A catalytic one-step process for the chemo- and regioselective acylation of monosaccharides

An organocatalytic method for the chemo- and regioselective acylation of monosaccharides has been developed. Treatment of octyl beta-D-glucopyranoside with isobutyric anhydride in the presence of 10 mol % of a C2-symmetric chiral 4-pyrrolidinopyridine catalyst (1) at -50 degrees C gave the 4-O-isobutyryl derivative as the sole product in 98% yield. Thus, chemoselective acylation, favoring a secondary hydroxyl group in the presence of a free primary hydroxyl group, and regioselective acylation, favoring one of three secondary hydroxyl groups, took place with perfect selectivity. A competitive acylation between octyl beta-D-glucopyranoside and a primary alcohol (2-phenylethanol) with 1.1 equiv of isobutyric anhydride in the presence of 1 gave the 4-O-isobutyrate of octyl beta-D-glucopyranoside with 99% regioselectivity in 98% yield, which indicates that acylation of the secondary hydroxyl group at C(4) of the carbohydrate proceeds in an accelerative manner. A possible mechanism, involving multiple hydrogen-bonding between 1 and the monosaccharide, is proposed for the chemo- and regioselective acylation.     

Fabrication of a nano-biocatalyst for regioselective acylation of arbutin

A nano-biocatalyst has been successfully prepared via coordination between zinc ion and the nitrogen atoms of the amide groups in the Candida sp. 99-125 lipase. The as-prepared nanoparticle has an excellent hierarchical structure with a large number of separate petals. In regioselective acylation of arbutin, the nano-biocatalyst showed enhanced enzyme activities to about 4.3-folds than the free enzyme. Meanwhile, the prepared nano-biocatalyst exhibited good operational reusability and only about 6% of enzyme activity has lost during 10 continuous reaction-recycles.     

1-acetoxyvinyl phosphonates: Facile synthesis via catalytic acylation of dialkyl phosphites

A new and facile method of synthesis of 1-acetoxyvinyl phosphonates ( 2 ) has been found. Dialkyl phosphites react readily with acetic anhydride in acetonitrile solution in the presence of catalysts to produce 2 and acylphosphonates ( 1 ) as a minor product. The most efficient catalysts are metal compounds of variable valency: iron(II), iron(III), and cobalt(II) chlorides. The same compounds catalyze transformation of 1 into 2 in an acetonitrile solution of acetic anhydride.     

Total synthesis of diptoindonesin G via a highly efficient domino cyclodehydration/intramolecular Friedel-Crafts acylation/regioselective demethylation sequence

A highly efficient total synthesis of diptoindonesin G is described employing a domino dehydrative cyclization/intramolecular Friedel-Crafts acylation/regioselective demethylation reaction of aryloxyketone 7 by the action of BCl(3) wherein the tetracyclic 6H-anthra[1,9-bc]furan-6-one skeleton was constructed via the 3-arylbenzofuran in a one-pot manner. This is the first example of the strategic combination of these three reactions in a cascade fashion. The routes presented here allow for direct access to diptoindonesin G and its analogues.     

A sulfoxide-promoted, catalytic method for the regioselective synthesis of allylic acetates from monosubstituted olefins via C-H oxidation

Sulfoxide ligation to Pd(II) salts is shown to selectively promote C-H oxidation versus Wacker oxidation chemistry and to control the regioselectivity in the C-H oxidation products. A catalytic method for the direct C-H oxidation of monosubstituted olefins to linear (E)-allylic acetates in high regio- and stereoselectivities and preparatively useful yields is described. The method using benzoquinone as the stoichiometric oxidant and 10 mol % of Pd(OAc)2 or Pd(O2CCF3)2 as the catalyst in a DMSO/AcOH (1:1) solution was found to be compatible with a wide range of functionality (e.g., amides, carbamates, esters, and ethers, see Table 2). Addition of DMSO was found to be critical for promoting the C-H oxidation pathway, with AcOH alone or in combination with a diverse range of dielectric media, leading to mixtures favoring Wacker-type oxidation products (Tables 1, S3). To explore the role of DMSO as a ligand, the bis-sulfoxide Pd(OAc)2 complex 1 was formed and found to be an effective C-H oxidation catalyst in the absence of DMSO (eqs 2, 3). Moreover, catalyst 1 effects a reversal of regioselectivity, favoring the formation of branched allylic acetates.     

