Novel bi- and tridentate phosphane and thioether ligands derived from chiral α-hydroxy acids

Novel bi- and tridentate ligands with phosphane and thioether moieties have been prepared in enantiomerically pure form in good to excellent yields by substitution reactions with phosphorus and sulfur nucleophiles of easily available tosylates derived from natural chiral α-hydroxy acids.     

Cyclic hydroxamic acids derived from α-amino acids 1. Regioselective synthesis,structure, NO-donor and antimetastatic activities of spirobicyclic hydroxamic acids derived from glycine and DL-alanine

The reactions of glycine hydroxamic and DL-alanine hydroxamic acids with triacetonamine are chemoselective and afford 1-hydroxy-7,7,9,9-tetramethyl-1,4,8-triazaspiro[4.5]decan-2-one (3) and (±)-1-hydroxy-3,7,7,9,9-pentamethyl-1,4,8-triazaspiro[4.5]decan-2-one (4), respectively. The X-ray diffraction study showed that compound 3 crystallizes as a solvate with MeCN (1: 1). As shown by ESR measurements, spiro hydroxamic acids 3 and 4 are NO donors in in vitro biological systems. The NO-donor activity of compounds 3 and 4 was found to be substantially higher in the presence of DMSO. Homologue 4 is a stronger NO donor than 3. Compound 4 also exhibits high antimetastatic activity (81%) on the B16-melanoma model.     

Synthesis and resolution of new paramagnetic α-amino acids

New, paramagnetic unnatural α-amino acids were synthesized by the O'Donnell method. In the new amino acids nitroxide is condensed with thiophene, benzene, and tetrahydroisoquinoline ring, or linked through a methylene, benzyl or propargyl spacer. Some of the racemic paramagnetic α-amino acid esters described earlier or in this work were resolved by fractional crystallization of diastereomeric salts. Another approach for optically active paramagnetic amino acids is the modification of S-tyrosine derivatives with Pd-catalyzed cross-coupling reactions with paramagnetic acetylene and with a paramagnetic boronic acid.     

Synthesis of diazoketones derived from α-amino acids; problem of side reactions

Optimum conditions of synthesis of eight diazoketones derived from optically active N-(t-butyloxycarbonyl)- and N-benzyloxycarbonylamino acids have been described. The problem of formation of by-products during Arndt-Eistert synthesis of β-homoamino acids at the stage of reaction of mixed anhydride with a weak nucleophile-diazomethane - has been discussed.     

Facile synthesis of α-hydroxy carboxylic acids from the corresponding α-amino acids

An effective and improved procedure is developed for the synthesis of α-hydroxy carboxylic acids by treatment of the corresponding protonated α-amino acid with tert-butyl nitrite in 1,4-dioxane–water. The amino moiety must be protonated and located α to a carboxylic acid function in order to undergo initial diazotization and successive hydroxylation, since neither β-amino acids nor acid derivatives such as esters and amides undergo hydroxylations. The method is successfully applied for the synthesis of 18 proteinogenic amino acids.     

Synthesis and structure of cobalt α-dioximate complexes with isonicotinamide

New cobalt trans-dioximate complexes with isoniconinamide have been synthesized: [Co^II(DmgH)₂(Inia)₂] (I), [Co^III(DmgH)₂(Inia)₂][PF₆] · 1.5H₂O (II), [Co^III(NioxH)₂ (Inia)₂][PF₆] · H₂O · CH₃OH (III), and [CoIIICl(DmgH)₂(Inia)] · H₂O (IV), where DmgH⁻ and NioxH⁻ are the dimeth-ylglyoxime and 1,2-cyclohexanedionedioxime monoanions, respectively; Inia is the isonicotinamide molecule. The structures of compounds I–IV have been determined by X-ray crystallography. In I–IV, Co(II) or Co(III) has an octahedral environment with the pseudomacrocyclic (DioxH⁻)₂ moiety (DioxH⁻ is the dioximate monoanion) in the equatorial plane. The latter is stabilized by O-H…O hydrogen bonds. The isonicotinamide molecules in all four complexes are monodentately bound to the metal ion through the heterocyclic nitrogen atom.     

