Carboxymethyl flavonoids and a chromone with antimicrobial activity from Selaginella moellendorffii Hieron.

Five new carboxymethyl flavonoids named 5-carboxymethyl-3′, 4′, 7-trihydroxyflavone ( 1 ), (2 S )- 5-carboxymethyl-3′, 4′, 7-trihydroxyflavonone ( 2a ), (2 R )-5-carboxymethyl-3′, 4′, 7-trihydroxyflavonone ( 2b ), (2 S )-5-carboxymethyl-4′, 7-dihydroxyflavonone ( 3 ), 5- carbomethoxymethyl-4′, 7-dihydroxyflavone ( 4 ), and a new chromone named 5-carboxymethyl-7-hydroxychromone ( 5 ), together with two known compounds 5-carboxymethyl-4′-hydroxyflavone-7- O - β - d -glucopyranoside ( 6 ), 5-carboxymethyl-4′, 7-dihydroxyflavone ( 7 ) were isolated from Selaginella moellendorffii Hieron. Their structures including absolute configuration were elucidated by extensive spectroscopic methods and experimental electronic circular dichroism (ECD) spectra. What's worth mentioning is that a carboxymethyl substituent appeared at the C-5 position of all isolated compounds, only recently discovered in genus Selaginella . Compounds 2a and 2b were identified as a pair of chiral isomers; compound 5 was discovered as the first chromone comprising a carboxymethyl side chain. Furthermore, all compounds were evaluated for their antibacterial activities against various Gram-positives and Gram-negatives, and compared to the reference drugs amoxicillin and norfloxacin. As a result, compounds 3 and 4 exhibited as potent antimicrobial agents with a broad spectrum, and compound 5 appeared as the most promising one to combat Gram-positives. [ABSTRACT FROM AUTHOR]