Beckmann rearrangement of cyclotriveratrylene (CTV) oxime: tandem Beckmann-electrophilic aromatic addition

The Beckmann rearrangement has been performed on the oxime of cyclotriveratrylene (CTV) with thionyl chloride affording the ring-expanded 10-membered ring amide exclusively in high yield. Modified conditions afford a helical pentacycle derived from an unusual tandem Beckmann rearrangement and electrophilic aromatic addition followed by demethylation and tautomerization.     

Hydrogelators of cyclotriveratrylene derivatives

Developing cavity-based supramolecular hydrogels is in its infancy because not many such hydrogelators are available. Reported herein is our creation of rigid cavitand cyclotriveratrylene (CTV) based hydrogelators from the molecular backbones of CTVs that were in limited cases shown to form organogels. For doing so deprotonable -COOH or protonable -NH(2) was introduced as terminal group into the rigid and hydrophobic CTV backbones. We thus successfully obtained optically anisotropic supramolecular hydrogels from these new CTVs hydrogelators with excellent thermostability and high tolerance towards strong electrolytes. The obtained CTV-1 and CTV-2 hydrogels are luminescent and exhibit reversible gel-to-sol and sol-to-gel transitions upon pH variations. The success in creating CTV-1 and CTV-2 hydrogelators on the basis of the skeleton of a CTV-organogelator suggests that balancing the hydrophilic and hydrophobic characters of the ionic and hydrophobic moieties well in the gelator molecule is important for designing a promising hydrogelator.     

Isolation of the saddle and crown conformers of cyclotriveratrylene (CTV) oxime

The oxime of cyclotriveratrylene (CTV) has been prepared and the individual crown and saddle conformers were isolated and characterized. The equilibrium constant was measured in CDCl₃ and in DMSO-d₆ and was shown to favor the crown conformer by an order of magnitude in DMSO-d₆, relative to an approximately equal mixture at equilibrium in CDCl₃. The time course for interconversion of the saddle to the crown was measured by ¹H NMR and the t_1/2 of the saddle was determined to be 2.45 h in CDCl₃ at 25 °C, and 3.71 h in DMSO-d₆.     

A new flexible strategy for the synthesis of gem-difluoro-bisarylic derivatives and heterocyclic analogues

A new strategy has been designed for the preparation of gem-difluoro-bisarylic derivatives. It starts from easily accessible and reactive gem-difluoro-propargylic intermediates and elaborates the aromatic rings by a Diels-Alder-aromatization sequence. Heterocyclic systems can be also obtained by 1,3 dipolar cycloadditions, affording mixed aromatic/heteroaromatic derivatives with CF₂ as a linker. Since this motif is a bioisostere of O and CO, corresponding bisarylic scaffolds could be of use to prepare chemical libraries of fluorinated analogues of bioactive natural products and/or drugs.     

Sugar-functionalized water-soluble cyclotriveratrylene derivatives: preparation and interaction with fullerene

Cyclotriveratrylene (CTV) has attracted much attention because of its good chemical stability, small cavity, stable conformation, and facile modification. In this article, two water-soluble CTV derivatives (CTV-G and CTV-L) functionalized by glucose and lactose residues were synthesized, respectively. Unexpectedly, sugar-bearing CTVs exhibit a distinct photoluminescence, which might be ascribed to the enhanced planar conformation of cyclotriveratrylene ring derived from the spatial effect of bulky branch groups. The interaction between the water-soluble CTV derivatives and C(60) was investigated in organic solvent and aqueous solution, which was further characterized by fluorescence spectra, ultraviolet-visible spectra, and Raman spectra. CTV-G can associate with C(60) to form supramolecular complex with 1:1 molar ratio (K(a) = 1.38 × 10(5) M(-1), 298 K). As for CTV-L, a similar complex with a lower association constant (K(a) = 5.09 × 10(4) M(-1), 298 K) can also be formed.     

