Phytochemical Investigations of a Native North American Species, "Acer saccharinum" and an Endemic Saudi Arabian Species, "Euphorbia saudiarabica"
The objectives of this work are the isolation, purification, structure elucidation, and biological evaluation of isolated bioactive secondary metabolites, primarily tannins and diterpenoid compounds, of two known plant species: silver maple (Acer saccharinum) and Euphorbia saudiarabica , respectively. ^ Based on the ethnopharmacological literature, Acer saccharinum is a traditional medicinal plant that has been used by the people of North America. According to previous phytopharmacological studies by our group, over 70 phytochemicals, primarily tannins, and flavonoids have been discovered from three different maple species, including sugar (A. saccharum), red ( A. rubrum), and sycamore (A. pseudoplatanus) maples. Remarkably, the red maple species yielded very interesting bioactive tannins (α-glucosidase inhibitors) named glucitol-core containing gallotannins (GCGs). Therefore, to gain a better understanding of the phytochemical composition of other maple species, such as silver maple, the fresh leaves of silver maple were collected and extracted. After that, the crude extracts of different polarities were prepared and submitted to a preliminary screening using RP-HPLC, TLC, and Folin-Ciocalteau methods for quantifying the polyphenol contents. Then, the isolation procedure was carried out by multiple steps, including OCC, TLC, and RP-HPLC for the higher polyphenolic content extraction (ethyl Acetate extraction). Through HPLC-DAD analyses using previously isolated standards, nine compounds, including six GCGs, were identified as ginnalins A-C ( 1-3), maplexins B, D, and F (4-6), methyl syringate ( 7), methyl gallate (8), and 3-methoxy-4-hydroxyphenol-1-β-D-(6-galloyl)-glucopyranoside (9). Additionally, pubineroid A (10), a sesquiterpenoid, was isolated and identified (by NMR). ^ On the other hand, Euphorbia genus is one of the six largest genera of flowering plants which are known to produce several bioactive secondary metabolites, primarily diterpenes, such as jatrophane and lathyrane. Euphorbia saudiarabica, which is endemic to Saudia Arabia that it is well characterized by the production of a milky irritant latex, is one of the plant species in the region that has not been thoroughly studied. To enrich the knowledge of the constituents of E. saudiarabica, a comprehensive phytochemical investigation was made, leading to the reported of five new lathyrane-type diterpenoids named saudiarabicain A-E. Then these compounds were evaluated for their cytotoxic activity. All of them were evaluated against three tumor cell lines, including Murine B16F10 melanoma cells, Human HaCat Keratinocytes, and Human SH-SY5Y Neuroblastoma cells. In B16F10 melanoma cells, only compounds B, C, and D induced significant toxicity, with the compound B having the greatest range of toxicity from 100 µM (49.63% decrease) to 20 µM (14.69% decrease). In human keratinocytes (HaCat), each compound caused a decrease in cell viability above 40 µM. At a concentration of 30 µM, compounds C and D caused reductions in cell viability by approximately 12.42% and 17.92 %, respectively. Compound C was able to decrease viability by as much as 93.63% at 50 µM. Lastly, in SH-SY5Y cells, all these compounds (A-E) induced a cytotoxic effect at concentrations of 50µM and above. ^ Finally, for the first time, a quantitative analysis of the flavonoids that are present in the methanol extract of aerial parts of E. saudiarabica using LC-ESI-TOF-MS/MS analytical method has been conducted. As a result, 36 flavonoids were identified, 7 flavonoids based on the galangin aglycon, 9 flavonoids based on the apigenin aglycon, and 20 flavonoids originated from luteolin. ^ In conclusion, the work of this dissertation was provided insights about the phenolic contents, primarily tannins, of silver maple (Acer saccharinum ) and were compared to other common maple species, mainly the sugar (A. saccharum), red (A.rubrum), and sycamore (A. pseudoplatanus) maples which were previously investigated by our group. On the other hand, based on the diterpenoids composition, the endemic Euphorbia saudiarabica species from Saudi Arabia yielded five new lathyrane-type of diterpenoids. All of them were evaluated for their cytotoxicity and showed moderate effects. Lastly, a rapid and reliable method employing LC-ESI-TOF-MS/MS was developed for the identification of flavonoids in the aerial parts of E. saudiarabica.^
Abdullatif Bin Muhsinah,
"Phytochemical Investigations of a Native North American Species, "Acer saccharinum" and an Endemic Saudi Arabian Species, "Euphorbia saudiarabica""
Dissertations and Master's Theses (Campus Access).