A simple and selective kinetic spectrophotometric method for the determination of kanamycin using acetylacetone-formaldehyde reagent in N,N′-dimethylformamide medium

A simple, sensitive, and selective kinetic spectrophotometric method for the determination of kanamycin in pure form and pharmaceutical formulations is described. The method is based on the measurement of the intensity of the yellow chromogen formed by the reaction between kanamycin and acetylacetone-formaldehyde reagent in a N,N′-dimethyl formamide medium. The variable-time method was used to evaluate the rate of reaction of the colored chromogen formed at 410 nm. The reaction conditions were optimized and the calibration graph was found to be linear in the range 60–160 μg/mL. The results obtained by the developed and reference methods are in good agreement. Various statistical parameters were evaluated to establish the precision, accuracy, repeatability, and reproducibility of the proposed method. The text was submitted by the authors in English.     

Synthesis and crystal structure of a covalently hydrated 8-thia-1,4-diazacycl[3.3.2]azine

Condensation of ethyl 4-chloroacetoacetate with 4-amino-6-hydroxy-2-pyrimidinethiol produced ethyl 3-hydroxy-5-amino-7-oxothiazolino[3,2-a]pyrimidin-3-acetate ( 7a ) on crystallization. Subsequent ring closure of 7a produced the tricyclic 6a-hydroxy-5,6,6a,7-tetrahydro-8-thia-1,4-diazacycl[3.3.2]azin-2,5-dione ( 8 ). The structure of 8 was confirmed by crystal x-ray diffraction analysis.     

The μ3-cyclopentadienylidene ligand: X-ray structure of [Ru4(CO)5 {P(OMe)3}(μ3-C5H4)2(η-C5H5)2]

UV irradiation of [Ru₂(CO)₄(η-C₅H₅)₂] yields the tri- and tetra-ruthenium complexes [Ru₂(CO)₄(η-C₅H₅){η-C₅H₄Ru(CO)₂(η-C₅H₅)}] and [Ru₄(CO)₆(μ₃-C₅H₄)₂(η-C₅H₅)₂]. The μ₃-C₅H₄ ligand in the latter has been characterised through an X-ray diffraction study on [Ru₄(CO)₅{P(OMe)₃}(μ₃-C₅H₄)₂(η-C₅H₅)₂].     

Novel concentration-driven structural interconversion in shape-specific solids supported by the octahedral [Re(6)(mu3-Se)8]2+ cluster core

A complex containing the face-capped octahedral [Re(6)(mu(3)-Se)(8)](2+) cluster core, cis-[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)](SbF(6))(2) (1), is used as a ditopic ligand with an enforced right angle between the two 4,4'-dipyridyl moieties for the coordination of Cd(2+) ion. Two coordination polymers, [[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)](2)[Cd(NO(3))(2)]](SbF(6))(4).21C(4)H(10)O.21CH(2)Cl(2) (2) and [[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)][Cd(NO(3))(3)]](NO(3)).2C(4)H(10)O.CH(2)Cl(2) (3), are obtained. The relative concentration of Cd(2+) determines which species is isolated, and the conversion of the first structure into the second is demonstrated experimentally.     

C-C bond formation at polynuclear metal centers

Studies on C-C bond formation between simple hydrocarbon species such as CH₂, C=CH₂, CH=CH₂, CH₂=CH₂, CH₂=C=CH₂ and CHCH at a diruthenium center suggest that the process is promoted when the dimetal center can readily compensate for the two electrons lost in the formation of the new C-C bond. Thus, whereas -CH₂ and ethene combine only under forcing conditions, the combination of -CH₂ with allene or ethyne, which have additional -electrons available for coordination, occurs readily at room temperature. Likewise, the availability of uncoordinated -electrons in -C=CH₂ allows vinylidene to link rapidly with ethene at room temperature. Alkyne complexes [Ru₂(CO)(-RCCR)(-C₅H₅)₂] (R=CF₃ or Ph) react only under vigorous conditions with additional alkyne to give [Ru₂(CO)(-C₄R₄) (-C₅H₅)₂], but give these same species at room temperature in the presence of acid, shown to be due to the intermediacy of highly reactive 30-electron -vinyl cations. Thermally, alkyne linking proceedsvia three-alkyne species [Ru₂(-C₆R₆)(-C₅H₅)₂] to a four-alkyne complex [Ru₂(-C₈R₈)(-C₅H₅)₂], containing an unprecedented C₈ ligand composed of a C₆ ring with a C₂ tail. Treatment of [Ru₂(CO)(-RCCR)(-C₅H₅)₂] with unsaturated metal fragments gives trimetal complexes such as [Ru₃(CO)₅(₃-CF₃CCCF₃) (-C₅H₅)₂]. The MeCN derivative of this species undergoes unusual linking processes on reaction with additional alkyne to giveinter alia [Ru₃(CO)₃(₃-CCF₃){₃-C₃(CF₃)₃}(-C₅H₅)₂], arising from alkyne cleavage, and [Ru₃(CO)₃{₃-C₄(CF₃)₂(CO₂Me)₂}(-C₅H₅)₂], a closo-pentagonal bipyramidal Ru₃C₄ cluster.     

