Studies Toward the Stereoselective Synthesis of C13 to C21 Fragment of the Brasilinolides Family of Immunosuppressive Macrolides

The work describes our attempts to synthesize the C13 to C21 fragment of brasilinolides, a 32-membered macrolide class of molecule. The C13 to C21 segment encompasses six asymmetric centers and a pyran ketal moiety. The synthesis starts from L-malic acid, and the salient features of our asymmetric synthesis are opening of epoxide, assymmetric dihydroxylation for the creation of vic-diol, and Barbier allylation.     

Titanium-Promoted Acylation of Sulfonamides to N-Acylsulfonamide PPARα Antagonists

The direct acylation of sulfonamides by esters represents an attractive strategy in organic chemistry, being an interesting alternative to classical approaches to N-acylsulfonamides. Here is described a simple and effective method to obtain N-acylsulfonamides of pharmaceutical interest, in a reaction promoted by titanium(IV) chloride. This strategy was successfully applied to the synthesis of a peroxisome proliferator–activated receptor α antagonist with a benzenesulfonimide moiety, ensuring an excellent yield of product. The reaction was further studied to explore the behavior of different α-bromoesters and esters and the effects of para-substitution in the benzenesulfonamide moiety.     

Zinc-Mediated Tandem-One-Pot Facile Synthesis of 1-(Arylsulfonyl) Aryl/Heteryl Methanes: A Case of C‒S Bond Formation

Reaction of arylmethyl/heteryl methyl zinc chloride (generated in situ from aryl methyl and heteryl methyl chloride and zinc metal) with aryl sulfonyl chlorides in tetrahydrofuran (THF) under mild conditions (i.e., at room temperature) furnishes the corresponding 1-(aryl sulfonyl)aryl/heteryl methanes in good yields.

Simple and Efficient System for the α-Bromination of a β-Ketoester by Using N-Bromosuccinimide in the Presence of Silica-Supported NaHCO3 as the Heterogeneous Catalyst: An Environmentally Benevolent Approach

Selective and efficient α-bromination of β-ketoesters and cyclic and acyclic ketones is achieved by reaction with N-bromosuccinimide (NBS) catalyzed by silica-supported sodium bicarbonate (NaHCO₃ · SiO₂) under mild reaction conditions and with short reaction times. With 100% selectivity with all substrates, after 45 min at room temperature (20 ± 2 °C), conversions for ethylacetoacetate were 67% and for acetophenone, cyclohexanone, and cycloheptanone were 58, 50, and 55%, respectively. Acetyl acetone recorded 65% conversion with 100% selectivity. Although cyclopentanone and toluene had only 20% conversion, both reactions showed 100% selectivity toward α-bromination. The catalysts exhibit activity and reusability.     

Synthesis, Structure and Thermochromic Properties of a Copper(Ⅱ) Complex Based on Naphthyl Carboxylate and Benzimidazolyl Ligands

One novel copper(Ⅱ) complex, [Cu(NAA)2(bim)2]·H2O (1, HNAA = a-naphthylacetic acid, bim = benzimidazole) has been synthesized and characterized by X-ray single-crystal diffraction analysis, elemental analysis, and IR spectrum. It crystallizes in monoclinic, space group C2/c with a = 1.15969(12), b = 1.9757(2), c = 1.45763(16) nm, β = 104.712(2)°, V = 3.2298(6) nm3, Z = 4, C38H32N4O5Cu, Mr = 688.22, Dc = 1.418 g/cm-3, μ = 0.729 mm-1, S = 1.039, F(000) = 1428, the final R = 0.0380 and wR = 0.0912 for 2849 unique reflections. In 1, two carboxylate and two benzimidazole ligands coordinate to the central Cu(Ⅱ) atom by a bidentate chelate mode. Interesting, reversible thermochromic properties of 1 can be observed and investigated by thermal analysis method.     

On the necessity of organic solvent extraction for carbon isotopic analysis of α-cellulose: implications for environmental reconstructions

