Computer-assisted structure elucidation

Summary Program CASE, an evolving computer model of the structure elucidation process, treats three major tasks: reduction of the chemical and spectral properties of a compound of unknown structure to their structural implications, generation of all complete molecular structures compatible with the structural features identified, and ranking these structures on the basis of the degree of fit between predicted and observed spectral properties. The current program status is described and program application is illustrated.

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Strukturaufklärung mit Computer-Hilfe

Zusammenfassung Ein in Entwicklung befindliches Computer-Modell (program CASE) wird beschrieben, das hauptsächlich folgende drei Aufgaben erfüllt: Zuordnung der chemischen und spektralen Eigenschaften einer Verbindung unbekannter Struktur zu ihren strukturellen Bedeutungen; Aufstellung aller Strukturen, die mit den gefundenen Eigenschaften im Einklang stehen; Einordnung dieser Strukturen je nach Übereinstimmung mit den vorhergesagten und gefundenen Parametern. Der derzeitige Entwicklungsstand des Programms wird erläutert und die Anwendung diskutiert.

     

Novel methods of automated structure elucidation based on 13C NMR spectroscopy

Three new approaches for automated structure elucidations of organic molecules using NMR spectroscopic data were introduced recently. These approaches apply a neural network 13C NMR chemical shift prediction method to rank the results of structure generators by their agreement of the predicted and experimental chemical shifts. These three existing implementations are compared using realistic example molecules. The applicability and reliability of such approaches is addressed.     

Computer assisted structure elucidation

Program case, an evolving computer model of the structure elucidation process, treats three major tasks: reduction of chemical and spectral properties to their structural implications, generation of complete molecular structures compatible with the structural features identified, and ranking these structures by comparing predicted and observed spectral properties. Current program status and application will be discussed.

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Strukturaufklärung mit Computer-Hilfe

     

New computer-assisted methods for the elucidation of molecular structure from 2-D spectra

General principles of the construction of expert systems for the elucidation of the structure of molecules from their spectra were considered. The principal attention was focused on systems based on the use of 2-D NMR spectra. The structural information extracted from 2D NMR spectra was characterized, and the strategy was outlined for structure elucidation under the conditions when the analyzed spectrostructural information is incomplete, fuzzy, and contradictory. The most advanced expert system ACD/Structure Elucidator, which is capable of determining the structure and stereochemistry of large molecules, in particular, those typical in the chemistry of natural compounds, is described as an example.     

Isolation and structure elucidation of ovalicin

The structure of ovalicin, a metabolite of the fungus Pseudeurotium ovalis with immunosuppressive activity, has been determined to be 11 .     

Evolutionary-algorithm-based strategy for computer-assisted structure elucidation

An evolutionary algorithm (EA) using a graph-based data structure to explore the molecular constitution space is presented. The EA implementation proves to be a promising alternative to deterministic approaches to the problem of computer-assisted structure elucidation (CASE). While not relying on any external database, the EA-guided CASE program SENECA is able to find correct solutions within calculation times comparable to that of other CASE expert systems. The implementation presented here significantly expands the size limit of constitutional optimization problems treatable with evolutionary algorithms by introducing novel efficient graph-based genetic operators. The new EA-based search strategy is discussed including the underlying data structures, component design, parameter optimization, and evolution process control. Typical structure elucidation examples are given to demonstrate the algorithm's performance.     

Computer methods of structure elucidation by1H and13C NMR spectra using factographic databanks

Computer methods have been developed for structure elucidation by ¹ H and ¹³ C NMR spectra using factographic databanks containing spectral and structural data of many organic compounds (44,000 for ¹ H NMR and 27,000 for ¹³ C NMR). Information about the structure of compounds under study is obtained from the analysis of reference structures whose spectra are the best matches of the query spectra. This procedure identifies linked fragments composed of the nodes assigned to signals of the query spectrum when comparing it with reference spectra, and of inactive nodes separated from the former by one bond at most. Using many examples, it has been shown that this approach allows one to determine sufficiently large structural fragments of unknowns both by ¹ H and ¹³ C NMR spectra. The most reliable structures are obtained from the combined analysis of ¹ H and ¹³ C NMR spectral search results. Thus the relative occurrences of correct fragments among the n-first (n=1, 3, 5) fragments of the ranked list of candidates, output to the user, are 80, 93, and 96%, respectively.Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 3, pp. 51–60, May–June 1993.Translated by L. Smolina     

Isolation and structure elucidation of 11-desacetoxywortmannin

The structure of 11-desacetoxy-wortmannin ( 3 ), a new antiinflammatory metabolite of the fungus Penicillium funiculosum THOM, has been elucidated by physico-chemical methods and chemical correlation with wortmannin ( 1 ).     

Applications of a HOUDINI-based structure elucidation system

SESAMI, a comprehensive program for the elucidation of the structure of complex compounds of carbon, incorporates a structure reduction-based structure genearator (COCOA). Observed limitations with this program in the solution of higher molecular weight unknowns prompted the development of a structure generator (HOUDINI) which embodies a new concept, convergent structure generation. A comparison of the performance of COCOA-based and HOUDINI-based SESAMI using a set of complex, naturally occurring compounds as a test set of unknowns revealed faster execution times and more efficient processing of ambiguous structural information for the latter.     

Isolation and structure elucidation of ishwarol B

Ishwarol B was isolated from the bark oil of Cedrelopsis grevei and its structure elucidated by 1D and 2D NMR spectroscopy.     

Computer-aided structure elucidation of organic compounds with the chemics system: Removal of Redundant Candidates by 13C-n.m.r. Prediction

A ¹³C-n.m.r. prediction module capable of removing inappropriate candidate structures given for an unknown compound based on the spectral data is introduced for the CHEMICS system. Given a set of candidate structures generated in the system, the routine may be used to prune off redundant candidates which have a predicted number of signals inconsistent with the observed number. It is shown that the addition of the examination module to the system makes structure elucidation by computer much more practical.     

The structure elucidation of isomalyngamide K from the marine cyanobacterium Lyngbya majuscula by experimental and DFT computational methods

The 2Z-isomer of malyngamide K has been isolated along with the known compounds malyngamide C, deoxy-C and K, and characterized from a Papua New Guinea field collection of the cyanobacterium Lyngbya majuscula. The planar structure was deduced by 1D and 2D NMR spectroscopic and mass spectral data interpretation. The absolute configurations were determined on the basis of spectroscopic techniques, chemical degradation and DFT theoretical calculations.     

NMR solvent shifts and structure elucidation in coumarins

The use of the solvent shift techniques enables the position of methyl, methoxyl and aromatic protons in coumarins to be determined and should prove a valuable aid to structural elucidation in this class of compounds.     

Synthesis and structure elucidation of new cytotoxic azathioxanthones

A series of new cytotoxic azathioxanthones 7a-h was synthesized and characterized by their spectral data.     

Isolation and elucidation of the structure of homocryptolepinone

The structure of a new indolobenzazepine alkaloid, homocryptolepinone, isolated from extracts of the roots of the indigenous Ghanaian medicinal plant Cryptolepis sanguinolenta, is reported. The structure was determined using mass spectrometric, one-dimensional nOe difference nmr, and inverse-detected two-dimensional nmr experiments which included HMQC, IDR-(Inverted Direct Response)-HMQC-TOCSY, and HMBC experiments. The structure of homocryptolepinone is significant in that it may provide insight into the biogenesis of the benzpyrrolizinobenzazepine portion of the structure of the complex spiro nona-cyclic alkaloid cryptospirolepine previously isolated in these laboratories from C. sanguinolenta, and which has no precedent in alkaloid chemistry.