Synthesis of chalcones derived from (+)- and (?)-usnic acids

A number of chalcones with the (+)- and (?)-usnic acid moieties were synthesized by the following sequence: the reaction of these acids with phenylhydrazine, reduction of the C(1)=O group with sodium borohydride, O-methylation of the intermediate compounds with diazomethane, and subsequent condensation with substituted benzaldehydes at the acetyl group.     

Absolute configurational assignment of α-hydroxy acids and α-hydroxy esters from their Cupra A circular dichroism spectra

The in situ formed complexes of cuprammonium solution (Cupra A) with optically active α-hydroxy acids and α-hydroxy esters show circular dichroism spectra suitable for determination of the absolute configuration of both groups of compounds. In the long wavelength spectral region, compounds of R configuration at the α carbon atom display a positive Cotton effect of around 600 nm and a negative one at ca. 720 nm, whereas (S)-α-hydroxy acids and esters exhibit negative and positive Cotton effects, respectively, in the same spectral range.     

Synthesis of trifluoromethylated α-hydroxy acids and their derivatives based on alkyl trifluoropyruvates

The reactions of trifluoropyruvates with nitromethane and arylmagnesium bromides leading to trifluoromethyl-containing α-hydroxy acid esters were studied and various derivatives of the acids were obtained.     

Synthesis of β-amino ketones derived from aminobenzoic acids

Russian Journal of General Chemistry - Alkylation of aminobenzoic acids and their derivatives with 3-diethylamino-1-arylpropan-1-one hydrochlorides gave the corresponding β-aminopropiophenones...     

Synthesis of furanyl- and triazolyl-containing α-CF3-α-hydroxy acids and their derivatives

Russian Chemical Bulletin - Starting from methyl trifluoropyruvate, α-CF3-substituted α-methoxy-α-(furan-2-yl) acetic acids and their derivatives and also methyl...     

Synthesis and asymmetric oxidation of thioglycosides derived from neomenthanethiol and α-d-galactose

6-Deoxy-6-[(1S,2S,5R)-2-isopropyl-5-methylcyclohexylsulfanyl]-1,2:3,4-di-O-isopropylidene-α-d-galactopyranose was synthesized in 94% yield from 1,2 : 3,4-di-O-isopropylidene-α-d-galactopyranose and neomenthanethiol, and its oxidation gave the corresponding diastereoisomeric sulfoxides in up to 84% yield and de values of up to 52%. The isopropylidene protective groups were removed from the sulfide and sulfoxides by treatment with trifluoroacetic acid in chloroform.     

Synthesis and anion-exchange reactions of a new anionic clay, α-magnesium hydroxide

A new anionic clay, α-magnesium hydroxide, was synthesized by hydrolysis of magnesium acetate in propylene glycol. The structure of this α-hydroxide is similar to that of hydrotalcites. It consists of positively charged magnesium hydroxide layers arising out of partial protonation of the hydroxyl groups of the [Mg(OH)(2)] layers and loosely held anions in the interlayer region. As expected it ages readily in water to give β-magnesium hydroxide, brucite. While anion-exchange reactions of α-magnesium hydroxide could not be carried out in aqueous medium a number of anion-exchange reactions could be carried out successfully in ethanol medium.     

Synthesis of new α-hydroxyphosphonates and α-acetoxyphosphonates

A series of new α-hydroxyphosphonate (5–14) have been synthesized in high yields by reaction of β-chloro-α,β-unsaturated aldehydes (1–4) and trialkyl phosphite in the presence of chlorotrimethylsilane at room temperature under solvent-free conditions. In addition, compounds (5–14) were reacted with acetic anhydride in DBU to give the new α-acetoxyphosphonate derivatives (15–23). All these phosphonates (5–23) were obtained as mixtures of two (E and Z) isomers and fully characterized by multinuclear (¹H, ¹³C, and ³¹P) NMR, IR spectroscopy and HRMS.     