Synthesis of novel dihydrothiazolo[3,2-a]pyrimidinone derivatives

Condensation of 2-amino-4-hydroxy-2-mercaptopyrimidine (2) hydrate and ethyl 4-bromocrotonate gave a mixture of ethyl 7-amino-2,3-dihydro-5-oxo-5H-thiazolo[3,2-a]pyrimidine-3-acetate (4) and 2a,3-dihydro-1-thia-5,8,8b-triazaacenaphthylene-4,7(2H)-dione (5) whereas reaction of 2 with 4-bromocrotononitrile afforded only 7-amino-2,3-dihydro-5-oxo-5H-thiazolo[3,2-a] pyrimidine-3-acetonitrile. Reaction of the tricycle 5 (which was isolated as a hemihydrate) with excess methyl iodide/potassium carbonate in dimethylformamide resulted in both ring hydrolysis and methylation to give 3,4-dihydro-1,7-dimethyl-4- [(methylthio)methyl]-2H-pyrimido[1,6-a]pyrimidine-2,6,8(1H,7H)-trione (10). Methylating 5 with excess methyl iodide/sodium methoxide in methanol also resulted in ring fragmentation and methylation but instead afforded methyl 7-methyl-amino-2,3-dihydro-5-oxo-7H-thiazolo[3,2-a]pyrimidine-3-acetate. The mechanistic aspects of these reactions are discussed.     

Direct observation of the gas-phase Criegee intermediate (CH2OO)

Carbonyl oxide species play a key role in tropospheric oxidation of organic molecules and in low-temperature combustion processes. In the late 1940s, Criegee first postulated the participation of carbonyl oxides, now often called "Criegee intermediates," in ozonolysis of alkenes. However, despite decades of effort, no gas phase Criegee intermediate has before been observed. As a result, knowledge of gas phase carbonyl oxide reactions has heretofore been inferred by indirect means, with derived rate coefficients spanning orders of magnitude. We have directly detected the primary Criegee intermediate, formaldehyde oxide (CH2OO), in the chlorine-initiated gas-phase oxidation of dimethyl sulfoxide (DMSO). This work not only establishes that the Criegee intermediate is formed in DMSO oxidation also but opens the possibility for explicit kinetics studies on this critical atmospheric species.     

A group structure on squares

We show that there is an abelian group structure on the orbit set of ``squares' of unimodular rows of length over a commutative ring of stable dimension when , odd and also an abelian group structure on the orbit set of ``fourth powers' of unimodular rows of length over a commutative ring of stable dimension when , even.

     

Synthesis, structures and reactivity of group 4 hydrazido complexes supported by calix[4]arene ligands

Reaction of TiCl(2)(Me(2)Calix) with 2 equiv of LiNHNRR' afforded the corresponding terminal hydrazido(2-) complexes Ti(NNRR')(Me(2)Calix) (R = Ph, R' = Ph (1) or Me; R = R' = Me (3)) which were all structurally characterized. The X-ray structure of Ph(2)NNH(2) is reported for comparison. Compound 1 was also prepared from Na(2)[Me(2)Calix] and Ti(NNPh(2))Cl(2)(py)(3). Reaction of ZrCl(2)(Me(2)Calix) with 2 equiv of LiNHNR(2) afforded only the bis(hydrazido(1-)) complexes Zr(NHNR(2))(2)(Me(2)Calix) (R = Ph or Me). Treatment of Ti(NNMe(2))(Me(2)Calix) (3) with MeI gave the zwitterionic hydrazidium species Ti(NNMe(3))(MeCalix) (6) via a net isomerization reaction which was found to be catalytic in MeI. The corresponding reaction of 3 with CD(3)I gave Ti(NNMe(2)CD(3))(MeCalix) (6-d(3)) with concomitant elimination of MeI. Reaction of 3 with 1 equiv of MeOTf gave [Ti(NNMe(3))(Me(2)Calix)][OTf] (7-OTf) which in turn reacted with (n)Bu(4)NI to form 6 and MeI. Addition of PhCHO to 3 gave the mu-oxo dimer [Ti(mu-O)(Me(2)Calix)](2) and benzaldehyde-dimethylhydrazone. Reaction of either 3 or 6 with (t)BuNCO gave the zwitterionic species Ti{(t)BuNC(NNMe(3))O}(MeCalix) (10) which has been crystallographically characterized. Compound 10 is the formal product of insertion of an isocyanate into the Ti=N(alpha) bond of a titanium hydrazide or hydrazidium species (Me(2)Calix or MeCalix = dianion or trianion of the di- or monomethyl ether of p-tert-butyl calix[4]arene, respectively).     

Initial synthesis of UK-427,857 (Maraviroc)

The initial synthesis of UK-427,857 (Maraviroc) is described including the preparation of 4,4-difluorocyclohexanoic acid and amide coupling utilizing a polymer supported reagent.