Design,Synthesis And Cerebrocardiac Vascular Pharmacological Activity Studies Of The Novel Ligustrazine Derivatives

Cerebrocardiac Vascular Disease(CVD) is the common disease that seriously threatens peoples' health and more than half of the death are caused by CVD. World Health Organization (WHO) claims CVD is 'The Top Enemy threatening the World Health'. Therefore, the research and development of cerebrocardiac vascular drugs are the one of important strategies for the medical therapy in the world.Ligustrazine(Lig; tetramethylpyrazine, TMP) is one major efficient component from Chinese traditional medicine herb Ckuanxiong(Ligusticum wallichii Franchat), which is currently widely used in China as a new kind of calcium channel antagonists for the treatment of coronary atherosclerotic cardiovascular disease and ischemic cerebrocardiac vascular disease. Ligustrazine has been reported to inhibit the platelet aggregation, to cause negative chronotropic and inotropic responses on isolated atria, to inhibit vasoconstriction in isolated vascular strips, and to act as a vasodilator, a free radical scavenger, anti-thrombosis and anti-hypertention agent.However, pharmacokinetics studies found that Ligustrazine presented low bioavailability and to be metabolized fast in vivo with short half-life of T_1/2=2.89h, so accumulated toxicity often appeared in the patients for keeping an effective plasma concentration by the frequent administration. Therefore, it is necessary todevelop new generation of the cerebrocardiac vascular drugs from molecular modification of Ligustrazine.Structure-activity relationship studies indicated that pyrazine ring in the molecule of Ligustrazine might largely be the determinant of its pharmacodynamics, while the substituted groups might primarily govern its pharmacokinetics and toxicity. According to hypridization principle and bioisosteric replacement principle in medicinal chemistry, some drug-like groups and pharmacophores can be introduced to the methyl position of Ligustrazine, for acquiring the pharmacologically additive or synergetic effects to improve pharmacokinetic properties.Calcium channel antagonists, such as Cinnarizine and Flunarizine are very important cerebrocardiac vascular drugs currently used in the clinic. A piperazine moiety as a linker is the common characters existed in their molecular structures, which is considered as the functional group for keeping the drugs' potential. Based on the structures of the calcium antagonists above, Ligustrazine can be modified by combination with a piperazine and some pharmacophores or drug-like groups, such as Ligustrazyl, diphenylmethyl, cinnamyl, cinnamoyl and furoyl to form the novel Ligustrazine derivatives. 67 compounds were synthesized, and 39 of them are Ligustrazine acylpiperazine derivatives (A), 25 are Ligustrazine alkylpiperazine derivatives (B), 3 are Ligustrazine amine derivatives (C).In the synthesis, the Ligustrazine derivatives were prepared starting from Ligustrazine. The intermediate 2-hydroxymethyl-3,5,6-trimethylpyrazine (1) was prepared according to our previous work, but with some modification in the recrystallization, in which the crude compound of 2-hydroxymethyl-3,5,6-trimethyl pyrazine was recrystallized from n-hexane to obtain the pure material. The important intermediate 2-chloromethyl-3,5,6-trimethylpyrazine hydrochloride (2) was prepared by the chlorination of 2-hydroxymethyl-3,5,6-trimethylpyrazine with SOC12 in anhydrous CH2CI2, which was then reacted by alkylation, acylation and amination to give the corresponding Ligustrazine derivatives respectively. All the newly synthesized compounds have not been reported in literature, and theirchemical structures were confirmed by IR, *H NMR and ESI-MS.Endothelial cells play a critical physiological role in maintaining normal vessel and organ function. Oxidative stress is a cardiovascular risk factor and contributes significantly to endothelial injury. Therefore, the protection of endothelial cells against damage caused by oxidative stress is a very important therapeutic strategy.Ligustrazine acylpiperazine derivatives A1-A38 have been tested for 1. Stimulating the proliferation of normal vascular endothelial cells. 2. Protecting against hyperoxic acute injury. 3. Antiplatelet aggregation. Ligustrazine is used as the control drug. The viability of normal and injured endothelial cells is assessed by methyl thiazolyl tetrazolium (MTT) assay. The preliminary biological results obtained from our experiments have demonstrated that compounds Al presents an excellent proliferation rate(97.13%) of normal cells at the concentration of 0.2 mmol.L"1, and is more potent than Ligustrazine; the proliferation rate of the injured cells(91. 16%) is much higher than that of Ligustrazine at the concentration of 0.2mmol.L"'; platelet aggregation rate of Al is 3. 02%, which is more potent than Ligustrazine. Cerebrocardiac vascular activities screening tests of Ligustrazine alkylpiperazine derivatives(B) and Ligustrazine amine derivatives(C) are under way.In conclusion, a series of novel Ligustrazine derivatives have been designed and synthesized. Some compounds are found to have better cerebrocardiac vascular activities than Ligustrazine. The preliminary biological results have demonstrated that compound Al is a promising leading compound for developing new generation of the cerebrocardiac vascular drugs.