | negative |
| Reaction with SbCl₅ (³) | orange | orange | orange | negative | negative |
| Aglycone | isoliquiritigenin | isoliquiritigenin | isoliquiritigenin | isoliquiritigenin | isoliquiritigenin |
| Carbohydrate component | D-glucose | D-glucose | D-glucose | D-glucose | D-glucose |
Table 2
Spectral properties of chalcone glycosides and their aglycone
| Solutions and reagents | A. Isoliquiritin (L-8), band 1 | A. Isoliquiritin (L-8), band 2 | A. Isoliquiritin (L-8), Δλ, ½ | B. Neoisoliquiritin (L-7), band 1 | B. Neoisoliquiritin (L-7), band 2 | B. Neoisoliquiritin (L-7), Δλ, ½ | C. Isoliquiritigenin, band 1 | C. Isoliquiritigenin, band 2 | C. Isoliquiritigenin, Δλ, ½ | Position of free phenolic hydroxyls, A | Position of free phenolic hydroxyls, B | Position of free phenolic hydroxyls, C |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solution in absolute ethanol, 0.5·10⁻⁵ molar | 360 | 260 | — | 370 | 240 | — | 370 | 255 | — | — | — | — |
| Ethanolic solution + sodium acetate | 325 375 |
260 | +15 0 |
295 370 |
250 | 0 +10 |
380 | +10 — |
4+ | 4— | 4+ | |
| Ethanolic solution + sodium ethylate | 315 395 |
225 280 |
+35 +20 |
340 445 |
252 280 |
+75 +40 |
310 350 430 |
252 | +60 −2 |
4′— | 4′+ | 4′+ |
| Ethanolic solution + aluminum chloride | 315 365 |
240 | +5 −20 |
315 375 420 |
250 | +50 +10 |
315 360 |
230 | −10 −25 |
2+ | 2+ | 2+ |
| Ethanolic solution of acetyl derivatives | 320 | 233 | — | 310 | 226 | — | 310 | 225 | — | — | — | — |
Table 3
Comparison of molecular rotations of chalcone glycosides
| Glycosides | \([M]_D\) of glycosides | \([M]_D\) of acetyl derivatives |
|---|---|---|
| Isoliquiritin (L-8) | −254.0° | −86.0° |
| Neoisoliquiritin (L-7) | −257.0° | −90.5° |
| Phenyl-β-D-glucopyranoside | −182.0° | −123.0° |
| Phenyl-α-D-glucopyranoside | +402.0° | +688.0° |
a hypsochromic shift, observed upon addition of aluminum chloride to alcoholic solutions of glycoside L-8 and isoliquiritigenin, instead of the expected bathochromic shift (⁴). This is apparently due to the influence of the free hydroxyl group in position 4, conjugated with the carbonyl group.
The carbohydrate component, according to its physicochemical properties (m.p. 145–147°, \([\alpha]_D^{20} +51.5^\circ\) in water, etc.), was characterized as D-glucose.
According to enzymatic hydrolysis data and by the method of molecular-rotation differences (⁵, ⁶), it was determined, as shown in Table 3, that D-glucose is linked to the aglycone in both glycosides by a β-bond.
The geometrical isomerism of the chalcones was investigated by spectral methods; the results of these studies are given in Table 4.
From the data obtained it is evident that the absorption maxima of band 1 of the chalcone derivatives are considerably more intense than the maxima of band 2, which is characteristic of trans-chalcones (⁷, ⁸). Irradiation of the oxy derivatives of chalcones with ultraviolet light did not lead to the formation of an equilibrium mixture of cis- and trans-isomers. To confirm the geometrical isomerism of the glycosides under investigation and of isoliquiritigenin, their acetyl derivatives were synthesized and studied; after irradiation with ultraviolet light for 15 min at a distance of 20 cm from the radiation source (PRK-4), these form a mixture of isomers. This is clearly shown in Table 4 by the change in intensity of the absorption maxima in bands 1 and 2.
Table 4
Spectroscopic study of the geometrical isomerism of chalcone derivatives
(maxima (λ, mµ) and absorption intensity)
| Compounds | Before irradiation with UV light, band 1: λ | Before irradiation with UV light, band 1: ε | Before irradiation with UV light, band 2: λ | Before irradiation with UV light, band 2: ε | After 15-min irradiation, band 1: λ | After 15-min irradiation, band 1: ε | After 15-min irradiation, band 2: λ | After 15-min irradiation, band 2: ε |
|---|---|---|---|---|---|---|---|---|
| Isoliquiritin (L-8) | 360 | 35990 | 260 | 10000 | 360 | 35990 | 260 | 10000 |
| Acetyl derivative of L-8 | 320 | 22000 | 233 | 20500 | 320 | 14500 | 233 | 12500 |
| Neoisoliquiritin (L-7) | 370 | 27540 | 240 | 10230 | 370 | 27540 | 240 | 10230 |
| Acetyl derivative of L-7 | 310 | 18620 | 266 | 19940 | 310 | 12200 | 226 | 10700 |
| Isoliquiritigenin | 370 | 33910 | 255 | 3390 | 370 | 13910 | 255 | 3390 |
| Acetyl derivative of isoliquiritigenin | 310 | 26300 | 225 | 19950 | 310 | 15850 | 225 | 18620 |
On the basis of the data obtained, the following structural formula may be proposed for the chalcone glycosides studied: in L-8, \(R — H\) and \(R' —\) a glucosyl residue, whereas in L-7 \(R —\) a glucosyl residue and \(R' — H\).
Therefore the flavonoid L-8 should be designated as trans-isoliquiritigenin-4′-\(\beta\)-D-glucopyranoside, identified with isoliquiritin \((^9)\), and the flavonoid L-7 as trans-isoliquiritigenin-4-\(\beta\)-D-glucopyranoside.
\[ \mathrm{RO{-}C_6H_3(OH){-}CO{-}CH{=}CH{-}C_6H_4{-}OR'} \]
For the latter we propose the trivial name — neoisoliquiritin.
Kharkov Scientific-Research
Chemical-Pharmaceutical Institute
Received
30 VIII 1963
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