A convenient method for the preparation of mono- and bis-substituted photochromic bis(benzothienyl)perfluorocyclopentenes via regioselective Friedel-Crafts acylation

The regioselective Friedel-Crafts acylation of 1,2-bis(2-methylbenzo[b]thien-3-yl)hexafluorocyclopentene was developed. Depending on the reaction conditions, mono- or bis(bromoacetyl) derivatives are formed as single products in good yields. Further heterocyclizations involving α-bromoketone moieties gave a series of new photochromic compounds.     

Cucurbituril-resisted acylation of the anti-tuberculosis drug isoniazid via a supramolecular strategy

A chemical investigation reveals that the resistance to acylation of an anti-tuberculosis drug, isoniazid is a consequent result of the inclusion or exclusion of cucurbit[n]urils (n = 6 or 7). The (1)H NMR spectra analysis shows that the different interaction models of the isoniazid with the two cucurbiturils are dependent on the cavity size of the hosts. Quantum chemistry calculations with density functional theory method indicate that the interaction of the isoniazid with both cucurbiturils is through thermodynamic stabilization in both the gas phase and aqueous solution through hydrogen bonding on the portal carbonyls of the cucurbiturils. Electronic absorption titration spectra suggest the hosts and guest interact in a ratio of 1 : 1 with moderate binding constants. Acylation kinetics of isoniazid with various acylating agents in the presence of the cucurbiturils revealed that resistance is only dependent on the host-isoniazid ratio, and independent on the size of the cucurbiturils and the species of acylating agents.     

Synthesis, characterization, and catalytic reactivity of a highly basic macrotricyclic aminopyridine

The synthesis methods, physicochemical and structural characteristics, and catalytic reactivity of new macrocyclic proton chelators, N,N',N'-tris(p-tolyl)azacalix[3](2,6)(4-pyrrolidinopyridine) and N,N',N'-tris(p-tolyl)azacalix[3](2,6)(4-piperidinopyridine), are studied. The introduction of pyrrolidino and piperidino groups into the pyridine unit enables the enhancement of the synergistic proton affinity of the cavity of the macrotricycle giving a high basicity (pK(BH+) = 28.1 and 27.1 in CD(3)CN), resulting in a catalytic activity for the Michael addition of nitromethane with α,β-unsaturated carbonyl compounds.     

A simple catalytic method for the regioselective halogenation of arenes

This paper describes a mild palladium-catalyzed method for the regioselective chlorination, bromination, and iodination of arene C-H bonds using N-halosuccinimides as oxidants. These transformations have been applied to a wide array of substrates and can provide products that are complementary to those obtained via conventional electrophilic aromatic substitution reactions. [reaction: see text]     

Highly regioselective, catalytic asymmetric reductive coupling of 1,3-enynes and ketones

[reaction: see text] Highly regioselective, catalytic asymmetric reductive coupling reactions of 1,3-enynes and ketones have been achieved using catalytic amounts of Ni(cod)(2) and a P-chiral, monodentate ferrocenyl phosphine ligand. These couplings represent the first examples of catalytic, intermolecular reductive coupling of alkynes and ketones, enantioselective or otherwise, and afford synthetically useful 1,3-dienes possessing a quaternary carbinol stereogenic center in up to 70% ee.     

Functionalization of a simple dithienylethene via palladium-catalyzed regioselective direct arylation

The direct arylation on the thienyl groups of a diarylethene with various aryl iodides efficiently provided arylated dithienylethenes under palladium catalysis. Unsymmetrically substituted dithienylethenes were also synthesized by this protocol. This procedure allows a rapid access to a variety of aryl-substituted dithienylethenes from a single substrate of a simple dithienylethene.     

Influence of intramolecular hydrogen bonds in the enzyme-catalyzed regioselective acylation of quinic and shikimic acid derivatives

Selective mono-functionalization of 3-epi, 4-epi-, and 5-epi quinic and shikimic acid derivatives has been accomplished by enzymatic acylation with Candida antarctica lipase A (CAL-A). We propose that the selectivity of this lipase is related to both the inherent receptor selectivity and the degree of intramolecular hydrogen bonding in the ligand. Conformational analysis of the hydroxyl protons has been carried out by ¹H NMR spectroscopy. We have shown that exchange of the hydroxyl protons by acid catalysis provides a useful method for the detection of intramolecular hydrogen bonds. The interpretation of exchange rates and coupling constants determines the direction of the H-bonds as conditioned by the relative acceptor and donor properties of the hydroxyl groups. The selectivity of the acylation agrees fully with the effectiveness of H-bonding networks in polyol compounds and with the higher reactivity of the equatorial hydroxyl groups.     

