Synthesis Of (+)-Flubalasubramide Derivatives And Studies On Their Anti-neuroinflammatory Effects

(+)-Flubalasubramide（3c）is a lead compound obtained from the modification of natural product（+）-balasubramide prezent in the Clausena indica.The pharmacological test in the early stage of the research group showed that（+）-3c has a good anti-neuroinflammatory effect.The Mechanism of（+）-3c is to inhibit neuroinflammatory effects by regulating the phenotypic polarization of microglia M₂;thus,it has a beneficial effect on improving the symptoms of ischemic stroke disease.Since（+）-3c is too poor in fat solubility,it is not conducive to the blood-brain barrier,in order to improve the lipid-water distribution coefficient lgP of（+）-3c.In this paper,we designed and synthesized the ester and ether derivatives of the 5-hydroxyl group by using the asymmetric synthesis route of（+）-3c in our laboratory.Using 4-trifluoromethyl trans-cinnamaldehyde as a starting material,（+）-3c was synthesized by three-step reaction of asymmetric epoxidation esterification,esteramine exchange,and intramolecular cyclization.By optimizing the reaction time and temperature,the total yield of the three-step reaction was increased by 42%from the original 38%,and the enantioselectivity was increased from 96%to more than98%.Different group of esterification and etherification on the 5 hydroxyl group of eight-membered lactam ring were designed,according to the principle of structural diversification in drug design.Thus,the esterification and etherification substituents group,including asaturated and unsaturated linear hydrocarbon group,branched hydrocarbon group,an aromatic hydrocarbon group,and a heterocyclic ring were choiced.With dicyclohexylcarbodiimide as condensation agent and 4-dimethylaminopyridine as catalyst,esterified derivatives（3c-01-3c-20）were obtained by esterification of 5-hydroxyl with various substituted carboxylic acids or their anhydrides.The yield of the esterified derivative was 72-85%and the enantioselectivity was 96%.With sodium hydroxide as catalyst,etherified derivatives（3c-21-3c-24）were obtained by etherification of 5 hydroxyl groups with halogenated alkane.The yield of the etherified derivative was 62-68%,and the enantioselectivity was 96%.To explore the stereostructure-activity relationship of（+）-3c and the biological activity of the enantiomer（-）-3c.Using 4-trifluoromethyl benzaldehyde as raw material,（±）-3c was synthesized by Darzens condensation,transesterification and intramolecular cyclization in a total yield of 41.5%.（±）-3c was separated by chemical resolution method,thus,we condensed the 5th secondary hydroxyl group of the eight-membered lactam ring with S-（+）-O-acetyl mandelic acid to obtain two diastereomers.We separate the two diastereomers according to the difference in physicochemical properties.Then,by alkaline hydrolysis,optically active（+）-3c and（-）-3c were obtained,respectively.（+）-3c was get with 27%yield and 94.3%enantioselectivity,and（-）-3c was 28.7%yield,and 93.7%enantioselectivity.The splitting method is simple in operation and high in yield,which provides a methodological basis for further research on the tridimensional relationship of the eight-membered lactam compound in Clausena indica.An anti-neuroinflammation study was performed on（+）-3c derivatives with reference to the pharmacologically active type of（+）-balasubramide.The（+）-3c derivative was subjected to an anti-neuroinflammatory test by an ELISA method.The results showed that except the esterification derivatives（3c-01）,the esterification derivatives（3c-02）and the esterification derivatives（3c-03）,the other derivatives could inhibit the release of inflammatory factor TNFalpha in BV-2 microglia induced by lipopolysaccharide.When 5hydroxyl groups were substituted by 4-trifluoromethylbenzoic acid with strong electronegativity,the esterified derivative（3c-17）had better anti-inflammatory effect.These results suggest that etherification or esterification of 5 hydroxyl groups still have anti-inflammatory effects in varying degrees.In the paper,we have synthesized a total of 36 intermediates and target compounds,including 24 target compounds of esters and ethers,and 24 compounds have not been reported.There were 21 compounds with good anti-inflammatory activity.