A new strategy for the synthesis of β-benzylmercaptoethylamine derivatives

Here, we describe a new experimental approach to the synthesis of the β-benzylmercaptoethylamine functionality, and illustrate its synthetic utility in multi-component reactions. Although prevalent in modern organic synthesis, no general methods have been described for this functionality. Using a carefully developed LiOH-water-ethanol reaction mixture, we were able to produce a diverse collection of β-benzylmercaptoethylamines containing a range of sensitive functional groups in excellent yields. To further illustrate their utility in molecular library synthesis, we also report the use of β-benzylmercaptoethylamines in five different multi-component reactions.     

Synthesis of new boron complexes: application to transfer hydrogenation of acetophenone derivatives

Two new boron complexes were synthesized from N‐[3‐(methylmercapto)aniline]‐3,5‐di‐tert‐butylsalicylaldimine ( LH ) with boron reagent BPh₃ or BF₃.Et₂O. These boron complexes are stable and easily soluble in protic solvents such as ethanol (C₂H₅OH) but hardly soluble in nonprotic solvents such as chloroform (CHCl₃), dichloromethane (CH₂Cl₂) and tetrahydrofuran (THF). All new boron complexes have been fully characterized by both analytical and spectroscopic methods. The catalytic activities of complexes [LBPh₂], 2 , and [LBF₂], 3 , in the transfer hydrogenation of acetophenone derivatives were tested. Stable boron complexes were found to be efficient catalysts in the transfer hydrogenation of aromatic ketones in good conversions up to 99% in the presence of iso‐PrOH/KOH. Copyright © 2011 John Wiley & Sons, Ltd.     

Immune complexes in blood: a new strategy for the analysis of their antigen portion.

A method is described for the characterization of protein antigens from circulating immune complexes from plasma. Free immunoglobulins G were separated from larger immune complexes by gel filtration with a fast protein liquid chromatographic system. The collected immune complexes were dissociated with 4M urea into antigens and antibodies. With a second column run with 4M urea, antigens smaller than 120 kDa were separated from unloaded antibody fractions. After concentration, they were analyzed by two-dimensional gel electrophoresis.     

A new strategy for the stereoselective synthesis of 2,3-dideoxy-3-fluoro-D-ribofuranose derivatives

The important intermediate for syntheses of various anti-HIV nucleoside analogues, methyl 2,3-dideoxy-3-fluoro-6-O-(p-methylbenzoyl)-a-D-ribofuranoside, was synthesized starting from 2-deoxy-D-ribose in 5 steps with an overall yield of 24%. This strategy can be also used for synthesizing other analogues with various substitutions at 3-C position.     

Sulfur-incorporating cyclotriveratrylene analogues: the synthesis of cyclotrithioguaiacylene

Cyclotriguaiacylene 1 is the universal precursor of cryptophanes, and represents an important intermediate for the preparation of functionalized cavitands of the cyclotriveratrylene family. Its thio analogue (cyclotrithioguaiacylene 3) was synthesized by two different routes, involving either the Newman-Kwart or the Pummerer rearrangement. The latter, performed starting from a trisulfoxide precursor, produced a purer compound in higher overall yield.     

Improved syntheses of bis(beta-cyclodextrin) derivatives, new carriers for gadolinium complexes

In the last decade a number of reports have been published on the synthesis and characterization of bridged cyclodextrin dimers (bis-CDs) connected with linkers of different lengths and structures. These dimers, having two hydrophobic cavities in close proximity, display much higher binding affinities and molecular selectivities than parent CDs, forming stable supramolecular adducts. We describe new synthetic protocols for the preparation of bis(beta-CDs) bearing 2-2', 3-3' and 6-6' bridges. Some of the critical steps were carried out either under high-intensity ultrasound (US) or microwave (MW) irradiation. Bis(beta-CDs) containing 6-6' ureido- and thioureido-bridges were prepared in high yields by a MW-promoted aza-Wittig reaction using polymer-bound triphenylphosphine, while those containing 2,2' and 3,3' bridges were prepared from mono-alkenyl beta-CDs by the cross-metathesis reaction (homodimerization) in the presence of 2(nd)-generation Grubbs catalyst under sonochemical conditions. By these improved protocols CD dimers could be obtained in gram amounts to prepare stable adducts of bis-CDs with contrast agents (CAs) containing gadolinium(iii) chelates. In the case of Gd(iii) chleate "G-1" the inclusion complexes were found to be 2 to 3 orders of magnitude more stable than that formed by beta-CD (K(ass) = 4.3 x 10(4) M(-1)vs 8.0 x 10(2) M(-1)). Relaxivity increased as well by factors of 3 and 4, viz. from 9.1 mM(-1) s(-1) (beta-CD) to 27.7 and 35 mM(-1) s(-1).     