Ammonia reactivity in the acylation with 4-nitrophenyl benzoate in a water-2-propanol system

The kinetics of acylation of ammonia with 4-nitrophenylbenzoates in water-2-propanol mixtures was studied. Increase in the reaction rate with increasing proportion of water in the system is attributed to the formation of ammonia solvato complexes with the components of the solvent. By the RHF/6-31G* method were calculated structural and energetic properties of the solvato complexes. The potential energy surfaces of the acylation reaction of ammonia and its solvato complexes were calculated. It was shown that solvation of the transition state decreases the reaction activation energy compared to the gas-phase process. All the reactions proceed by S _N2 mechanism without formation of intermediates, with only one transition state.     

Indole-2,3-quinodimethanes: Generation, reactivity and regioselective control of intermolecular Diels-Alder reactions

N-acylindole-2,3-quinodimethanes generated at low temperature from the N-acyl-2,3-bis (bromomethyl)indoles undergo a variety of cycloadditions including the reversible chelotropic reaction with sulphur dioxide to yield the unreported 1,3-dihydrothieno[3,4-b]indole-2,2-dioxide 9. Successful attempts to control the regioselectivity of reactions with unsymmetrical dienophiles are described.     

In situ demonstration and quantitative analysis of the intrinsic properties of glycoside hydrolases

Based on digital image analysis techniques and a series of optimizations in native electrophoresis, a new direct method to simultaneously detect the intrinsic properties of each active component in the enzymatic system of glycoside hydrolase was established. The key technique is that the concentration changes of substrate (or product) on the gel can be determined quantitatively by the gray value changes of the corresponding band after electrophoretic separation. In this manner, the catalytic characteristics of each glycoside hydrolase component were demonstrated in situ and were easily determined after immersing the gel in a series of solutions containing substrates or their derivatives. Because of its high throughput, great sensitivity, and convenient operation, this method can be used to demonstrate the natural diversity of glycoside hydrolases and to study spatial and temporal regulation in multienzyme expression systems. Thus, it is an effective approach to study the functional proteomics of glycoside hydrolases.     

Fine tuning the reactivity of corrole-based catalytic antioxidants

In order to determine the electronic factors that may affect the catalytic antioxidant activity of water-soluble metallocorroles a series of 10-aryl-5,15-pyridinium manganese(III) corroles was prepared. These complexes were examined regarding the effect of the C(10) substituent on the Mn(IV)/Mn(III) redox potentials, catalytic rate constants for decomposition of HOONO, prevention of tyrosine nitration, and superoxide dismutase activity. This structure-activity relationship investigation provides new insight regarding the mechanism by which manganese(III) corroles act as catalytic antioxidants. It also discloses the superiority of the C(10)-anysil-substituted complex in all examined aspects.     

Preparation of an analogue of orbicuside A,an unusual cardiac glycoside

A steroid containing a multi-linked glycoside, analogous to the bufadienolide orbicuside A, has been prepared. The key steps were (i) the preparation of a 2α-allyloxycarbonyloxy-3β-hydroxy steroid, (ii) a Ferrier reaction between the steroid and a rhamnal derivative, (iii) removal of protecting group and oxidation of the 2-hydroxy group, (iv) dihydroxylation of the pseudoglycal from the sterically more hindered side and finally (v) ring closure by acetal formation under acidic conditions.     

Construction of CdS quantum dots via a regioselective dendritic functionalized cellulose template

Using regioselective dendritic functionalized cellulose, CdS quantum dot nanoparticles were prepared and their photo-optical properties and morphology as well as the preliminary biocompatibility of the hybrid were investigated.     

Highly regioselective synthesis of 1,3-diiodonaphthalene derivatives via a sequential cascade iodocyclization

A novel and flexible sequentially cascade iodocyclization for the synthesis of highly substituted 1,3-diiodinated naphthalene derivatives in up to 99% yield under mild conditions is reported. The dihalogenated moiety can be readily introduced into the naphthalenes in a position that is usually not easily functionalized.