Isoflavones shifts

In the chemical shift range for alkenes and aromatic and heteroaromatic compounds enol ether fragments (furan, pyrone, isoflavone, 195-200 Hz) ... 

The NMR spectra of the product do not show these features. The highest C shift value is Sc = 160.9 and indicates a conjugated carboxy-C atom instead of the keto carbonyl function of an isoflavone (5c =175). On the other hand, a deshielded CH fragment at 5c/<5 = 138.7/7.i52 appears in the C NMR spectrum, which belongs to a CC double bond polarised by a -A/effect. The two together point to a coumarin 4 with the substitution pattern defined by the reagents. 

The possible pathways for the transformations 323 -> 324 and 323 - 325 are outlined in Scheme 84. The first step that is common to these reactions involves the electrophilic attack of the I(III) species on the enol form of 323 at the face of the molecule anti to the C(2)-aryl ring to provide intermediate 328. Routes (a) and (a ) involving a 1,2-aryl shift lead to isoflavones 324. Route (b), involving Sn2 attack of X /XH at the C(3)-position of intermediate 328, leads to 325 via 329. The nucleophilicity of X XH plays a deciding role in affecting the course of the reaction. 

However, studies in hypercholesterolemic subjects, using soy protein depleted of isoflavones have shown that soy protein independently of isoflavones can favorably affect LDL size, LDL particle distribution was shifted to a less atherogenic pattern,and can decrease triglyceride concentrations, triglyceride fatty acid fractional synthesis rate, and cholesterol... 

The chemical shift of the single proton of the heterocyclic ring of flavones (22) and isoflavones (64) provides a means of distinguishing the two systems. The H-3 flavone proton (8 6.0-6.5) appears upheld of the isoflavone proton H-2 (6 7.7-8.0) which is deshielded by the heteroatom and in DMSO is shifted further downfield (8 8.S-8.7) (67JHC61). 

In the spectra of isoflavones (64) and flavanones (25), in which rings A and B are not conjugated, band I frequently appears only as a shoulder on band II. Not surprisingly, introduction of oxygen substituents in ring B has little effect on the spectra, whereas substitution in ring A shifts band II to the red. 

Table 5.38 b. Structures and 13C Chemical Shifts (<5C in ppm) of Selected Chalcones, Flavones, Flavonols, Isoflavones, Dihydro-flavones, Dihydroflavonols and Flavons (Aglycones). Spectra were Recorded in DMSO-d6, Except those of Flavone (CDC13) and 2 -Hydroxy-, and 2,2 -Dihydroxychalcone (D20/DMS0-d6 (2 7)) [989, 990]. 

Flavanones - Isoflavones. Although Koser s reagent (1) is known to effect a-tosyloxylation of ketones,1 the reaction with flavanones (2) results in an oxidative 1,2-aryl shift to provide isoflavones (3) in 74-80% yield.2 This conversion has been effected previously with thallium salts. 

In boiling acetonitrile an aryl shift also took place, the only products being isoflavones. 

Isoflavones.- It is often difficult to distinguish between substitution at 5- and 7-positions of benzopyrans. A study of eight isoflavones has shown that 5- and 7-methoxy group n.m.r. signals are shifted by trifluoroacetic acid.11 1 The change in chemical shift induced by benzene on aromatic methoxy groups continues to be used in structure determination.1[Pg.401]

Isoflavones, 3-Bromoflavanones (1) undergo a 2,3-aryl shift when treated with silver hexafluoroantimonate in methylene chloride to form isoflavones (2). ... 

The 5-OH signal of isoflavones appears between 812.5 and 13.5 in acetone-ds (285, 417). The changes in the chemical shift of the 5-OH signal upon hydroxylation at C-2 of isoflavones as well as the effect of prenylation at C-6 or C-8 were reported briefly by us 347), and in detail later by Tahara et al. 417). Hydroxylation at C-2 of a flavone or flavonol causes a downfield shift of the 5-OH signal (Tables 6 and 8) however, the 5-OH signal of 2 -hydroxyisoflavones appears farther upfield than that of 2 -unsubstituted isoflavones or 2 -0-alkyl(alkenyl)-isoflavones (0.16-0.56 ppm. Table 7). 

The utility of these substituent parameters was shown in the structure determination of the minor isoflavones, kanzonols K (183) and L (184), isolated from Glycyrrhiza uralensis (Section 3.1.2). The H NMR and UV spectra (absence of an aluminum-induced shift) of kanzonol K (183) showed that the structure of the compound was 183 or 317 (Fig. 26). Calculated values using the substituent parameters of Table 7 for the 5-OH signal of 183 and 317 are 8 12.68 and 13.14, respectively, as shown in Fig. 26. The chemical shift of the 5-OH of kanzonol K (8... 

Fukai, T, J, Nishizawa, and T. Nomura Phenolic Constituents of Glycyrrhiza Species. 14. Variations in the Chemical Shift of the 5-Hydroxyl Proton of Isoflavones Two Isoflavones from Licorice. Phytochem., 36, 225 (1994). 

Tahara, S.-, J.L. Ingham, F. Hanawa, and J. Mizutani H NMR Chemical Shift Value of the Isoflavone 5-Hydroxyl Proton as a Convenient Indicator of 6-Substitution or 2 -Hydroxylation. Phytochem., 30, 1683 (1991). 

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