Bioactive Formylated Flavonoids from Eugenia rigida: Isolation, Synthesis, and X-ray Crystallography

Abstract

Two new flavonoids, rac-6-formyl-5,7-dihydroxyflavanone (1) and 2',6'-dihydroxy-4'-methoxy-3'-methylchalcone (2), together with five known derivatives, rac-8-formyl-5,7-dihydroxyflavanone (3), 4',6'-dihydroxy-2'-methoxy-3'-methyldihydrochalcone (4), rac-7-hydroxy-5-methoxy-6-methylflavanone (5), 3'-formyl-2',4',6'-trihydroxy-5'-methyldihydrochalcone (6), and 3'-formyl-2',4',6'-trihydroxydihydrochalcone (7), were isolated from the leaves of Eugenia rigida. The individual (S)- and (R)-enantiomers of 1 and 3, together with the corresponding formylated flavones 8 (6-formyl-5,7-dihydroxyflavone) and 9 (8-formyl-5,7-dihydroxyflavone), as well as 2',4',6'-trihydroxychalcone (10), 3'-formyl-2',4',6'-trihydroxychalcone (11), and the corresponding 3'-formyl-2',4',6'-trihydroxydihydrochalcone (7) and 2',4',6'-trihydroxydihydrochalcone (12), were synthesized. The structures of the isolated and synthetic compounds were established via NMR, HRESIMS, and electronic circular dichroism data. In addition, the structures of 3, 5, and 8 were confirmed by single-crystal X-ray diffraction crystallography. The isolated and synthetic flavonoids were evaluated for their antimicrobial and cytotoxic activities against a panel of microorganisms and solid tumor cell lines.

Synthetic flavonoids with antimicrobial activity: a review

“…The individual synthesis of ( S )‐ and ( R )‐enantiomers of 8 and 9 has been reported (Zaki et al . ) (Fig. ).…”

“…2′,4′,6′‐Trihydroxychalcone, 3′‐formyl‐2′,4′,6′‐trihydroxychalcone and the corresponding 3′‐formyl‐2′,4′,6′‐trihydroxydihydrochalcone and 2′,4′,6′‐trihydroxydihydrochalcone have been synthesized and evaluated for their antimicrobial activity (Zaki et al . ). Antifungal activity was observed for 3′‐formyl‐2′,4′,6′‐trihydroxychalcone ( 11 ) (Fig.…”

Isolation and Structure Identification of Flavonoids

“…As reported in literature [29], the absolute configurations of the enantiomeric flavanone pair (2S)-6-formyl-5,7-dihydroxyflavanone (1a) and (2R)-6-formyl-5,7-dihydroxyflavanone (1b) were assessed via their chiroptical data. The ECD curves of compound (1a) showed sequential positive and negative cotton effects near 310 and 280 nm for the n!π*a n dπ!π* electronic transitions, respectively.…”

Isolation and Structure Characterization of Flavonoids

“…HPLC have been published so far, and some of these compounds, recently reported, are documented in Table 1 as well as their sources, column characteristics and mobile phases used ( Table 1 and Eugenia rigida using CPTLC and prep. HPLC [50]. Flavoalkaloids and flavonol glucosides were reported from Astragalus monspessulanus using the combination of CC, low-pressure liquid chromatography (LPLC) and prep.…”