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Yoshimitsu H Nishida M Qian ZZ Lei ZH Nohara T 《Chemical & pharmaceutical bulletin》2000,48(6):828-831
Four new triterpene glycosides were isolated from the dried aerial parts of Thalictrum squarrosum (Ranunculaceae). They were designated as squarroside I, being a cycloartane-type glycoside, and squarrosides II, III and IV, being oleanene-type glycosides. Their structures were established by using two dimensional (2D) NMR techniques. 相似文献
4.
Yoshimitsu Itoh 《Tetrahedron》2006,62(30):7199-7203
It has generally been believed that highly basic Li enolates cannot be applied as substrates for radical trifluoromethylation due to defluorination of the α-CF3 product. However, Li enolates can be in fact employed for radical trifluoromethylation. Moreover, the reaction is extremely fast and the minimum reaction time is only ∼1 s. 相似文献
5.
Sano S Takehisa T Ogawa S Yokoyama K Nagao Y 《Chemical & pharmaceutical bulletin》2002,50(9):1300-1302
Tetrasubstituted (Z)-alkenes were readily prepared through the Horner-Wadsworth-Emmons reactions of methyl 2-[bis(2,2,2-trifluoroethyl)phosphono]propionate with aryl alkyl ketones by employing Sn(OSO(2)CF(3))(2) and N-ethylpiperidine. 相似文献
6.
Kashiwada Y Chiyo J Ikeshiro Y Nagao T Okabe H Cosentino LM Fowke K Morris-Natschke SL Lee KH 《Chemical & pharmaceutical bulletin》2000,48(9):1387-1390
3-Alkylamido-3-deoxy-betulinic acids were synthesized and evaluated for anti-HIV activity as part of the structure-activity relationship study of the potent anti-HIV agent 3-O-(3',3'-dimethyl)-succinyl-betulinic acid (DSB) (2). 3Alpha-diglycorylamide-3-deoxy-betulinic acid demonstrated relatively potent anti-HIV activity (EC50 0.24 microm, TI 728). However, replacing the ester group at C-3 in 2 and its analogues with an amido group yielded inactive or much less potent compounds against HIV replication, indicating that the ester group at C-3 in 2-4 is essential for potent anti-HIV activity. 相似文献
7.
Ken-ichi Sato Shoji Akai Akira Yoshitomo Yoshimitsu Takai 《Tetrahedron letters》2004,45(44):8199-8201
The merits of an indirect protecting method for hydroxyl groups using allyl groups via allyloxycarbonyl groups in the synthesis of antennary β-d-mannopyranosyl disaccharides from β-d-galactopyranosyl disaccharides were studied. Regioselective allyloxycarbonylation and conversion reactions involving simultaneous double SN2 nucleophilic substitution at C-2′ and C-4′ of benzyl O-[β-d-galactopyranosyl]-(1-4)-3,6-di-O-benzyl-2-deoxy-2-N-phthalimido-β-d-glucopyranoside were examined for comparison with the direct allylation method. The required β-d-mannopyranosyl disaccharide having proper protecting groups was obtained using this indirect method in 52% yield. In contrast, the reported direct allylation method using methyl O-(β-d-galactopyranosyl) disaccharide gave the corresponding β-d-mannopyranosyl disaccharide in only 7.5% yield. 相似文献
8.
Ishii K Itoya H Miwa H Fujitsuka M Ito O Kobayashi N 《The journal of physical chemistry. A》2005,109(26):5781-5787
We have investigated the excited-state properties and singlet oxygen ((1)Delta(g)) generation mechanism in phthalocyanines (4M; M = H(2), Mg, or Zn) and in low-symmetry metal-free, magnesium, and zinc tetraazaporphyrins (TAPs), that is, monobenzo-substituted (1M), adjacently dibenzo-substituted (2AdM), oppositely dibenzo-substituted (2OpM), and tribenzo-substituted (3M) TAP derivatives, whose pi conjugated systems were altered by fusing benzo rings. The S(1)(x) and S(1)(y) states (these lowest excited singlet states are degenerate in D(4)(h) symmetry) split in the low-symmetry TAP derivatives. The excited-state energies were quantitatively determined from the electronic absorption spectra. The lowest excited triplet (T(1)(x)) energies were also determined from phosphorescence spectra, while the second lowest excited triplet (T(1)(y)) states were evaluated by using the energy splitting between the T(1)(x) and T(1)(y) states previously reported (Miwa, H.; Ishii, K.; Kobayashi, N. Chem. Eur. J. 2004, 10, 4422-4435). The singlet oxygen quantum yields (Phi(Delta)) are strongly dependent on the pi conjugated system. In particular, while the Phi(Delta) value of 2AdH(2) is smallest in our system, that of 2OpH(2), an isomer of 2AdH(2), is larger than that of 4Zn, in contrast to the heavy atom effect. The relationship between the molecular structure and Phi(Delta) values can be transformed into a relationship between the S(1)(x) --> T(1)(y) intersystem crossing rate constant (k(ISC)) and the energy difference between the S(1)(x) and T(1)(y) states (DeltaE(S)(x)(T)(y)). In each of the Zn, Mg, and metal-free compounds, the Phi(Delta)/tau(F) values (tau(F): fluorescence lifetime), which are related to the k(ISC) values, are proportional to exp(-DeltaE(S)(x)(T)(y)), indicating that singlet oxygen ((1)Delta(g)) is produced via the T(1)(y) state and that the S(1)(x) --> T(1)(y) ISC process follows the energy-gap law. From the viewpoint of photodynamic therapy, our methodology, where the Phi(Delta) value can be controlled by changing the symmetry of pi conjugated systems without heavy elements, appears useful for preparing novel photosensitizers. 相似文献
9.
Yoshizawa M Nagao M Umemoto K Biradha K Fujita M Sakamoto S Yamaguchi K 《Chemical communications (Cambridge, England)》2003,(15):1808-1809
Despite their structural similarity, triangular tetradentate ligands 2b and 2c experience different assembly pathways on complexation with (en)Pd(NO3)2 to give M8L4 tetrahedral (3) and open cone (4) structures, respectively, due to steric restriction by side chains at the corner or on the edge of the ligands. 相似文献
10.
[reaction: see text] Highly basic lithium enolates are shown to be applicable to radical trifluoromethylation. The reaction is extremely fast, and the minimum reaction time is approximately 1 s. 相似文献