A new strategy for the synthesis of 2-mercaptobenzazole derivatives by green chemistry metrics

Abstract

A green and efficient method has been developed for the synthesis of 2-mercaptobenzazole derivatives via the reaction of commercially available aniline derivatives with low-cost and nontoxic potassium thiocyanate in water. The reactions proceeded smoothly under catalyst- and ligand-free conditions to give the corresponding products in good to excellent yields. The versatility, low cost, and environmental friendliness, in combination with high yields and easy work-up makes the procedure noteworthy.     

Facile preparation of new unsymmetrical curcumin derivatives by solid-phase synthesis strategy

Seventeen unsymmetrical curcumin derivatives were synthesized in good yield and purity by a facile solid phase synthesis strategy.     

A flexible strategy for the divergent modification of pleuromutilin

The complex antibacterial natural product, pleuromutilin, can be directly modified by the radical addition reaction of various xanthates to the unactivated terminal olefin present on C-12.     

A new eco-friendly strategy for the synthesis of novel antimicrobial spiro-oxindole derivatives via supramolecular catalysis

Novel spiro-oxindole derivatives were synthesised by one-pot multicomponent reaction using isatins, urea and 1,3-dicarbonyls. β-Cyclodextrin, an oligosaccharide, catalysed the reaction and can be reused for further reaction after recovery. This developed synthetic route is environmentally benign in which water is used as solvent to produce excellent yields of products. The synthesised compounds were evaluated for their antimicrobial activities against two bacteria and two fungi. All the synthesised spiro-oxindoles exhibit significant antimicrobial activity.     

A new strategy for asymmetric synthesis of aminophosphonic acid derivatives: the first enantioselective catalytic reduction of C-phosphorylated imines

The first highly enantioselective catalytic reduction of 1-imino-2,2,2-trifluoroethylphosphonates and the synthesis of enantiomerically enriched biorelevant phosphonotrifluoroalanine is reported.     

Ruthenium complexes containing bis-benzimidazole derivatives as a new class of apoptosis inducers

A series of ruthenium complexes containing bis-benzimidazole derivatives have been synthesized and identified as able to target mitochondria and induce caspase-dependent apoptosis in cancer cells through superoxide overproduction.     

Infrared spectra of new Re(III) complexes with thiourea derivatives

Complexes of the type [Re(III)L6]X3, with L = thiourea, N-methylthiourea, N-ethylthiourea or N,N'-dimethytlthiourea and X = Cl- or PF6-, were prepared as suitable precursors for the synthesis of new rhenium complexes potentially useful in nuclear medicine. The infrared (IR) spectra of these complexes were recorded and analyzed and a general vibrational pattern for Re(III) complexes with thiourea derivatives could be established. Approximate assignments for N-allylthiourea and N-ethylthiourea are also proposed for the first time. The synthesis of the new complex [Re(III)(N-allylthiourea)6](PF6)3 is also reported, and information about its structural characteristics was obtained comparing its IR spectrum with those of the other complexes of the investigated series.     

Metal complexes of anthranilic acid derivatives: A new class of noncompetitive α-glucosidase inhibitors

Metal complexes of anthranilic acid derivatives that constitute a novel class of non-sugar-type aglucosidase inhibitors were synthesized and assessed in vitro for inhibitory activity. All of the Ag(I)complexes(9–16) inhibited a-glucosidase at the nanomolar scale, while 3,5-dichloroanthranilic acid silver(I)(9) was the most potent(IC_(50)= 3.21 nmol/L). Analysis of the kinetics of enzyme inhibition indicated that the mechanism of the newly prepared silver complexes was noncompetitive. The structure-activity relationships were also analyzed, and they are discussed in this report.