关键词： PYRIMIDINES   PYRIMIDINE nucleotides   ORGANIC compounds   GLYCOSYLATION   RING formation (Chemistry)   CHEMISTRY  

摘要： Novel thioiso pyrimidine and purine nucleosides substituted with exocyclic methylene have been synthesized, starting from D-xylose. The glycosyl donor 14 was synthesized from D-xylose, using cyclization of dimesylate 10 with sodium sulfide as a key step. Cyclization proceeded in pure S(N)2 reaction without going through S(N)1 reaction in the presence of an allylic functional group at low reaction temperature (0 degreesC) in polar solvent (DMF), affording compound 12 as a major product. At higher temperatures, S(N)2' product 11 was almost exclusively obtained as a major product. On the other hand, glycosylation of 14 with 6-chloropurine under Mitsunobu conditions afforded the desired SN2 product 26, while palladium-catalyzed glycosylation resulted in the sole formation of S(N)2' product 34.

关键词： Catalysis   Catalysts   glycine derivative   Asymmetric synthesis   acids   Alkylation  

摘要： A recyclable fluorous chiral phase-transfer catalyst was synthesized and successfully applied for the catalytic asymmetric synthesis of both natural and unnatural alpha-amino acids. The reaction involves alkylation of a glycine derivative followed by extractive recovery of the chiral phase-transfer catalyst using fluorous solvent.

关键词： ALCOHOLS (Chemical class)   ORGANIC compounds   METHYLATION   ALKYLATION   ASYMMETRIC synthesis   CHEMISTRY  

摘要： Treatment of the bis(allylsulfoximine)titanium complexes derived from the beta-methyl-substituted acyclic allylic sulfoximines 13a and 13b with aldehydes gave with high selectivities the corresponding sulfoximine-substituted homoallylic alcohols which were isolated as the silyl ethers 15a-h. Methylation of sulfoximines 15a-h afforded the aminosulfoxonium salts 5a-h which upon treatment with LiN(H)tBu gave in high yields the enantio- and diastereomerically pure silyl-substituted 2,3-dihydrofurans 4a-h. Treatment of the titanium complexes derived from the cyclic allylic sulfoximines 17a, 17b, and ent-17c with p-MeOC6H4-CHO delivered with high selectivities the corresponding sulfoximine-substituted cyclic homoallylic alcohols which were isolated as the silyl ethers 18a, 18b, and ent-18c, respectively. Methylation of sulfoximines 18a, 18b, and ent-18c furnished the aminosulfoxonium salts 8a, 8b, and ent-8c, respectively, whose treatment with LiN(H)t-Bu gave the enantio- and diastereomerically pure fused bicyclic 2,3-dihydrofurans 6a, 6b, and ent-6c, respectively, in good yields. It is proposed that the 1-alkenyl aminosulfoxonium salts 5a-h, 8a, 8b, and ent-8c react with the base under a-elimination and formation of the acyclic and cyclic beta-silyloxy alkylidene carbenes 2a-h, 7a, 7b, and ent-7c, respectively, which then undergo a 1,5-O,Si-bond insertion and 1,2-silyl migration. The cyclic aminosulfoxonium salts 8a, 8b, and ent-8c upon treatment with 1,8-diazabicyclo[5.4.0]-7-undecene did not undergo an a-elimination but suffered a novel migratory cyclization with formation of the enantio- and diastereomerically pure bicyclic tetrahydrofurans 9a, 9b, and ent-9c, respectively. It is proposed that the 1-alkenyl sulfoxonium salts 8a, 8b, and ent-8c are isomerized to the allylic aminosulfoxonium salts 10a, 10b, and ent-10c, respectively, which then suffer an intramolecular substitution of the (dimethylamino)sulfoxonium group by the silyloxy group followed by a desilylation.