α-cellulose is widely used as a target substance for isotope ratio analysis in environmental reconstructions. Its preparation includes three basic steps: organic solvent extraction, delignification and alkaline hydrolysis. Recent works have suggested omission of the first step. We have made a detailed comparison in carbon isotope ratio of α-cellulose with or without organic solvent extraction using 32 consecutive tree ring and 30 subfossil peat samples. These samples were exposed to three different chemical treatments: with organic solvent extraction as the first step (Cell_OE), without organic solvent extraction (Cell_NOE), and with organic solvent extraction as the final step (Cell_NOE/OE). The third treatment is used to test if organic extractives can be completely removed or if their solubility in organic solvents has been altered by delignification and alkaline hydrolysis. In tree rings and peat, δ¹³C_{C ell NOE} was always significantly different from δ¹³C_{C ell OE}, but the trends were not the same. In tree rings, δ¹³C_{C ell NOE} was always more negative than δ¹³C_{C ell OE} by ?0.31 ～ ?0.01‰. In contrast, δ¹³C_{C ell NOE} in peat could be more negative or more positive than δ¹³C_{C ell OE} by ?3.08 ～ 0.27‰. The third chemical treatment resulted in different patterns. For tree rings, δ¹³C_{C ell NOE/OE} was still more negative than δ¹³C_{C ell OE} by ?0.36 ～ ?0.08‰. However, the differences between δ¹³C_{C ell NOE/OE} and δ¹³C_{C ell OE} for peat varied in a more narrow range from ?0.58 to 0.61‰, compared to the differences between δ¹³C_{C ell NOE} and δ¹³C_{C ell OE}. These results exposed a complex chemical evolution behaviour and an incomplete removal of lipids during delignification and alkaline hydrolysis. The mean value, long-term trend and seesaw patterns for a tree ring or peat Cell_NOE series were significantly different from those for a Cell_OE series, indicating that omission of organic solvent extraction will lead to a biased inference of past environmental conditions.     

Synthesis and Enzyme Inhibitory Activities of Highly Functionalized Pyridylmethyl-C-β-D-Glycosides

Several pyridylmethyl-C-β-D-glycosides (3a–3l, 6a, and 6h) were synthesized by refluxing 3-(β-D-glucopyranosyl)/(β-D-cellobiosyl)-propanones and dicyanobenzylidenes with ammonium acetate in anhydrous toluene in moderate to good yields. The reaction involves a C?C Michael addition of enamine, formed from glycosyl ketone and ammonium acetate, to the dicayanobenzylidene derivative; subsequent dehydrative cyclization; and oxidative aromatization. Two of these prototypes, compounds 3e and 3k, were deacetylated to the respective glucopyranosyl methyl pyridines 4e and 4k with NaOMe/MeOH. The synthesized compounds were screened for their in vitro α-glucosidase inhibitory activities and one of the compounds showed 20% inhibition as compared to standard drug acarbose displaying 39% inhibition.     

New amino acid based biodegradable poly(ester amide)s via bis-azlactone chemistry

Abstract

Three new classes of the amino acid based biodegradable (AABB) polymers were synthesized via step growth polymerization of bis-azlactones and amino acid based diamine-diesters with activated fatty diester and alkylenediamine: a) poly(ester amide)s (PEAs) were obtained by polymerization of bis-azlactones with diamine-diesters, b) hydrophobically modified co-poly(ester amide)s (co-PEAs) were synthesized by copolymerization of activated fatty diacid diester and bis-azlactones with diamine-diesters, and c) poly(ester amide-co-amide)s (PEA-co-PAs) were obtained by copolymerization of alkylene diamine and diamine-diesters with bis-azlactones. The new poly(ester amide)s showed relatively low-molecular-weights (M_w within 2,800–19,600?Da, GPC in DMF), whereas the new co-poly(ester amide)s and poly(ester amide-co-amide)s exhibited high-molecular-weights (M_w within 40–100?kDa) leading to good mechanical properties. Incorporation of the bis-azlactone fragments into the poly(ester amide)s backbone increased hydrophobicity and thermal stability, whereas incorporation of diamine-diester units into the backbone of the bis-azlactone based polyamides rendered them biodegradable. Synthesized AABB polymers are potential candidates for constructing resorbable surgical and pharmaceutical devices.     

Atom Transfer Radical Polymerization of Methyl Methacrylate with α,α,α′,α′‐Tetrachloroxylene as an Initiator

The homogeneous ATRP of methyl methacrylate (MMA) using α,α,α′,α′‐tetrachloroxylene (TCX)/CuCl/N,N,N′,N″,N″–pentamethyldiethylenetriamine (PMDETA) as the initiating system has been successfully carried out. The kinetic plots showed first order relationship vs. monomer concentration. Well‐controlled polymerizations with low polydispersities (M_w/M_n=1.15?1.25) polymers have been achieved. The molecular weights increased linearly with monomer conversions and were close to the theoretical values, indicating high initiation efficiency. The polymerization rate increased significantly with an increase of TCX concentration. The rate of polymerization was about 0.6 orders with respect to the concentration of initiator. The polymerization rate increased significantly with an increase of CuCl concentration. The dependence of ln k_p ^app on ln ([CuCl]₀) indicated a 0.91 order. The apparent activation energy was calculated ΔE_app ^≠=43.3 KJ/mol, and the enthalpy of the equilibrium, ΔH_eq ⁰, was estimated to be 21.1 KJ/mol. The structure of obtained PMMA was analyzed by means of ¹H NMR spectroscopy. The result proved that the TCX acted as a bifunctional initiator for ATRP of MMA.