Acyclic Organic Compounds Research Articles

NHC-Catalyzed Enantioselective Transformations Involving α-Bromoenals.

α-Haloenals, especially, α-bromoenals considered as one of the important building blocks in organic synthesis. They can participate in various (3+2)-, (3+3)-, (3+4)-, and (2+4)-annulation reactions with other organic molecules in the presence of an NHC catalyst to produce enantioenriched carbo-, and heterocyclic compounds. Herein, we have described NHC-catalyzed enantioselective transformations of α-bromoenals in the synthesis of various heterocycles, and carbocycles, as well as acyclic organic compounds.

Supramolecular Paradigm for Capture and Co‐Precipitation of Gold(III) Coordination Complexes

A new supramolecular paradigm is presented for reliable capture and co-precipitation of haloauric acids (HAuX4 ) from organic solvents or water. Two classes of acyclic organic compounds act as complementary receptors (tectons) by forming two sets of directional non-covalent interactions, (a) hydrogen bonding between amide (or amidinium) NH residues and the electronegative X ligands on the AuX4 - , and (b) electrostatic stacking of the electron deficient Au center against the face of an aromatic surface. X-ray diffraction analysis of four co-crystal structures reveals the additional common feature of proton bridged carbonyls as a new and predictable supramolecular design element that creates one-dimensional polymers linked by very short hydrogen bonds (CO⋅⋅⋅OC distance <2.5 Å). Two other co-crystal structures show that the amidinium-π⋅⋅⋅XAu interaction will reliably engage AuX4 - with high directionality. These acyclic compounds are very attractive as co-precipitation agents within new "green" gold recovery processes. They also have high potential as tectons for controlled self-assembly or co-crystal engineering of haloaurate composites. More generally, the supramolecular paradigm will facilitate the design of next-generation receptors or tectons with high affinity for precious metal square planar coordination complexes for use in advanced materials, nanotechnology, or medicine.

ChemInform Abstract: Isocyanide and Meldrum′s Acid‐Based Multicomponent Reactions in Diversity‐Oriented Synthesis: From a Serendipitous Discovery Towards Valuable Synthetic Approaches

AbstractReview: 102 refs.

Interdisciplinary Aspects of Organic Chemistry-cum-Graph Theory

The distinction between interdisciplinarity, multidisciplinarity, and transdisciplinarity is emphasized. Chemistry evolved later as a science than physics, so that in the early 19th century renowned philosophers denied the possibility of mathematics being useful for chemical problems. Later, with the advent of quantum mechanics, chemistry was viewed as reducible to physics. It is argued, however, that mathematical chemistry – discrete mathematics and graph theory – can explain chemical phenomena and concepts without the intermediacy of physics. Isomer enumeration of cyclic and acyclic organic compounds (as molecular graphs) contributed to the birth of graph theory. Aromatic heterocyclic compounds can be described and enumerated according to three types of atoms forming the aromatic ring, according to the number (0, 1, or 2) of π-electrons in the non-hybridized orbital. Benzenoids and diamondoids can be classified, described and enumerated with the help of dualists. In polycyclic benzenoids, various π-electron partitions are possible, and among them the Clar-sextet partition is the most unequal. Topological indices that associate numbers with molecular structures are instruments for quantitative structure-property or structure-activity relationships (QSPR and QSAR, respectively) and drug design. Reaction graphs and synthon graphs are also mentioned. Reciprocal interaction – from chemistry to mathematics – accounts for the discovery of new (3,g)-cages and upper/lower bounds of various energy graphs or graph connectivities.

環状ニッケル化合物を反応中間体とする分子変換反応

Nickelacycles have been known as a key reaction intermediate. The β-hydrogen transfer reactions from nickelacycles allow us to synthesize acyclic organic compounds. The reductive elimination from nickelacycles allows us to synthesize a variety of cyclic organic compounds. Thus, the generation of a new nickelacycles from a new combination of unsaturated compounds and nickel(0) species is a key to develop nickel-catalyzed new reactions. We report here the new molecular transformations of a variety of unsaturated compounds via nickelacycles in which both acyclic and cyclic compounds were obtained. In addition, the isolation of the reaction intermediates and their reaction mechanisms are discussed as well.

