GIAO NMR shift calculation has been applied to the challenging task of reliably assigning stereochemistry with quantifiable confidence when only one set of experimental data are available. We have compared several approaches for assigning a probability to each candidate structure and have tested the ability of these methods to distinguish up to 64 possible diastereoisomers of 117 different molecules, using NMR shifts obtained in rapid and computationally inexpensive single-point calculations on molecular mechanics geometries without time-consuming ab initio geometry optimization. We show that a probability analysis based on the errors in each 13C or 1H shift is significantly more successful at making correct assignments with high confidence than are probabilities based on the correlation coefficient and mean absolute error parameters. Our new probability measure, which we have termed DP4, complements the probabilities obtained from our previously developed CP3 parameter, which applies to the case of assig...

Assigning Stereochemistry to Single Diastereoisomers by GIAO NMR Calculation: The DP4 Probability

GIAO NMR chemical shifts have been calculated for a set of 28 pairs of diastereoisomers in order to test the ability of NMR shift calculation to distinguish between diastereomeric structures. We compare the performance of several different parameters for quantifying the agreement between calculated and experimental shifts from the point of view of assigning structures and introduce a new parameter, CP3, based on comparing differences in calculated shift with differences in experimental shift, which is significantly more successful at making correct structure assignments with high confidence than are the currently used parameters of the mean absolute error and the correlation coefficient. Using our new parameter in conjunction with Bayes’ theorem, stereostructure assignments can be made with quantifiable confidence using shifts obtained in single point calculations on molecular mechanics geometries without computationally expensive ab initio geometry optimization.

Assigning the stereochemistry of pairs of diastereoisomers using GIAO NMR shift calculation.

Thiazoles, oxazole and their corresponding reduced derivatives, thiazolines and oxazolines, are found in marine sources exhibiting significant biological activities. The isolation, synthetic, and biological studies of these natural products, covering literature from January 2007 to June 2010, are summarized.

https://www.mdpi.com/1660-3397/8/11/2755/pdf

Thiazole and Oxazole Alkaloids: Isolation and Synthesis

For over 40 years, small organic molecules derived naturally from microbes and plants have provided a number of useful cancer chemotherapeutic drugs. The search for naturally occurring lead compounds of this type has continued in recent years, with the constituents of marine fauna and flora as well as those of terrestrial microorganisms and plants being investigated for their anti-cancer activities. In the present short review, selected new compounds or their derivatives are described that have obtained for the first time recently from organisms of diverse biological origin, with potential use as cancer chemotherapeutic agents. It may be seen that such promising lead compounds tend to rapidly generate considerable interest among scientists such as synthetic organic chemists and biologists. Consequently, the supply of a given precious natural product sample may be enhanced, and it may be possible to determine a preliminary notion of structure-activity relationships and of its potential mechanism of action.

Discovery of natural product anticancer agents from biodiverse organisms.

This review focuses on the methodology used for the construction of tetrahydropyran (THP) rings in the synthesis of natural products over the last seven years. While methods like cyclisation onto oxocarbenium ions, reduction of cyclic hemi-ketals, Michael reactions, hetero-Diels–Alder cycloadditions and cyclisations onto epoxides continue to find application, several other strategies including metal-mediated cyclisations, ring-closing metathesis, radical cyclisations and carbocation cyclisations have also found use. This review is intended to provide an overview of the area for those who are unfamiliar, and to refresh and remind those who do work in the area of the exciting developments in the field.

Strategies for the construction of tetrahydropyran rings in the synthesis of natural products

Total Synthesis and Stereochemical Reassignment of (+)‐Neopeltolide

Total Synthesis and Stereochemical Reassignment of (+)‐Neopeltolide.

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Total Synthesis and Stereochemical Reassignment of (+)‐Neopeltolide

Total Synthesis and Stereochemical Reassignment of (+)‐Neopeltolide.