A Simple Biomimetic Synthesis of dl-Chamaejasmine, a Unique 3,3‘-Biflavanone

Polyphosphoric acid-promoted one-pot synthesis and neuroprotective effects of flavanones against NMDA-induced injury in PC12 cells

We report herein an efficient polyphosphoric acid (PPA) promoted one-pot protocol for the synthesis of flavanone derivatives from 2-hydroxyacetophenones and benzaldehydes. A variety of flavanones were produced in moderate to excellent yields and evaluated for their neuroprotective effects against N-methyl-d-aspartate (NMDA)-induced excitotoxicity in PC12 cells. Derivatives bearing electron-donating groups exhibited better neuroprotective activity. Compound 3m demonstrated the best protective potency and reversed the intracellular calcium (Ca²⁺) influx caused by NMDA, suggesting that flavanones protected the PC12 cells against NMDA-induced neurotoxicity via inhibition of Ca²⁺ overload.

Selectfluor-Mediated Stereoselective [1 + 1 + 4 + 4] Dimerization of Styrylnaphthols

Stereoselective [1 + 1 + 4 + 4] dimerization of 1-styrylnaphthols has been developed by using Selectfluor as the oxidant for the first time. The reaction was compatible with various functional groups, giving a class of ethanodinaphtho[b,f][1,5]dioxocines with novel 3D skeletons. DFT calculations indicate that this method merges an intriguing stereoselective intermolecular 1 + 1 radical coupling to construct a bridged C-C bond and then an intramolecular [4 + 4] formal cycloaddition of the in situ generated o-quinone methide intermediate.

Liquid Chromatographic Separation of Novel 4-Amino-Flavanes Series Diastereomers on a Polysaccharide-Type Chiral Stationary Phase

Two broad approaches for the syntheses of a series of 4-aminoflavanes are used in this study, and they have been prepared in 30-99% overall yields using the reductive condensation of flavanone with primary amine, as a key step. By this methodology, the formyl derivatives of several secondary amines were obtained in good to excellent yields. The structures of all new products have been confirmed by spectral experiences (IR, ¹H NMR and ¹³C NMR). However, the present non-stereoselective synthesis results in a mixture of 2-7: diastereomers, which differ from the configuration of the flavanone atom asymmetric center. Since each diastereomer may have different biological activity and pharmacokinetic profile, analytical methods have to be developed for their separation. The 4-aminoflavanes diastereomers were separated using polysaccharide chiral stationary phases columns consisting of cellulose (Chiralcel^® OD-H and Chiralcel^®OJ) by high-performance liquid chromatography; the separation was affected by the nature and concentration of the alcohol modifiers in the mobile phase. Separations were carried out under normal phase mode on the Chiralcel^®OJ column. This method can properly separate the two diastereoisomers (Rs > 2) within an analysis time of <50 min.

Synthesis of 3,3′-carbonyl-bis(chromones) and their activity as mammalian alkaline phosphatase inhibitors

Hitherto unknown 3,3′-carbonyl-bis(chromones) 8, dimeric chromones bridged by a carbonyl group, were prepared by reaction of chromone-3-carboxylic acid chloride with 3-(dimethylamino)-1-(2-hydroxyphenyl)-2-propen-1-ones 9.

Synthesis of 3-benzylidene-dihydrofurochromen-2-ones: promising intermediates for biflavonoid synthesis

A route to 3-benzylidene dihydrofurochromen-2-ones from 2H-chromenes is described. Lactonization of 2H-chromenes was achieved using a two-step cyclopropanation-rearrangement sequence. Subsequent conversion of these intermediates to the corresponding α-benzylidene lactones was achieved by lithium enolate Aldol reaction, followed by base-promoted elimination of the aldolate mesylates. The alkene geometry was found to be base-dependent. While KO t Bu favored formation of the E-isomer, DBU showed a slight preference for the Z-isomer. In further studies, these 3-benzylidene dihydrofurochromen-2-ones were converted to polyaromatic structures possessing all the required functionality for biflavonoid synthesis.

Synthesis of biologically relevant biflavanoids--a review

Recent investigations show that naturally occurring biflavanoids possess anti-inflammatory, anticancer, antiviral, antimicrobial, vasorelaxant, and anticlotting activities. These activities have been discovered from the small number of biflavanoid structures that have been investigated, although the natural biflavanoid library is likely to be large. Structurally, biflavanoids are polyphenolic molecules comprised of two identical or non-identical flavanoid units conjoined in a symmetrical or unsymmetrical manner through an alkyl or an alkoxy-based linker of varying length. These possibilities introduce significant structural variation in biflavanoids, which is further amplified by the positions of functional groups--hydroxy, methoxy, keto, or double bond--and stereogenic centers on the flavanoid scaffold. In combination, the class of biflavanoids represents a library of structurally diverse molecules, which remains to be fully exploited. Since the time of their discovery, several chemical approaches utilizing coupling and rearrangement strategies have been developed to synthesize biflavanoids. This review compiles these synthetic approaches into nine different methods including Ullmann coupling of halogenated flavones, biphenyl-based construction of biflavanoids, metal-catalyzed cross-coupling of flavones, Wessely-Moser rearrangements, oxidative coupling of flavones, Ullmann condensation with nucleophiles, nucleophilic substitutions for alkoxy biflavanoids, and dehydrogenation-based or hydrogenation-based synthesis. Newer, more robust synthetic approaches are necessary to realize the full potential of the structurally diverse class of biflavanoids.