Predicting Physical−Chemical Properties of Compounds from Molecular Structures by Recursive Neural Networks

In this paper, we report on the potential of a recently developed neural network for structures applied to the prediction of physical chemical properties of compounds. The proposed recursive neural network (RecNN) model is able to directly take as input a structured representation of the molecule and to model a direct and adaptive relationship between the molecular structure and target property. Therefore, it combines in a learning system the flexibility and general advantages of a neural network model with the representational power of a structured domain. As a result, a completely new approach to quantitative structure-activity relationship/quantitative structure-property relationship (QSPR/QSAR) analysis is obtained. An original representation of the molecular structures has been developed accounting for both the occurrence of specific atoms/groups and the topological relationships among them. Gibbs free energy of solvation in water, Delta(solv)G degrees , has been chosen as a benchmark for the model. The different approaches proposed in the literature for the prediction of this property have been reconsidered from a general perspective. The advantages of RecNN as a suitable tool for the automatization of fundamental parts of the QSPR/QSAR analysis have been highlighted. The RecNN model has been applied to the analysis of the Delta(solv)G degrees in water of 138 monofunctional acyclic organic compounds and tested on an external data set of 33 compounds. As a result of the statistical analysis, we obtained, for the predictive accuracy estimated on the test set, correlation coefficient R = 0.9985, standard deviation S = 0.68 kJ mol(-1), and mean absolute error MAE = 0.46 kJ mol(-1). The inherent ability of RecNN to abstract chemical knowledge through the adaptive learning process has been investigated by principal components analysis of the internal representations computed by the network. It has been found that the model recognizes the chemical compounds on the basis of a nontrivial combination of their chemical structure and target property.

Total structure determination of apratoxin A, a potent novel cytotoxin from the marine cyanobacterium Lyngbya majuscula.

Apratoxin A (1), a potent cytotoxin with a novel skeleton, has been isolated from the marine cyanobacterium Lyngbya majuscula Harvey ex Gomont. This cyclodepsipeptide of mixed peptide-polyketide biogenesis bears a thiazoline ring flanked by polyketide portions, one of which possesses an unusual methylation pattern. Its gross structure has been elucidated by spectral analysis, including various 2D NMR techniques. The absolute configurations of the amino acid-derived units were determined by chiral HPLC analysis of hydrolysis products. The relative stereochemistry of the new dihydroxylated fatty acid unit, 3,7-dihydroxy-2,5,8,8-tetramethylnonanoic acid, was elucidated by successful application of the J-based configuration analysis originally developed for acyclic organic compounds using carbon-proton spin-coupling constants ((2,3)J(C,H)) and proton-proton spin-coupling constants ((3)J(H,H)); its absolute stereochemistry was established by Mosher analysis. The conformation of 1 in solution was mimicked by molecular modeling, employing a combination of distance geometry and restrained molecular dynamics. Apratoxin A (1) possesses IC(50) values for in vitro cytotoxicity against human tumor cell lines ranging from 0.36 to 0.52 nM; however, it was only marginally active in vivo against a colon tumor and ineffective against a mammary tumor.

Predictions of thermodynamic properties at infinite dilution of aqueous organic species at high temperatures via functional group additivity

In this study, a functional group additivity scheme was used for correlation of the partial molar volumes, V 2 0, compressibilities, κ 2 0, heat capacities, C P,2 0, hydration enthalpies, Δ hyd H 2 0, and hydration Gibbs energies, Δ hyd G 2 0, at infinite dilution of aqueous organic electrolytes and non-electrolytes. The results were used for predicting the chemical potentials of these solutes. At present, the groups included are C (hydrocarbon), H (hydrocarbon), COOH, CONH 2, NH 2, OH, COO −, NH 3 +, and an amino acid functional group. An equation of state based on the Fluctuation Solution Theory was employed which allows predictions for numerous acyclic organic compounds composed of these functional groups to 623 K and 100 MPa. Although the uncertainty normally associated with a group additivity scheme is larger than the experimental uncertainty at ambient conditions, at high temperatures and pressures the two uncertainties become comparable. The functional group contributions were based on almost 1400 experimental points and are reported as a function of solvent density and temperature.

Stereochemical Determination of Acyclic Structures Based on Carbon-Proton Spin-Coupling Constants. A Method of Configuration Analysis for Natural Products.

A method for elucidating the relative configuration of acyclic organic compounds was developed on the basis of carbon-proton spin-coupling constants ((2,3)J(C,H)) and interproton spin-coupling constants ((3)J(H,H)). This method is based on the theory that, in acyclic systems, the conformation of adjacent asymmetric centers is represented by staggered rotamers, and their relative stereochemistry can be determined using (2,3)J(C,H) and (3)J(H,H), because the combined use of these J values enables the identification of the predominant staggered rotamer(s) out of the six possible derived from threo and erythro configurations. Detailed conformational analysis for model compounds 1-4 revealed that this method is useful in most cases for assignment of the configuration of acyclic structures occurring in natural products, in which stereogenic methine carbons are often substituted with a methyl or a hydroxy (alkoxy) group. This J-based configuration analysis was applied to the stereochemical elucidation of carboxylic acid 5 derived from zooxanthellatoxin and proven to be a practical method even for natural products with complicated structures.

