Pharmacological Aspects and HPLC Profile of Three Egyptian Seaweeds via Phenolic Compounds; Unraveling Structure-Activity Relationships

This study was designed to give comparative investigations on the total phenols (TPC), tannins (TTC), and flavonoids (TFC) content in <i>Ulva compressa, Pterocladia capillacea,</i> and <i>Colpomenia sinuosa</i> using three different solvents (methanol, ethyl acetate, and hexane). The maximum values of TPC and TFC were found in the ethyl acetate extract of <i>C. sinuosa</i>, with contents of 49.997 mg/g and 38.68 mg/g, respectively. The methanolic extract of all three selected species showed the highest yield of TTC, with a maximum yield of 19.36 mg/g for <i>C. sinuosa</i>. Conversely, the hexane extracts exhibited the lowest phenolic content and bioactivity. Algal extracts were also identified using high-performance liquid chromatography (HPLC), revealing sixteen phenolic acids and flavonoids, including important compounds like gallic acid, cinnamic acid, and catechin in most algal extracts, particularly in methanol and ethyl acetate extracts. The study suggests that ethyl acetate and methanol extracts of <i>C. sinuosa</i> and <i>P. capillacea</i> could serve as valuable sources of natural polyphenols with antioxidant, antidiabetic, anti-arthritic, and anti-inflammatory properties. Strong correlations were observed between flavonoid content and antioxidant and antidiabetic activities. Additionally, flavonoids were supported by structure-activity relationships (SARs) as antioxidants and antidiabetic agents through hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET). The methanol and ethyl acetate extracts from the species studied exhibited an anticoagulant effect, indicating that they could be used as natural anticoagulants. However, further toxicological and clinical research is necessary before considering these algal extracts as nutraceuticals and pharmaceuticals.