Synthesis of the Key Disaccharide of 3′-Sulfo Lewis X and Lewis A: The Novel E-Selectin Ligand

Benzyl 2,4,6-tri-O-benzyl-β-D-galactopyranoside (6) was synthesised from regioselective protection of stannylated benzyl 2,6-di-O-benzyl -β-D-galactopyranoside (3) with 4-methoxybenzyl chloride, followed by benzylation and oxidative removal of the temporary protecting group. The disaccharide (2) was prepared by condensation of the common acceptor 6 with 7 through thial activation as well as with 8 following Konigs Knorr procedure.     

Photostability of D–π–A nonlinear optical chromophores containing a benzothiazolium acceptor

For the practical application of second‐order NLO materials, not only a high molecular quadratic hyperpolarizability β but also good thermal, chemical, and photochemical stabilities are required. Most of the state‐of‐the‐art chromophores with high NLO response cannot be put to use because they are photochemically highly unstable. Good thermal and photochemical stabilities with preserved high hyperpolarizabilities can be achieved by replacement of an aromatic ring with easily delocalizable heteroaromatics, e.g., with benzothiazole. Furthermore, desirable modifications of the benzothiazole fragment lead to improvement in β values. Here we report results of a comprehensive investigation of the photochemical stability of seven D–π–A push–pull molecules based on a N‐methylbenzothiazolium acceptor and a N,N‐dimethylaminophenyl donor with a different length of conjugated bridge and different acceptor strength. The quantum yield (Φ) and the kinetic parameters of photoreactions were determined for existing photodegradation pathways on irradiation at 300–850 nm in MeOH. Trans–cis photoisomerization is proposed as a fast but inefficient photobleaching mechanism for these irradiation wavelengths. Self‐sensitized photooxidation by ¹O₂ makes very slow parallel photodegradation pathway and, albeit to small value of Φ, plays a dominant role in the photodegradation of the compounds investigated. Both structural modifications (extension of conjugated bridge and an additional acceptor group bonded to heterocycle) resulting in an increase of NLO response led to a decrease in photostability due to the self‐sensitized ¹O₂ photooxidative attack. Thus a compromise should be found between an increase in NLO response and a decrease in photostability to make a choice of studied compounds for practical applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical study on the isomerization mechanisms of phenylazopyridine on S0 and S1 states

In this work, some important structures tied closely to the isomerization of 2‐(phenylazo)pyridine (2‐PAPy) and 4‐(phenylazo)pyridine (4‐PAPy) on the S₀ and S₁ states were characterized in detail by using the complete active space SCF (CASSCF) theory. The isomerization mechanism was discussed on the basis of the mapped potential energy surfaces (PESs) and conical intersections (CIs). A comparison of PAPy with azobenzene was carried out to stress the effect of molecular structure on the photoisomerization details. The results indicate that the thermal isomerization for both 2‐PAPy and 4‐PAPy are mainly attributed to the inversion of CNN angle on the side of the pyridine ring. In view of the energy, an optimized CI_rot with a twisting structure supports the rotation mechanism in the photoisomerization of PAPy on the S₁ state. However, it was found that another conical intersection (CI_inv) with a planar structure is higher in energy than the corresponding trans‐FC structure, via which only the PAPy excited on S₂ state or vibrationally hot S₁ state can relax their excitation energy. Minimum energy paths (MEPs) showed that the relaxation process of cis‐PAPy being excited on the S₁ state is characterized by a smoothly falling curve, which is very similar to that of azobenzene. Furthermore, a S₁ minimum and a transition state (TS₁) were found to exist on the MEP starting from the trans‐FC point to the CI_rot for 4‐PAPy, but these two typical structures were not found on the MEP of 2‐PAPy. Compared with azobenzene, 4‐PAPy exhibits a very similar photoisomerization PES, but a subtly different one can be predicted in the case of 2‐PAPy. The present results are expected to provide useful information for the design of photoresponsive materials based on the PAPy units. Copyright © 2009 John Wiley & Sons, Ltd.     

Computational studies on amino-type excited-state intramolecular proton transfer and subsequent cis–trans isomerisation reactions of three 2-(2'-aminophenyl)benzothiazole derivatives

Excited-state intramolecular proton transfer (ESIPT) reactions of three amino-type 2-(2'-aminophenyl)benzothiazole (PBT-NH₂) derivatives, that is, 2-(2'-methylaminophenyl)benzothiazole (PBT-NHMe), 2-(2'-acetylaminophenyl)benzothiazole (PBT-NHAc) and 2-(2'-tosylaminophenyl)benzothiazole (PBT-NHTs), have been explored by the time-dependent density functional theory (TD-DFT) method with the B3LYP density functional. In addition, their absorption and fluorescence spectra were also simulated at the same theoretical level. The present studies reveal that the energy barriers of the first singlet excited state of the three titled compounds along the ESIPT reactions are predicted at 0.39, 0.30 and 0.12 eV, respectively, suggesting that the inclusion of a strong electron-withdrawing tosyl group can remarkably facilitate the occurrence of the ESIPT reaction, while the involvement of an electron-donating methyl group has no effect on the ESIPT process of the amino-type hydrogen-bonding system. Following the ESIPT, both PBT-NHAc and PBT-NHTs molecules can also undergo the cis–trans isomerisation reactions along the C₂–C₃ bond between benzothiazole and phenyl moieties, in which the energy barriers of the trans-tautomer → cis-tautomer isomerisations in both ground states are calculated at 0.33 and 0.27 eV, respectively. This implies that there may exist a long-lived trans-tautomer species in the ground states for PBT-NHAc and PBT-NHTs, as observed in the spectroscopic experiments of PBT-NHTs.     

