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991.
Three new A,C-diamide bridged p-tert-butylcalix[6]arenes were synthesized from p-tert-butylcalix[6]arenes by bridging ClCH2CONH(CH2)nNHCOCH2Cl(n=3,4,6) in acetonitrile using K2CO3 as a base in 17%-25% yields.It was found that the bridged calix[6]arenes with shorter bridges (n=2,3,4 in N′,N′-bischloroacetodiamines) adopt cone conformation, but the last one (n=6) adopts alternate conformation, i.e., accompanying the lengthening of bridge, the conformation of A,C-bridged calix[6]arenes changes from cone to alternate. 相似文献
992.
Munakata R Katakai H Ueki T Kurosaka J Takao K Tadano K 《Journal of the American Chemical Society》2003,125(48):14722-14723
The first total synthesis of (+)-macquarimicin A (1), a novel inhibitor of neutral sphingomyelinase (N-SMase) with antiinflammatory activity, has been accomplished. The present work determined the absolute configuration of (+)-1 and revised the C(2)-C(3) geometry to be Z. The synthesis features a transannular Diels-Alder reaction, which constructed the tetracyclic framework stereoselectively, and a convergent and efficient synthetic pathway, which afforded (+)-macquarimicin A (1) in 27 steps (longest linear sequence) with 9.9% overall yield. 相似文献
993.
The fused heterocycle 4-(phenylsulfonyl)-4H-furo[3,4-b]indole, which is an indole-2,3-quinodimethane synthetic analogue, is prepared in five steps from indole in 46% yield. A similar sequence is used to synthesize C-3 derivatives (3-methyl, 3-phenyl, and 3-heptyl). Thus, indole-3-carbaldehyde (1) is protected as the N-phenylsulfonyl derivative 2 and converted to the ethylene acetal 6. Lithiation at C-2 followed by treatment with an aldehyde affords the expected hydroxy acetals 7 and 8. Exposure to acid effects cyclization to the furoindoles 5 and 9. Furthermore, C-1 lithiation of furo[3,4-b]indole 9c followed by treatment with methyl iodide affords disubstituted furo[3,4-b]indole 10. 相似文献
994.
催化裂化干气与苯烷基化催化蒸馏制乙苯反应网络热力学研究 总被引:2,自引:0,他引:2
高温气相反应条件下的催化裂化干气制乙苯过程中,容易生成甲苯和二甲苯等副产物;在该过程中采用催化蒸馏技术,使苯与乙烯在低温条件下进行反应,可大幅度降低产品中二甲苯的含量.通过对催化裂化干气与苯烷基化催化精馏过程中的各反应步骤进行分析与热力学计算,结合反应的实际产物组成,提出了苯与乙烯烷基化的反应网络,探讨了苯与乙烯烷基化反应过程中甲苯和二甲苯的形成机理及影响因素.结果表明,增大苯/乙烯比对提高乙烯平衡转化率及乙苯收率有利;在较低温度下进行烷基化反应,可大大减缓C-C键裂解速度,抑制甲苯和二甲苯生成,提高乙苯产品质量. 相似文献
995.
Nabeshima T Saiki T Iwabuchi J Akine S 《Journal of the American Chemical Society》2005,127(15):5507-5511
Synthesis and binding behavior of a novel multi-responsive host 1, in which two esters, two polyether moieties, two urea sites, and two bipyridine units as ion binding sites are arranged on the calix[4]arene skeleton, is reported. 1 recognizes Na(+) and Ag(+) simultaneously and quantitatively and captures an anionic guest. The ability of 1 to recognize anions, including CF(3)SO(3)(-) and BF(4)(-), remarkably increases in a stepwise manner using Na(+) and Ag(+) as effectors. The enhancement of the K(a) eventually reaches factors of 1500 and 2000 for NO(3)(-) and CF(3)SO(3)(-), respectively, in the presence of both Na(+) and Ag(+), compared to the free 1. The regulation of binding of multiple ligands may be applicable to multistep cascade systems for the amplification of molecular events, and further studies in this field could provide insight applicable to more advanced molecular devices. 相似文献
996.
Jin‐Jun Wang Kimiaki Imafuku Yong Key Shim Gui‐Ji Jiang 《Journal of heterocyclic chemistry》2005,42(5):835-840
Methyl E/Z‐pyropheophorbide‐a 131‐ketoximes 2a,b and their O‐acetyl derivatives 3a,b were oxidized with osmium(VIII) oxide to give aldehydes 4a,b and 5a,b , respectively. The Wittig reactions of the aldehyde chlorines 4a,b and 5a,b with benzyltriphenylphosphonium chloride were performed to form the corresponding methyl (31E/Z,131E/Z)‐32‐phenylpyropheophorbide‐a 131‐ketoximes 6aa‐bb and their O‐acetyl derivatives 7aa‐bb ; hydrolysis of these ketoximes 6aa,ba and 6ab,bb in formic acid produced methyl (E/Z)‐32‐phenylpyropheophorbide‐a's 8a,b . 相似文献
997.
Venkateshrao S Yin J Jarzecki AA Schultz PG Spiro TG 《Journal of the American Chemical Society》2004,126(50):16361-16367
Resonance Raman (RR) spectra are reported for mesoporphyrin IX bound to the Fab fragment of the ferrochelatase antibody 7G12. Binding induces activation of a Raman band at 680 cm(-1), which is assigned to an out-of-plane porphyrin vibration, gamma15. This is exactly the predicted effect of distorting mesoporphyrin to the geometry of N-methylmesoporphyrin IX, the 7G12 hapten, based on DFT/CIS modeling of the RR spectrum. The modeling also shows that the pyrrole ring that is tilted out of the porphyrin plane bears a nitrogen lone pair, which is therefore available for coordination by an incoming metal ion. The 680 cm(-1) band intensity is approximately 3 times higher for the affinity-matured antibody than for the germline precursor antibody, while intermediate values are found for variants in which germline residues are mutated to mature residues or vice versa. Thus, RR spectroscopy reveals an evolution from weak substrate distortion in the germline antibody to strong substrate distortion in the affinity-matured antibody, and supports the view that catalysis involves a substrate strain mechanism. 相似文献
998.
Two new C18-norditerpenoid alkaloids from Aconitum delavayi 总被引:2,自引:0,他引:2
Shan Hao Jiang Hai Qing Wang Yi Ming Li Shuang Jun Lin Jun Jie Tan Da Yuan Zhu 《中国化学快报》2007,18(4):409-411
Further phytochemical investigation of the unique C18-norditerpenoid alkaloids from the roots of Aconitum delavayi Franch ledto the isolation of two new norditerpenoid alkaloids,delavaconitine F 1 and delavaconitine G 2.Their structures were determinedfrom spectroscopic evidence. 相似文献
999.
1000.