The phase transfer catalysed synthesis of isoflavone-O-glucosides

Acylated Flavone Glucosides: Synthesis, Conformational Investigation, and Complexation Properties

“…Since the tg conformation in glucose units is strongly destabilized by 1,3-syn periplanar repulsions between C(4'')ÀO and C(6'')ÀO bonds, H pro-R ÀC(6'') can be identified as the proton at C(6'') displaying the larger J(5,6) value, an assignment confirmed by selective deuteration experiments [12]. The gt conformation actually places HÀC(5'') and H pro-R ÀC (6) in an antiparallel arrangement, allowing a strong spin-spin coupling, and also orients the acyl moiety toward the flavone nucleus, thus favoring aryl-aryl interactions. The J(5,6 pro-R ) value in (D 6 )DMSO is 7.4 Hz in 2 and 3, whereas it is only 3.7 Hz in 1.…”

“…K 2 CO 3 /CH 2 Cl 2 , tris[2-(2-methoxyethoxy)ethyl]amine, 408) [5]. Similar conditions were also used in the glycosidation of isoflavones [6]. The HOÀC(5) group, which is strongly H-bonded to the C(4)O group (d 12 ± 13 ppm in (D 6 )DMSO), does not react under our conditions.…”

“…Such differences point to a higher fraction of gt conformation in 2 and 3 with respect to the gg conformation. From a modified Karplus equation relating J(5,6 pro-R ) to the fractions of gg and gt conformers [6], and assuming no tg conformer in agreement with a non-measurable coupling constant between HÀC(5'') and H pro-S ÀC(6''), 77% of gg conformer can be estimated for 1, whereas 60% of 2 and 3 would adopt the gt conformation. It is also noteworthy that H pro-S ÀC(6) is strongly deshielded with respect of H pro-R ÀC(6) in the acylated flavones as a consequence of the magnetic anisotropy effect of the CO bond.…”

Synthesis and Biological Study of O-β-D-Glucosides of 7-Hydroxy-3-(disubstituted Imidazol-2-yl)-4H-chromen-4-ones

“…We tried to deacetylate of 4a-i by standard procedure using NaOMe/MeOH; [29] however, we found that the strong basic condition resulted in cleavage of the isoflavone's C-ring, while the anhydrous zinc acetate in absolute methanol system led to significant deglycosylation. Finally, complete deacetylation of 4a-i was achieved by using anhydrous zinc acetate in absolute methanol yielded corresponding o-β-d-glucosides 5a-i in good yields.…”

Microbial Glycosylation of Flavonoids

“…An example of chemical synthesis of flavonoids may be the reaction of isoflavones, such as daidzein, genistein, formononetin or biochanin A with α-tetraacetylbromoglucose in the presence of tetrabutylammonium bromide as a catalyst, leading to O-glucosides of the mentioned aglycones (Lewis et al, 1998) (Fig. 1).…”