Synthesis And Biological Study Of Chrysogeside B And Its Variants

Cerebrosides as a kind of glycosphingolopids,are abound in the plasma membrane.A large number of cerebrosides were successively found from all kinds of organisms since it was firstly found in the 1940's,and exhibited a wide variety of potential biological pharmaceutical activity.In recent years,some novel structure of cerebrosides were isolated from marine organisms with various biological activity,such as antifungal,antitumor,antivirus,immunomodulatory properties,etc.Because of its unique activities and special structures,natural cerebrosides and their derivatives bacome a hot spot in the total synthesis of natural products and biomedical research.Cerebrosides are difficult to be separated and purified from organisms,which limit the deep study of itselves.There were a large number of literature to report cerebrosides' synthesis,but most of them only was focused on the simple ceramides.There was few report of synthesis of the ceramides containing complex fragments,such as a-hydroxy-?,?-unsaturated carboxylic acid,sphingosines with methyl side chain and multiple unsaturated bonds.In 2011,Peng Xiaoping group reported the Chrysogeside B,which not only had excellent antibacterial activity and cytotoxicity,but also was the first discovery of C19 unsaturated carboxylic acid.This paper designed to synthetize Chrysogeside B and its derivatives,which focused on the impact of free hydroxyl and glycosidic bond for their biological activity.In particular,we uesd chiral induction to design and synthetize the a-hydroxy-?,?-unsaturated carboxylic acid.With the retrosynthesis of Chrysogeside B,we designed to prepare three structural fragments,such as sphingosine,a-hydroxy-p,y-unsaturated carboxylic acid,glycosyl ligant,then coupled three fragments one-by-one.The detailed synthetic pathway was as follows,dihydrogen furan as starting material,after reacted with halogenated alkane coupling reagent and opening-ring of methylmagnesium bromide to get(E)-alcohol.Then(E)-alcohol was halogenated,coupled and desilicated to get terminal alkyne.Further terminal alkyne was added with chiral Garner aldehyde to build the basic skeleton of sphingosine,after Red-Al reduction,protection,deprotection to get sphingosine intermediate.Then sphingosine intermediate was condensated with R-configuration of a-hydroxy-P,y-unsaturated carboxylic acid to get ceramide.After forming the ?-glycosidic bond,sodium methoxide was used in the deprotection,resulting in the target product Chrysogeside B.On the basis of successful synthesis of Chrysogeside B,we also synthesized its analogues.Then KB tests were carried out to test the antibacterial activity of Chrysogesides B and its analogues against Enterobacter aerogenes,Escherichia coli,Xanthomonas oryzae pv.oryzae(Ishiyama),FusaHum graminearum Sehw.,Colletotrchum musae,Citrus Penicillium italicum,and the cytotoxicity of Hala cells by MTT method.The assays results showed that the change of ?-glycosidic bond in Chrysogeside B to the a-glycosidic bond was conducive to improve its antibacterial activity;the existence of free hydroxyl groups was also important on the antibacterial activity.Some assays results also showed removing the sugar ligand could improve its antibacterial activity.Furthermore,considering that(S)-glyceraldehyde acetonide which was similar to Garner aldehyde,should have chiral induction character,we designed and developed a new strategy to synthesize a-hydroxy-?,?-unsaturated carboxylic acid.In this strategy,(S)-glyceraldehyde acetonide(91%ee)which was synthesized from Vitamin C,was employed as chiral induction source,ClTi(Oi-Pr)3 and n-BuLi were used as the coordination agent and bound acid agent,and(R)-alcohol was obtained with high diastereoselectivity in 80%-83%yield.In order to obtain the product with excellent optical purity,(R)-alcohol was esterified with 3,5-dinitrobenzoic chloride,recrystallized with hexane/ethyl acetate(14/1,v/v),and hydrolyzed by anhydrous potassium carbonate,to get the(R)-alcohol with the dr value of 99:1.After reduction of Red-Al,hydroxyl group protection with benzoyl chloride,deprotection with amberlyst 15 and two steps of oxidations,six a-hydroxy-?,?-unsaturated carboxylic acids were successfully obtained with the ee value of 99%and the total yield of 58%.