Stereocontrol between Remote Atom Centers in Acyclic Substrates. Anti Addition of Hydride to 1,5-, 1,6-, and 1,7-Hydroxy Ketones

For conformationally unconstrained, acyclic organic compounds, the control of stereogenic centers at remote positions of a chain, that is, at a distance of four or more atom centers, remains a challenging problem in asymmetric synthesis. We report on our studies of 1,5, 1,6, and 1,7 diastereoselectivity in hydride reductions of acyclic hydroxy amino ketones and related compounds, which were sparked by our discovery of high 1,5 diastereocontrol (>10:1) with substrates such as 17 and 23. We have been able to achieve both high 1,5- and 1,6-anti diastereocontrol in the reduction of 1,5- and 1,6-hydroxy ketone substrates, respectively. However, the level of 1,7-anti diastereocontrol with 1,7-hydroxy ketones was only moderate. More specifically, reduction of 23 to 24 with R-alpine-hydride or Zn(BH4)2 in CH2Cl2 (predominantly) at −78 °C gave high 1,5-anti stereoselectivity (anti/syn = 10:1 or 13:1, respectively), and reduction of 34 to 35 with R-alpine-hydride (CH2Cl2) gave high 1,6-anti selectivity (anti/syn = ...

ChemInform Abstract: Novel, Metal‐Catalyzed Carbonylation of Acyclic Organic Compounds. The Regiospecific Carbonylation of N,S‐Acetals.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Novel, Metal-Catalyzed Carbonylation of Acyclic Organic Compounds. The Regiospecific Carbonylation of N,S-Acetals

The rhodium(I) complex, [Rh(CO) 2 Cl] 2 , catalyzes the regiospecific carbonylation of N,S-acetals of structural type PhCH 2 SCH 2 NR 1 R 2 to form PhCH 2 COSCH 2 NR 1 R 2 in 68-92% isolated yields. Exclusive inser- tion of carbon monoxide occurs into the other sulfur-carbon bond of RSCH(Ph)NR 3 R 4 (R=PhCH 2 , n-C 11 H 23 ) affording RSCOCH(Ph)NR 3 R 4 in 46-83% yield

Estimation of Properties of Acyclic Organic Compounds Using Conjugation Operators

The ABC approach to the estimation of thermodynamic and physical properties of organic compounds is based on the contributions of Atoms and Bonds in the properties of Conjugate forms of a molecular structure. The method has successfully been applied to the estimation of properties of acyclic hydrocarbons. The approach is extended to the estimation of thermodynamic and physical properties of acyclic organic compounds which may contain nitrogen, oxygen, or sulfur. The estimated properties are standard enthalpy of formation, normal boiling point, standard enthalpy of vaporization, critical pressure, critical temperature, and critical volume. The ABC technique is more accurate than a typical group-contribution approach

Computational Identification of Conjugate Paths for Estimation of Properties of Organic Compounds

Abstract We have developed and implemented a computer-based method to generate and enumerate all conjugate forms of acyclic organic compounds. These algorithms are used in a new approach for the estimation of thermodynamic and physical properties of acyclic organic compounds from their molecular structure. The approach is based on the contributions of Atoms and Bonds in the properties of Conjugate forms (ABC) of a compound and has produced more accurate results than group-contribution methods. Generating all conjugate forms of the molecule whose properties we wish to estimate is necessary in the application of this technique. The use of symbolic computing environments allows the flexible representation and manipulation of molecular structures. Atoms, bonds, molecules, and other entities are represented as interconnected objects. The generation, comparison, and analysis of conjugates are carried out through computer-based manipulation of the objects and their interconnections.

An expert system for inferring structures of organic compounds from their mass spectra

Development of an 'expert system' for elucidation of structures of acyclic organic compounds is described. An expert system is a computer program that embodies some of the heuristic problem-solving knowledge of human experts so that it can effectively be used as an aid to decision making. The expert system described in this paper is intended to assist a chemist in arriving at plausible structures, the input data being the mass spectrum, molecular formula and presence (if known) of functional groups. The program generates chemically possible structures for the given molecular formula and can use, where available, the constraints imposed by the mass spectrum of the compound and by any known functional groups. The program makes use of a new algorithm for obtaining a canonical representation of structures and a new heuristic for incorporating constraints of the mass spectrum. This work constitutes a case study of the application of artificial intelligence techniques in chemistry and the material presented highlights this motivation.