Design, Synthesis And Neuroprotective Activity Assay Of Carnitine Esters As Prodrug

Partâ… .Research backgroundL-carnitine(L-4-N-trimethylammonium-3-hydroxybutyric acid,LC),a natural amino acid substance and widespread in the tissues of animals,plants and microorganisms,plays vital roles in human nutrition and therapeutics.The primary role of it is to transport long-chain fatty acids across the mitochondrial membrane, where they undergo beta-oxidation to produce energy.It can be also named as novain or VitB_T owing to its vitamin properties.L-carnitine was firstly found from the extract of meat by two Russia scientists, Gulewitch and Krimberg in 1905.However,its mechanisms of action were revealed until 1950s.In the 1970s,with the discovery of the first carnitine-lacking case,its clinical application was eventually recognized.As a result,many derivatives of L-carnitine have been developed,such as L-acetylcarnitine, L-propionylcarnitine,L-citricylcarinitine,etc.In the late 1990s,with the development of cloning techniques,many kinds of transportase of carnitine were found and cloned,leading to a new stage of carnitine associated research fields,e.g.cytoprotection,antioxidation,biological metabolism, etc.Nowadays,many important L-carnitine derivatives have been reported to be applied in such fields as sports nutrition,myocardial Protection,assistant treatment of diabetes dialysis or anti-cancer,anti-senility,endocritic regulation,newborn nutrition,and so forth.In the 21st century,with the discovery and cloning of nearly ten transportases of carnitine,mechanism research of carnitine has reached another new tide.These newly discovered transportases are able to transport L-carnitine and its derivatives to every parts of human body.Moreover,in view of the excellent safety,solubility, and widely biological activities of canitine itself,it might have profound developing value as potential therapeutic drugs as a natural good pharmaceutical carder.Therefore,L-carnitine and its various derivatives may be effective in decreasing toxicity of drugs,improving logP values,penetrating different biological barriers,and increasing the bioavailability.Partâ…¡.Rational Design of Target CompoundsAccording to the recent development of the chemical & biological characteristics,and also the latest progress of clinical application of carnitine and its corresponding derivatives,we noticed an interesting fact that their neuroprotective effects as superior drug delivery system to easily cross the blood-brain barrier has been discovered since 2000.As a consequent focus of attention,these kinds of compounds have recently been used to treat some cerebral diseases such as Alzheimer's disease,Parkinson disease,etc.Based on these undoubting facts and the principle of prodrug,we modify the chemical structure of L-carnitine,which is considered as a useful carder lead compound,to synthesize a series of L-carnitine derivatives,and the modification are as followings:(1) Preparation of prodrug by introducing fatty acid into hydroxyl group of L-carnitine; (2)Preparation of double-prodrugs by re-introducing alcohol and amine side chains into carbonyl group of L-carnitine;(3)Preparation of target compounds by introducing active molecular fragments into carbonyl group of L-carnitine,by the guidance of the principle of combination.Partâ…¢.The Synthesis of Newly Designed Target CompoundsConsidering that L-carnitine is a straight-chain low-molecular containing only four carbon atoms,three active groups,and one chiral center,we discovered a novel reaction mechanism based on these chemical characteristics and consulting of literatures,three series of target compounds were finally accomplished.For the fast series compounds,starting with L-carnitine,the acylcarnitine were obtained through esterification,condensation with different sorts of fatty acids.Based on these compounds,the second and third series were obtained by further condensation reactions.Seven compounds of the fast series and the second,the third series were not reported in the literature.All the compounds have been identified by IR,¹H NMR, and electrospray ionization mass spectrometry(ESI-MS)methods.Partial compounds are further identified by the methods of ¹³H NMR,elemental analysis and X-ray diffraction.Partâ…£.Biological Evaluation of Target CompoundsThe in vitro and in vivo preliminary neuroprotective activity evaluations were performed by using the newly synthesized 40 target compounds.The experimental results displayed that in view of the L-acylcarnitine benzoic ester series compounds,their strong hydroscopicity properties are dramatically improved,under the circumstances of maintaining the efficacy.What's more, among the L-acylcarnitine Ligustrazine ester and N,N-dimethyl ethanolamine ester series compounds,there are approximately 10 compounds have neuroprotective activities.More importantly,these compounds have superior activities than the Ligustrazine,N,N-dimethyl ethanolamine,which are generally acknowledged neuroprotective drugs.Thereby,from our experimental results above,we may safely draw the conclusion that our newly designed and synthesized L-carnitine derivatives have achieved our expectations with potential market applications.Moreover,the additional study on acute toxicity and general pharmacological experiments of L-propionylcarnitine indicated no obvious toxicity and side effect. We therefore can draw a conclusion that it belongs to innoxious substance according to the classified criterion of chemicals. Partâ…¤.Conclusion & ProspectIn conclusion,a beneficial attempt on the prodrug study was conducted through designing,synthesizing three series of L-carnitine derivatives.Our results indicated that the designing route is reasonable and convenient,and meanwhile, owing to the easily available and cheap prices of the raw materials,our research is helpful to develop L-carnitine derivatives to be useful drugs with neuroprotective activities.Further in vivo experiments on the potential compounds are going to be assayed and evaluated in the near future through establishing appropriate animal models.Furthermore,we will deep study their in vivo activities and metabolic process so as to find therapeutic drugs with crucial clinical significance.