Ginkgetin or Isoginkgetin: The Dimethylamentoflavone of Dioon edule Lindl. Leaves

Aims: Phytochemical study of the biflavonoid content of Dioon edule Lindl. leaves in addition to quantification of the phenolic content and evaluation of their antioxidant potential.

Methodology: Chromatographic isolation of the total alcohol extract of the leaves followed by the spectroscopic identification of the isolated compounds was performed adopting 1D, 2D NMR techniques. The total phenolic content (TPC) was determined using the Folin-Ciocalteu method and the total flavonoids content (TFC) was measured by complexation with aluminum chloride and the antioxidant activity was evaluated with DPPH (2.2-diphenyl-1-picrylhydrazyl) assay.

Results: Phytochemical investigation of Dioon edule Lindl. leaves afforded the isolation of 7,4′,7″,4″′-tetramethylamentoflavone (1), 4′,4″′-dimethylamentoflavone (isoginkgetin) (2) biolbetin (3) and amentoflavone (4) in addition to β-sitosterol (5). A more accurate assignment of 13C-NMR data of the methylated amentoflavone derivatives is performed using 2D NMR (HMQC and HMBC). Compounds 2 and 5 are reported for the first time in Dioon edule Lindl. leaves. Previous report on D. edule Lindl. leaves afforded the isolation of ginkgetin (6) as a dimethylamentoflavone but our investigation proved that it is isoginkgetin. The TPC was 0.27±0.01 gallic acid equivalents in mg/g plant material. The TFC was 1.8473±0.077 rutin equivalents in mg/g plant material. The plant exhibited a good antioxidant property as DPPH scavenging activity was 3.29±0.251 mg ascorbic acid equivalent antioxidant capacity in 1 g plant material.

Conclusion: The phytochemical study of D. edule Lindl. leaves afforded isoginkgetin instead of the previously reported ginkgetin. The use of NMR provides the most powerful tool for a more accurate assignment of biflavonoids.