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Abstract
Cycas is the only currently known genus of the family Cycadaceae,
order Cycadales. Chemical investigation of the constituents of Cycas
revoluta Thunb. and C. circinalis L. leaflets afforded two new
dihydrobiflavone glycosides; I-(2,3)-dihydro-I-7-O-β-Dglucopyranosylamentoflavone
(6) I-(2,3)-dihydro-I-7, II-7-di-O-β-Dglucopyranosylamentoflavone
(7) from C. revoluta and one new
biflavonoid, (2S,2˝S)-2,3,2˝,3˝-tetrahydro-4′,4‴-di-Omethylamentoflavone
(tetrahydroisoginkgetin, 10) from C. circinalis in
addition to thirty compounds, twenty-one of which are isolated for the
first time from the two species. The isolated compounds include fourteen
biflavonoids, three lignans, four flavan-3-ols, six flavonoid glycosides,
two nor-isoprenoids, and one flavanone. This is the first report of NMR
and CD data of 2,3-dihydro-4′-O-methyl- and 2,3,2˝,3˝-tetrahydro-4′-Omethyl-
amentoflavone (4) and (9). The CD spectrum of compound 7
showed a stable atropisomer which is seen for the first time in
amentoflavone class. The effect of O-methylation on the chemical shifts
of the neighboring carbons in the 13C NMR spectra of the dihydro- and
tetrahydro-amentoflavone skeletons is discussed. The structure
elucidation of these compounds was established via HR-ESIMS, CD, 1D
and 2D NMR techniques. Analytical RP-HPLC study of different plant
organs concerning their content of six biflavonoids was done. Results
x
showed the presence of similar biflavonoid picture in the leaflets and the
rachis. The seeds showed the presence of hinokiflavone and its
dihydroderivative which is different from reported data. The isolated
compounds were screened for the cytotoxicity, antimicrobial, and
antiprotozoal activities. The new compound tetrahydroisoginkgetin (10)
showed cytotoxicity to the breast ductal carcinoma with IC50 =12 μg/mL.
Hinokiflavone (15) showed cytotoxicity to the melanoma with IC50 =13.4
μg/mL. Isoginkgetin (14) and dihydrobilobetin (4) showed cytoxicity to
more than one cell lines. Dihydroamentoflavone (3), tetrahydrobilobetin
(9) and the new compound tetrahydroisoginkgetin (10) displayed
moderate antibacterial activity against Staph. aureus (IC50 values of 8.2,
9.6, and 3.8 μM, respectively) and methicillin-resistant Staph. aureus
(MRSA) (IC50 values of 11.5, 12.5, and 5.9 μM, respectively). Vitexin
rhamnoside (21) showed antileishmanial activity of IC50 and IC90 of 13.4
and 34.6 μM compared to pentamidine (2.9, 14.7 μM) and amphoericine
B (0.1, 0.35 μM).
Keywords: Cycadales, Cycadaceae, Cycas revoluta, Cycas circinalis
glycoside, biflavonoid, atropisomer, antimicrobial, cytotoxicity
,antileishmanial.