Studies On Synthesis,anticancer And Antibacterial Activities Of Flavonoids Mannich Base And Carboxylic Acid Derivatives

Flavonoids exhibit a variety of biological activities and pharmacological effects,such as anticancer,antioxidant,anti-inflammatory,antibacterial and cardiocerebrovascular protection.They have attracted extensive attention in the fields of chemistry,pharmacology and medicine.There are great differences in the structure and content of flavonoids from different sources in nature,so it is difficult to extract and purify them.On the other hand,it is also necessary to design and develop new drugs for the treatment of various diseases.Therefore,the synthesis and biological activity screening for various new flavonoid derivatives are of great significance and potential economic value for the further research and development of high-efficiency and low-toxicity drug lead compounds.In view of the fact that Mannich bases and carboxylic groups are important active units of many natural products and medicinal plants,and that they directly affect the solubility,absorption sites and bioavailability of drugs.In this paper,the synthesis and biological activity of a series of flavonoids Mannich base and flavonoid carboxylic acid?ester?derivatives have been studied.Many of the compounds have good anticancer and antibacterial effects.The main research contents are summarized as follows:1.Naringenin was obtained at first by acid hydrolysis of naringin and then reduced to apigenin by dehydrogenation using I₂/pyridine.After protecting the hydroxyl groups on flavonoids with benzyl group,DMDO was employed to oxidize the products to 5,7,4'-tribenzyl flavonol compounds.Finally,under the catalysis of Pd/C/H₂,the benzyl flavonoids were converted to kaempferol through debenzylation process.2.Eighteen secondary amine Mannich base derivatives of flavonoids were obtained by the acid-catalyzed Mannich reaction of flavonoid substrates,such as apigenin,kaempferol,quercetin,myricetin,luteolin and dihydromyricetin,with formaldehyde and some secondary amines?dimethylamine,diethylamine,dipropylamine,pyrrolidine,morpholine,N-methylpiperazine,hexahydropyridine,etc.?.These Mannich bases were then acidified to form salts,resulting in thirteen flavonoid Mannich bases.After that,twenty-two new Mannich base derivatives of flavonoids based on primary amine were obtained by using Mannich base hydrochloride derivatives 5,18,20,35,47 as substrates to undergo amine exchange reaction with primary amines such as thiosemicarbazone,4-methyl thiosemicarbazone,ethanolamine,isopropanolamine,ethylenediamine,and propylenediamine,etc.3.The optimum conditions were found and established for Mannich reaction and amine exchange reaction.The S_N2 reaction mechanism of amine exchange reaction was well understood in detail based both on the experimental data and on the quantum chemistry theory.The experimental data and phenomena indicate that the amine-exchange reaction is in line with the S_N2 reaction characteristics,and it is found that hydrogen bonding plays a key role in the reaction.In order to investigate the complex effects of hydrogen bonds on the reaction,the density functional theory?DFT?method was used to calculate and simulate a series of amine molecules,Mannich bases and their reaction processes by using the Gaussian09 program.After optimizing the molecular geometry,the frequency,molecular orbital,natural bond orbital and charge distribution,bond energy and bond order are calculated.The structure and reaction path of transition states for some selected representative systems were analyzed by using intrinsic reaction coordinates?IRC?.The hydrogen bond parameters and their variation characteristics in the reaction process were also investigated.Moreover,the activation energies were calculated to evaluate the difficulty and extent of the reaction.The results of these theoretical calculations well explain and support the experimental phenomena,thus revealing the crucial role of hydrogen bonds in the exchange reaction of amino groups and the preference patterns of hydrogen bonds on the amine molecules involved in the exchange.4.The antitumor and antibacterial activities of the synthesized flavonoid Mannich base derivatives and flavonoid substrates were tested by MTT colorimetry and Oxford cup method in vitro.Some patterns and rules of substitution and activity of Mannich base are discussed by means of comparison and analysis.?1?In terms of anti-tumor properties,the type and position of substituents on flavonoid molecules have some effects on their activity intensity.For example,the anti-cancer activity of N-diisopropyl derivatives in Mannich base is stronger than that of N-dimethyl derivatives.?2?The presence of-CH₃ at the end of the substituent is beneficial to the improvement of anticancer activity.?3?But the presence of polar groups such as terminal-NH₂ or-OH is not conducive to the improvement of anticancer activity.?4?In flavonoid substrates,hydroxyl on C3 atom of C ring is helpful for the anti-HeLa activity,the anti-HCC1954 activity and the anti-MCF-7 activity,but not for the anti-SK-OV-3 activity.The double bond between C2 and C3 was also found to be beneficial to the anticancer activity.?5?No positive correlation was found between the number of hydroxyl groups in B ring of flavonoids and their anticancer activity.In general,however,molecules containing 3'-OH and 4'-OH tend to have good anticancer activity.When it comes to antibacterial properties?against Escherichia coli,Pseudomonas aeruginosa,Staphylococcus aureus,and Candida albicans?,?1?Flavonoid Mannich bases with amino residues such as?Methyl-?thiosemicarbazide,dipropyl,pyrrolidine and hydropyridine in molecular structures tend to have good antibacterial activity,while the antibacterial activities of those flavonoid derivatives with dimethyl and morpholine groups are not improved compared with their corresponding flavonoid substrates.?2?In most cases,the increase in the number of phenolic hydroxyl groups is also beneficial to the improvement of antibacterial activity,but the situation of myricetin and quercetin is not exactly consistent with this.5.A series of flavonoid carboxylic acid derivatives and their methyl ester derivatives were prepared by Williamson ether synthesis,and their antitumor and antibacterial activities were tested in vitro?the strains and cancer cell lines selected are the same as those mentioned above?.The results showed that the anticancer activity of flavonoid carboxylic ester derivatives was higher than that of corresponding flavonoid substrates.In terms of antibacterial activity,the carboxyl group can improve the antibacterial activity of the compounds in most cases.