Effect of pH and mobile phase additives on the chromatographic behaviour of an amide‐embedded stationary phase: Cyanocobalamin and its diaminemonochloro‐platinum(II) conjugate as a case study

Several mobile phase additives (i.e., organic acids and their ammonium salts) were used to modulate the chromatographic retention of cyanocobalamin and its cis‐diaminemonochloroplatinum(II) conjugate, depending on the specific nature of the stationary phase. Regardless of the mobile phase additive, the positively charged cyanocobalamin‐cis‐diaminemonochloroplatinum(II) conjugate was systematically less retained than cyanocobalamin on a conventional octadecyl‐silica column. In contrast, the amide‐embedded C18 column exhibited a progressive increase in the conjugate retention time upon changing the mobile phase additive from organic (acetic, formic and trifluoroacetic) acids to ammonium salts, ultimately leading to an inversion of the elution order. This change of retention was interpreted by invoking the interplay between hydrophobic interactions, hydrogen bonding between the conjugate and the polar amide groups and the ion‐pairing ability of the lyophilic counterions, whereby the acetate anion was found to be the most suitable to control the solute retention.     

Synthesis and Characterization of Phosphinecarboxamide and Phosphinecarbothioamide,and Their Complexation with Palladium(II) Complex

Reactions of isocyanates/isothiocyanates with primary and secondary phosphines without solvent at room temperature afforded phosphinecarboxamide/phosphinecarbothioamide, respectively, in excellent yields. Furthermore, palladium complex Pd(COD)Cl₂ was allowed to react with Ph₂PC(O)NHPh (1a) to afford [Pd{Ph₂PC(O)NHPh-κP}₂Cl₂] (3). On the other hand, the reaction of Pd(COD)Cl₂ with 1 eq. of Ph₂PC(S)NHPh (2a) afforded [PdCl₂{Ph₂PC(S)NHPh-κP,S}] (4). In the case of a 1:2 molar ratio, [PdCl{Ph₂PC(S)NHPh-κP,S}{Ph₂PC(S)NHPh-κP}]Cl (5) was formed. The newly obtained compounds were fully characterized using multielement NMR measurements and elemental analyses. In addition, the molecular structures of Ph₂PC(O)NH(CH₂)₂Cl (1j), Ph₂PC(S)NHPh(4-Cl) (2c), and 3–5 were determined using single-crystal X-ray diffraction.     

Synthesis,structure, and properties of poly[1‐(trimethylgermyl)‐1‐propyne]

Polymerization of 1‐(trimethylgermyl)‐1‐propyne (TMGP) with TaCl₅ and NbCl₅ produced a colorless polymer in high yields, whose molecular weight reached about 3 × 10⁵–14 × 10⁵. The molecular weight distribution of the poly(TMGP) with NbCl₅ in cyclohexane was somewhat narrow (M_w /M_n = ∼1.54). The TaCl₅‐based poly(TMGP) dissolved in toluene, chloroform, cyclohexane, carbon disulfide, carbon tetrachloride, tetrahydrofuran, hexane, and so forth; the NbCl₅‐based polymer was less soluble and did not dissolve in hexane, despite its lower molecular weight. The cis contents of the NbCl₅‐ and TaCl₅‐based poly(TMGP)s determined by ¹³C NMR were 67 ± 5 and 28 ± 3%, respectively. The onset temperature of the weight loss of poly(TMGP) in air was 350 °C, indicating fair thermal stability. The oxygen permeability coefficient (P) of poly(TMGP) at 25 °C was 7800 barrer after the methanol conditioning, and the permeability was fairly stable to aging. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2964–2969, 2000     

Substituent effect of the ester moiety of epoxysuccinates on the polycondensation with diamine

Di‐2,2,2‐trichloroethyl cis‐epoxysuccinate, di‐2‐cyanoethyl cis‐epoxysuccinate, and di‐2‐methoxyethyl cis‐epoxysuccinate were synthesized, and the substituent effect of the epoxysuccinates on the polycondensation with diamine was studied. The order of reactivities of the epoxysuccinates with m‐xylylenediamine was as follows: di‐trichloroethyl ester ≫ di‐cyanoethyl ester > di‐methoxyethyl ester, such was also confirmed by the model reaction of the epoxysuccinate with benzylamine. ¹H NMR and IR spectroscopic study and ab initio calculation also well explained the reactivity order. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 504–508, 2000     

(4R-cis)-6-[2-[2-(4-氟苯基)-5-(1-异丙基)-3-苯基-4-[苯胺(羰基)]-1 H-吡咯-1-基]乙基]-2,2-二甲基-1,3-二氧己环-4-乙酸叔丁酯的波谱学研究

对(4R-cis)-6-[2-[2-(4-氟苯基)-5-(1-异丙基)-3-苯基-4-[苯胺(羰基)]-^1H-吡咯-1-基]乙基]-2,2-二甲基-1,3-二氧己环-4-乙酸叔丁酯的傅里叶变换离子回旋共振质谱(FT-ICR-MS)、核磁共振氢谱(^1H-NMR)、碳谱(^13C-NMR)以及^1H同核位移相关谱(^1H-^1HCOSY)、检出^1H的异核多量子相干谱(HMQC)和^1H检测的异核多键相关谱(HMBC)报道并进行解析。确定了^1H谱、^13C谱中各谱峰的归属,研究了其六元环部分的立体构象,并就空间效应对其化学位移的影响做了初步的探讨。