Synthesis of polyhydroxylated α-nitrocyclohexane carboxylic acids derived from d-glucose: a striking case of racemization

The first total synthesis of polyhydroxylated α-nitrocyclohexane carboxylic acids from sugars is reported. A salient aspect of the synthesis is an unexpected Henry-mediated racemization of this new class of highly functionalized cyclohexanes.     

Synthesis,characterization, molecular and supramolecular structures of nickel(II) complexes derived from α-diketone and α-ketoaldehyde bisaroylhydrazones

A new series of nickel(II) complexes derived from symmetrical diacetyl bisaroylhydrazones [Ni(L¹-R)] and unsymmetric phenylglyoxal bisaroylhydrazones [Ni(L²-R)] have been prepared and characterized. X-ray crystal and molecular structures of [Ni(L¹-H)], [Ni(L¹-pCH₃O)] and [Ni(L¹-pNO₂)] have been determined. In these complexes, the Ni(II) is in a distorted square planar environment and the aroylhydrazone acts as dinegative tetradentate ligand forming a 5,5,5-tricyclic chelate ring. Reaction of [Ni(L¹-R)] with aqueous ammonia afforded the paramagnetic five coordinate [Ni(L¹-R)(NH₃)] while [Ni(L²-R)] gave the diamagnetic square planar [Ni(L²-R)(NH₃)] complexes. Reaction of [Ni(L¹-R)] complexes with imidazole gave the corresponding paramagnetic octahedral bis(imidazole) adducts. X-ray structures of both [Ni(L¹-H)(HIm)₂] and [Ni(L¹-pNO₂)(HIm)₂] suggest a distorted octahedral structure where the bisaroylhydrazone occupies the basal plane while the two imidazoles occupy the axial sites. The molecular units are associated together forming triple stranded helical chains. With imidazole the [Ni(L²-R)] series gave the corresponding diamagnetic mono(imidazole) [Ni(L²-R)(HIm)] complexes, The X-ray structure of {Ni(L²-pCH₃)(HIm)] suggest square planar arrangement around the Ni(II) where the bisaroylhydrazone acts as dinegative NNO tridentate ligand forming with the Ni(II) a 5,6-bicyclic chelate ring the fourth coordination site is occupied by imidazole nitrogen.     

Synthesis,characterization and biological activity of copper(II) complexes with ligands derived from β-amino acids

Transition Metal Chemistry - Two copper(II) complexes with ligands derived from β-amino acids, 2-(1-aminocyclohexyl)acetic acid L1 and 2-(1-amino-4-(tert-butyl)cyclohexyl)acetic acid L2, were...     

Synthesis and antiviral properties of tricyclic amides derived from α-humulene and β-caryophyllene

The Ritter reaction of humulene with acetonitrile occurs as the biomimetic process to afford the amide having the skeleton of a natural alcohol. The structures of the amides obtained from humulene and caryophyllene were confirmed by XRD data. The activity of some cage compounds against influenza virus allowed one to suggest the mechanism of antiviral action based on interfering with membrane fusion activity of viral hemagglutinin.     

Synthesis and application of enantioenriched functionalized α-tetrasubstituted α-amino acids from biocatalytic desymmetrization of prochiral α-aminomalonamides

Catalyzed by Rhodococcus erythropolis AJ270, an amidase-containing microbial whole cell catalyst in neutral phosphate buffer at 30 °C, a number of prochiral α-substituted α-aminomalonamides underwent highly efficient and enantioselective hydrolytic desymmetrization to afford functionalized α-tetrasubstituted α-amino acids in 74-98% chemical yields and 94.0 to >99.5% ee. The presence of a free α-amino (NH(2)) substituent in the substrates was deemed important to ensure high biocatalytic efficiency and enantioselectivity. The synthetic application of biocatalytic desymmetrization was demonstrated by practical chemical transformations of (R)-2-amino-2-carbamoylpent-4-enoic acid to α-substituted serine analogues and a bioactive diamino alcohol derivative.