Synthesis Of 4'-?-glucosyl-khellactone Analogues

Cancer is one of the major diseases that threaten human life and health.The clinical drugs for cancer treatment mainly come from the extraction of natural products and artificial synthesis.Due to the shortage of plant resources,artificial synthesis of natural anti-cancer products is an effective way to solve this problem.4'-?-glucosyl-khellactone was a chiral compound extracted from toxicaria,and it has been found that it has strong cytotoxic activity against tumor cells.However,due to the depletion of plant resources,and the low content in the toxicaria,then chemical synthesis of 4'-?-glucosyl-khellactone is of great significance.In this thesis,two strategies,double-bond epoxidation followed by acid-induced ring-opening and double-bond oxidation catalyzed by potassium osmate,were used to construct the chiral vicinal diol structural units in khellactone.The hydroxyl group(3'S/3'R)of vicinal diol was selectively protected to obtain compound 9a,8b with a free hydroxyl group(4'R/4'S)using as glycosylation receptor.The hydroxyl group(4'R/4'S)of vicinal diol was selectively protected to obtain compound 8c with a free hydroxyl group(3'S/3'R)using as glycosylation receptor.Similarly,glucosylation receptor 9a with 3?S/3?R-hydroxyl blocked by benzyl ether and 4?R/4?S-hydroxyl free was accomplished by double bond epoxidation followed by benzyl alcohol ring-opening promoted by Lewis acid.Finally,use 2,3,4,6-tetra-O-acetyl-?-D-glucopyranosyl trichloroacetimidate with neighboring group participation effect as a glycosylation donor,which was reacted with glycosylation acceptor to give three sets of 4'-?-glucosyl-khellactone analogues 1a(3?S,4?R)and 1a'(3?R,4?S),1b(3?R,4?R)and 1b'(3?S,4?S),1c(3?S,4?S)and 1c'(3?R,4?R)with high regioselectivity and high stereoselectivitySynthesis and structural characterization of 1a(3?S,4?R)and 1a'(3?R,4?S)as diastereomer analogs of 4'-?-glucosyl-khellactone glycosides.7-hydroxycoumarin and 3-chloro-3-methyl-1-butyne are used as raw materials to obtain the seselin 4.Then double bond epoxidation of seselin was using 3-chloroperoxybenzoic acid as oxidant constructed epoxide 5.Then epoxide 5 was opened with two different methods.Method 1: epoxide 5 was ring-opening in acidic conditions to generate the chiral vicinal diol trans-kenolactone 6a.Method 2: In the presence of indium trichloride,the trans-kenolactone of(4?R/4?S)-hydroxy group protected by benzyl ether was generated to use benzyl alcohol as a nucleophile.In the method 1,the(4?R/4?S)-hydroxyl group of trans-kenolactone was selectively protected by tert-butyldimethyl chloride and the(3?S/3?R)-hydroxyl group was protected acetic anhydride to obtain 8a.The tert-butyldimethylsilyl of 8a was removed with hydrochloric acid to obtain trans-khellactone 9a with the(3?S/3?R)-hydroxyl protected by an acetyl.After the(4?R/4?S)-hydroxyl group of trans-kenolactone was selectively protected by benzyl group(method 2)to give 6a',then (3?S/3?R)-hydroxyl group of 6a' was masked by acetic anhydride to give 8a'.Then compound 9a was obtained from 8a' by catalytic hydrogenation.At last,4?-glycosylated diastereomer mixture 1a(3?S,4?R)and 1a'(3?R,4?S)were obtained as the diastereomer mixture by the glycosylation of 9a with donor 2,3,4,6-tetra-O-acetyl-?-D-glucopyranosyl trichloroacetimidate followed by deacetylation via saturated ammonia-Me OH.The structure of analogs 1a(3?S,4?R)and 1a'(3?R,4?S)and intermediate were characterized by 1H NMR,13 C NMR,g COSY,HSQC and single-crystal diffraction.The results showed that the position of glucose in the analogs 1a(3?S,4?R)and 1a'(3?R,4?S)was the same as the position of glucose in 4'-?-glucosyl-khellactone.They were 4'-position ?-glucosylation products.The diastereomer mixture 1a(3?S,4?R)and 1a'(3?R,4?S)were separated by HPLC to obtain the analogs 1a(3?S,4?R)and 1a'(3?R,4?S).Then the retention time of natural product 4'-?-glucosyl-khellactone and their synthetic analogs 1a(3?S,4?R)and 1a'(3'R,4?S)were conducted by HPLC.The results showed that the retention time of the analog 1a(3?S,4?R)and 4'-?-glucosyl-khellactone were consistent,while the retention time of the analog 1a'(3?R,4?S)and the 4'-?-glucosyl-khellactone were inconsistent.The toxic activity of synthesized analogs 1a(3?S,4?R)and 1a'(3'R,4?S)were assayed by the CCK8 method,and the results showed that analogs 1a(3?S,4?R)and 1a'(3?R,4?S)had low toxic activity to cancer cell A549,Hep G2 and MDA-MB-231.Synthesis and structural characterization of diastereomer analogs 1b(3?R,4?R)and 1b'(3?S,4?S),1c(3?S,4?S)and 1c'(3?R,4?R).Cis-khellactone 5' was built by oxidation of the double bond in seselin using potassium osmate as a catalyst.Then the(4?R/4?S)-hydroxyl group of cis-khellactone was selectively blocked with tert-butyldimethylsilyl chloride to obtain compound 6'.After the(4?R/4?S)-hydroxyl group of compound 6' was masked by benzoylation to obtain compound 7'.The silicon protecting group of compound 7' was removed by triethylamine hydrofluoric acid to give 3'-position benzoyl group protected derivative 8b and the 4?-position benzoyl group protected derivative 8c caused by the migration of benzoyl group from 3'-position to 4'-position.Then,acceptor 8b,8c and glycosylation doner 2,3,4,6-tetra-O-acetyl-?-D-glucopyranosyl trichloroacetimidate were coupled to furnish 9b and 9c,followed by deacetylation and debenzoylation via saturated ammonia-Me OH to give 4?-glycosylated diastereomer mixture 1b(3?R,4 'R)and 1b'(3'S,4'S)and 3?-glycosylated diastereomer mixture 1c(3'S,4'S)and 1c'(3'R,4'R).The structure of analogs 1b(3?R,4?R)and 1b'(3?S,4?S),1c(3?S,4?S)and 1c'(3?R,4?R)and intermediate were characterized by 1H NMR,13 C NMR,g COSY,HSQC and single-crystal diffraction.The results showed that the position of glucose in the analogs 1b(3?R,4?R)and 1b'(3?S,4?S)were the same as the position of glucose in 4'-?-glucosyl-khellactone.They were 4'-position ?-glucosylation products.While the position of glucose in the analogs 1c(3?S,4?S)and 1c'(3?R,4?R)were adjacent position,they were 3'-position ?-glucosylation products.The diastereomer mixture 1b(3?R,4?R)and 1b'(3?S,4?S)were separated by HPLC to obtain the analogs 1b(3?R,4?R)and 1b'(3?S,4?S).Then the retention time of natural product 4'-?-glucosyl-khellactone and their synthetic analogs 1b(3?R,4?R)and 1b'(3?S,4?S)were conducted by HPLC.The results showed that the retention time of the analogs 1b(3?R,4?R)and 1b'(3?S,4?S)and 4'-?-glucosyl-khellactone were inconsistent.In a word,the synthesis methods of diastereomeric analogs still provide a reference value for the chemical synthesis of 4'-?-glucosyl-khellactone.