关键词： ORGANOSULFUR compounds   SULFONES   ASYMMETRIC synthesis   DIASTEREOISOMERS   PALLADIUM   ORGANIC chemistry  

摘要： Described is an asymmetric synthesis of cyclic and acyclic allylic S-aryl and S-alkyl sulfones through a highly selective palladium(0)-catalyzed 1,3-rearrangement of racemic allylic sulfinates. Treatment of racemic cyclic and acyclic allylic S-tolyl- and S-tert-butylsulfinates with Pd-2(dba)(3).CHCl3 as precatalyst and N,N'-(1R,2R)-1,2-cyclohexanediylbis[2-(diphenylphosphino)benzamide] as ligand for the palladium atom afforded the corresponding isomeric allylic S-tolyl and S-tert-butyl sulfones of 93-99% ee in 82-96% yield. The rearrangement of the allylic sulfinates most likely proceeds in an intermolecular fashion via formation of a cationic pi-allylpalladium complex and the sulfinate ion. The racemic allylic sulfinates were obtained from the corresponding racemic alcohols and racemic tolylsulfinyl chloride and racemic tert-butylsulfinyl chloride, respectively, in high yields. Rearrangement of the racemic tert-butylsulfinic acid 2-cyclooct-1-enyl ester with Pd-2(dba)(3).CHCl3 and the bisphosphane was accompanied by a highly selective kinetic resolution of the substrate and gave at 50% conversion the (R)-configured sulfinate as mixture of the S-S and R-S diastereomers of 92% ee and 85% ee and the (S)-configured 3-tert-butylsulfonyl cyclooctene sulfone 15a with 98% ee in almost quantitative yields.

关键词： Redox reactions   Alcohols   Enantioselective synthesis   Catalysts   Metathesis  

摘要： Amino keto-2,7-dienes undergo ring-closing metathesis (RCM) to give 4-aminocyclopentenones, valuable intermediates in the asymmetric construction of carbocyclic nucleosides. The key amino ketodienes were prepared using delta-amino beta-ketophophonates, a new sulfinimine-derived chiral building block, and HWE chemistry.

关键词： Peptides and proteins   Monomers   Enantioselective synthesis   Catalysts   Receptors  

摘要： Utilizing our lateral metalation coupled with Jacobsen's catalytic asymmetric amino nitrile synthesis, we have demonstrated the ability to synthesize isoxazole-containing amino acid glutamate analogues in high yield and high enantiomeric excesses. Chiral centers alpha or beta at the C-5 position do not detract from diastereoselectivity of the Jacobsen-Strecker reaction.

关键词： Alkylation   Allyl Compounds/chemistry   Animals   Cyclization   Models, Molecular   Naphthoquinones/chemical synthesis   Naphthoquinones/chemistry   Palladium/chemistry   Porifera/chemistry   Stereoisomerism  

摘要： Hamigeran B (1), a metabolite isolated from the poecilosclerid spongeHamigera tarangaensis Bergquist and Fromont, exhibits 100% virus inhibition against both herpes andpolio viruses with only slight cytotoxicity throughout the host cells. Its structural motif combinedwith the biological activity stimulates the development of a practical synthesis that canfacilitate exploration of the chemical biology of such structural types represented by these scarcenatural products.

关键词： ESTERS   ORGANIC synthesis (Chemistry)   UNSATURATED compounds   DIASTEREOISOMERS   ADDITION reactions   NITROGEN  

摘要： Chiral nonracemic beta-amino esters were prepared in good yields and enantioselectivities using the diastereoselective conjugate addition of nitrogen nucleophiles to alpha,beta-unsaturated amides derived from (SS)-(+)-pseudoephedrine as the key step. In this way, several Beta-amino amide adducts were prepared using different conjugate acceptors and two different lithium benzylamides as nucleophiles. These adducts were easily converted in only one step, into the final, highly enantioenriched beta-amino esters.

关键词： 手性技术   手性药物   不对称合成   不对称催化   手性化合物  

摘要： 手性(Chirality)[1]是指一个物体不能与其镜中的影像相重合,就如同人的左手与右手,彼此互为实物与镜像的关系而不能重叠.自然界中很多物质都是具有手性的,天然存在的糖都是D型的,氨基酸是L型的,蛋白质和DNA是右旋的.因此,手性是宇宙界的普遍特征,是自然界的本质属性之一.

关键词： L-苯丙氨酸   L-组氨酸   手性环二肽   环(L-苯丙-L-组)   环(D苯丙-D-组)   不对称合成  

摘要： 环二肽是不对称氰醇化反应的重要催化剂。以L 苯丙氨酸、L 组氨酸和D 苯丙氨酸、D 组氨酸为原料,用苄氧羰基保护苯丙氨酸的N端和进一步用硝基苯酚酯活化其C端,再与C端保护的组氨酸甲酯缩合,得直链二肽,再经Pd/C催化氢化脱保护基,闭环,得环(L 苯丙 L 组)二肽和(D 苯丙 D 组)二肽,结构经元素分析、IR、HNMR等证实。