Context-free grammars for triangular arrays

We consider context-free grammars of the form G = {f → fb1+b2+1ga1+a2, g → fb1 ga1+1},where ai and bi are integers sub ject to certain positivity conditions. Such a grammar G gives rise to triangular arrays {T(n, k)}0≤k≤n satisfying a three-term recurrence relation. Many combinatorial sequences can be generated in this way. Let Tn (x) =∑nk=0T(n, k)xk. Based on the differential operator with respect to G, we define a sequence of linear operators Pn such that Tn+1(x) = Pn(Tn(x)). Applying the characterization of real stability preserving linear operators on the multivariate polynomials due to Borcea and Br?ndén, we obtain a necessary and sufficient condition for the operator Pn to be real stability preserving for any n. As a consequence, we are led to a sufficient condition for the real-rootedness of the polynomials defined by certain triangular arrays, obtained by Wang and Yeh.Moreover, as special cases we obtain grammars that lead to identities involving the Whitney numbers and the Bessel numbers.     

A silver(I)-catalyzed reaction of 2-alkynylbenzaldoxime with arylsulfonyl chloride

A silver-catalyzed reaction of 2-alkynylbenzaldoxime with arylsulfonyl chloride proceeds smoothly at room temperature to afford 4-tosyloxyisoquinolines in moderate to good yields. Additionally, the resulting 4-tosyloxyisoquinolines could be further elaborated through palladium-catalyzed coupling reactions leading to diverse isoquinolines.     

Efficient synthesis of functionalized 6-substituted-thiosalicylates via microwave-promoted Suzuki cross-coupling reaction

Functionalized 6-substituted-thiosalicylates are key intermediates for the synthesis of pyrimidinyl(thio)salicylic acids, a group of important herbicides targeting plant acetohydroxyacid synthase. Therefore, it is of great interest to develop an efficient method for the syntheses of 6-substituted-thiosalicylates. Herein, we have developed a direct and efficient method for the synthesis of functionalized 6-substituted-thiosalicylates (4) from aryl iodide (1) by using an improved microwave-assisted Suzuki cross-coupling reaction. Almost all the reactions proceeded smoothly and afforded moderate to excellent yields of products. Moreover, this protocol is obviously superior to the traditional available methods and could be utilized to synthesize pyrimidinyl(thio)salicylic acid and its derivatives.     

Highly selective trifluoroacetic ester/ketone metathesis: an efficient approach to trifluoromethyl ketones and esters

A highly selective and atom efficient ‘trifluoroacetic ester/ketone metathesis’ has been sincerely witnessed. Enolizable alkyl (at least two non-hydrogen atoms) aryl ketones were found to react readily with ethyl trifluoroacetate under the promotion of NaH to afford trifluoroacetic ester/ketone exchange products, trifluoromethyl ketones (TFMKs), and aromatic acid esters, which were quite different from the general Claisen condensation products, 1,3-diketones. The outcome of the reaction between ketone and ethyl trifluoroacetate is strongly related to the structures of substrates, the steric congestion caused by alkyl group is in favor of the C–C bond cleavage. DFT investigation further disclosed that the metathesis reaction was a kinetically favored pathway. Using only a slight excess of cheap trifluoromethylation reagent, simple operation and mild conditions make it a practical method for preparation of TFMKs on large scale, as well as a new choice of converting aryl alkyl ketones to aromatic acid esters.     

Metal-free oxidative arylphosphination of activated N-substituted-N-arylacrylamide derivatives using K2S2O8

A novel metal-free oxidative arylphosphination of activated N-substituted-N-arylacrylamide derivatives by phosphorylation and C–H functionalization cascade process has been developed. This methodology provides an efficient way to construct a variety of phosphorus-containing oxindole moieties.     

Total synthesis of fuzinoside

The first total syntheses of fuzinoside (1b) were achieved from d-galactose through two strategies (BCA and ABC) in 11 (total yield: 5.0%) and 15 (total yield: 3.7%) steps, respectively. Comparison of NMR data of synthetic compound 1b and those of the fuzinoside isolated from the lateral roots of Aconitum carmicaelii suggests that the structure reported in the literature ^1 and 2 might not be accurate. The synthetic fuzinoside (1b) exhibited moderate cardiac activity in the isolated bullfrog heart assay.     

Design,synthesis and anti-influenza virus activities of terminal modified antisense oligonucleotides

Four novel terminal modified antisense oligonucleotides (ODNs) were designed, synthesized and tested for their anti-influenza virus activity. Initial biological studies indicated that lipophilic and rimantadin emodificated Flutide exhibited more potent anti-H1N1 activity than Flutide. Among them, lipophilic modificated ODN (Flutide-I) showed the most antiviral activity. The EC₅₀ value of Flutide-I for inhibiting H1N1 induced cytopathic effect (CPE) and H1N1 RNA were respectively (0.26 ± 0.16) μM and (0.11 ± 0.03) μM. The cytotoxicity of these compounds has also been assessed. No significant cytotoxicities were found for any of these compounds with the concentrations up to 20 μM.     

Suzuki–Miyaura cross-coupling reaction of 1,2-oxaborol-2(5H)-ols with carboxylic anhydrides: a new method to furans

An efficient one-step method has been developed to construct furans via a Suzuki–Miyaura cross-coupling reaction of 1,2-oxaborol-2(5H)-ols with carboxylic anhydrides. In the presence of Pd(OAc)₂/PCy₃, the multi-substituted alkenylboron compounds could couple with anhydrides to obtain furans in moderate-to-good yields. The addition of bases promoted the coupling reaction, and the plausible reaction mechanism was proposed.     

Alstolactines A–C,novel monoterpenoid indole alkaloids from Alstonia scholaris

Three novel ring-fused monoterpenoid indole alkaloids, alstolactines A–C (1–3), were isolated from the long-term stored leaves of Alstonia scholaris. Their structures were identified on the basis of extensive spectroscopic data and X-ray diffractions. Moreover, the absolute configurations of these related structures were indicated by the crystal X-ray diffractions (Mo Kα) of 1a, a chlorinated derivative of 1.