Influence of β-substituents in aldol reactions of boron enolates of β-alkoxy methylketones

Moderate to good levels of substrate-based 1,5-syn-stereocontrol could be achieved in the boron-mediated aldol reactions of β-tert-butyl methylketones with achiral aldehydes, independent of the nature of the β-alkoxy protecting group (P = PMB or TBS). The analysis of the relative energies of the transition structures by theoretical calculations using the density functional B3LYP shows relative energies favoring the corresponding OUT-1,5-SYN transition structures, explaining the observed 1,5-syn stereoinduction.     

Structure determination of glycopeptide of β-momorcharin

The structure of the N-linked oligosaccharide chain of β-momorcharin, a ribosome-inactivating protein from the seeds of Momordica charantia Linn (Cucurbitaceae), was determined. A glycopeptide liberated by pronase digestion of the glycoprotein was subjected to amino acid and neutral carbohydrate analysis to establish the composition of amino acid and sugar residues. The sequences and glycosylation hnkages of the sugar and amino acid residues in the glycopeptide were determined as Manαl-6(XyIβ1-2)-Manβ1-4GlcNAcβ1-4(Fucαl-3)-GlcNAc-Asn-Leu by 2D-NMR spectroscopy and FAB-MS data.     

Preparation of β-fluoro- and β,β-difluoro-histidinols

Nucleophilic attack of azide on 2-bromo-3-fluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1a) in aprotic solvent occurs on the 2-position to give the 2-azido derivative (2a). Reduction of azide and removal of the trityl group produces β-fluorohistidinol (6a). Elimination of HBr from 1a followed by “FBr” addition to the resulting double bond gives 2-bromo-3,3-difluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1b). Nucleophilic attack of azide followed by reduction and removal of the trityl group, as for the preparation of 6a, gives β,β-difluorohistidinol (6b). Initial attempts, under a variety of conditions, to oxidize the fluorinated histidinol precursors to carboxylic acids have not been successful.     

Synthesis of fluoroalkyl-containing β-hydroxyketones by reduction of the corresponding β-diketone derivatives

The rcgioselective synthesis of fluoroalkyl-containing P-hydroxyketones by the reduction of the salts of the corresponding -diketones with LiAlH₄ was proposed. This is the sole method for the synthesis of -hydroxyketones with two fluoroalkyl substituents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1493–1495, June, 1996.     

Synthesis of Unsymmetrical β-Arylaminoketones

Azomethines derived from aniline were condensed with acetophenone derivatives to obtain new unsymmetrical -arylaminoketones.     

Regioselective Acetylation of β-Cyclodextrin

One-stage methods of synthesis of water-soluble -cyclodextrins selectively acetylated by primary or secondary hydroxy groups have been found, that make use of acetyl chloride and hydrogen chloride acceptors of different nature.     

New Synthesis of β-Iodostyrenes

A general procedure for the synthesis of -iodostyrenes is proposed. Aromatic aldehyde and ketone hydrazones are converted into the corresponding -iodostyrenes by treatment with CHI₃ in the presence of a catalytic amount of CuCl.     

Selective synthesis of β-alkylpyrroles

β-Alkylpyrroles are key structural motifs found in many natural products and biologically active compounds as well as functional organic materials. For this reason, synthetic chemists continue to be interested in construction of the framework of β-alkylpyrroles. Due to sufficient aromaticity and π-excessive nature of pyrroles, a straightforward approach to β-alkylpyrroles should be electrophilic aromatic substitution (S(E)Ar) toward the pyrrole ring. However, since a primary nucleophilic site of pyrroles is an α-position, some "trick" is required to direct incoming alkyl electrophiles toward a β-position. This Concept article focuses on presenting previous efforts that have been devoted to the synthesis of β-alkylpyrroles, mainly through the S(E)Ar route.     

Adamantylation of β-dicarbonyl compounds

Reactions of adamantan-1-ol with β-dicarbonyl compounds in 1,2-dichloroethane in the presence of In(OTf)₃, Ga(OTf)₃, Sc(OTf)₃, or Cu(OTf)₂ give the corresponding adamantylated derivatives in 45–93% yields.     

The Preparation of β-Hydroxysulfoxides

. Oxidation of β-hydroxy thioethers with MnO₂-aqu. 35%/HCl in methanol gives β-hydroxy sulfoxides in high yields.     

Enantioselective synthesis of β-amino-diacids

An efficient route to orthogonally protected β-amino-diacids is described: chiral derivative 3 was shown to be a precursor of enantiopure substituted β-amino acids. The key step of the procedure is a diastereoselective reduction of β-enaminolactones 5 by NaBH₃CN in CH₂Cl₂. A study concerning the regio- and diastereoselectivity of alkylation of β-enaminolactone 3 is also presented.     

Synthesis of β-Stannyl Esters

A synthesis of β-stannyl esters from ester enolates and iodomethyl (tri-n-butyl) stannane (3) is described.     

Selective monoallylation of β-cyclodextrin

Reaction of β-cyclodextrin with allyl bromide in dimethyl sulfoxide affords 2-О-allyl-β-cyclodextrin, while in dimethylformamide 6-О-allyl-β-cyclodextrin is formed. Optimal conditions of the reaction were found allowing to obtain the target products in quantitative yield.     

Fragmentation of β-hydroxy hydroperoxides

A β-hydroxy hydroperoxide was obtained through base-catalyzed disproportionation of a hydroperoxy endoperoxide available by singlet oxygenation of cyclohepta-1,4-diene. Vitamins E and C induce fragmentation of this β-hydroxy hydroperoxide generating aldehydes, especially in the presence of redox active metal ions such as those present in vivo, e.g., under conditions of "iron overload". This chemistry may contribute to the oxidative cleavage of polyunsaturated fatty acyls that produces similar aldehydes, which damage proteins and DNA through covalent adduction resulting in "oxidative injury".     

One-pot synthesis of β-imidazolylpropionamides

New efficient one-pot methodology for the preparative synthesis of β-imidazolylpropionamides was elaborated. It is based on the addition of imidazole to the activated double bond of the intermediate acrylimidazolide in the reaction between diverse acrylic acids and different amines promoted by CDI. A set of structurally and functionally diverse β-imidazolylpropionamides was obtained in high preparative yields.     

Practical synthesis of β-acyl and β-alkoxycarbonyl heterocyclic sulfones

A short and efficient synthesis for β-acyl and β-alkoxycarbonyl heterocyclic sulfones containing benzothiazol (BT) and phenyltetrazol (PT) heterocyclic core is presented here. The method seems to be general and provides the desired C-nucleophiles in very good to excellent yields from readily available starting materials.     

Synthesis and biological investigation of the β-thiolactone and β-lactam analogs of tetrahydrolipstatin

The synthesis of β-thiolactone and β-lactam analogs of tetrahydrolipstatin is described from a common late-stage β-lactone derivative. These analogs, and a cis-disubstituted β-lactone analog of tetrahydrolipstatin, were screened for activity against porcine pancreatic lipase and for inhibition of cell growth of a panel of four human cancer lines.     

Prediction of the activity of β-lactam antibiotics

The pharmacological properties of penam, 3-cepheme, and semisynthetic penicillins were predicted by means of the ORAKUL automated system. A comparative evaluation of the similarity between the structures of these compounds and the structures of 8800 biologically active substances in the data base of the system made it possible to uncover the high probability of the manifestation of anti-inflammatory, analgesic, antitumorigenic, antiallergic, and anticoagulant activity by structural analogs of -lactam antibiotics.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 555–564, April, 1992.