Relative Stereochemical Determination and Synthesis of the C1−C17 Fragment of a New Natural Polyketide

Detection of Mycolactone by Thin Layer Chromatography

By means of thin layer chromatography coupled to a fluorescence enhancer, a highly sensitive and operationally simple method to detect the mycolactones stemming from the human pathogen Mycobacterium ulcerans was developed and applied to various sample sources.

A synthesis-enabled relative configurational assignment of the C31-C46 region of hemicalide

With 21 unknown stereocentres embedded in spatially separated stereoclusters, the cytotoxic polyketide hemicalide represents a seemingly intractible structural assignment problem. Herein, through the targeted synthesis of configurationally defined fragments, as...

Secondary metabolites from Antarctic marine-derived fungus Penicillium crustosum HDN153086

A new polyene compound (1) and a new diketopiperazine (2), as well as three known compounds (3-5), were isolated from the Antarctic marine-derived fungus Penicillium crustosum HDN153086. The structures of 1-5 were deduced based on MS, NMR and TD-DFT calculations of specific ECD spectra. These compounds were evaluated for their cytotoxic activities against K562 cell line and only compound 2 exhibited cytotoxicity against K562 cell, with IC₅₀ value of 12.7 μM.

A synthesis-enabled relative stereochemical assignment of the C1-C28 region of hemicalide

Through synthesising both candidate diastereomers of a model C1-C28 fragment of the potent cytotoxic marine polyketide hemicalide, an assignment of the relative configuration between the C1-C15 and C16-C26 regions has been achieved. By detailed NMR comparisons with the natural product, the relative stereochemistry between these two 1,6-related stereoclusters is elucidated as 13,18-syn rather than the previously proposed 13,18-anti relationship. A flexible and modular strategy using an advanced C1-C28 ketone fragment 22 is outlined to elucidate the remaining stereochemical features and achieve a total synthesis.

Toward the stereochemical assignment and synthesis of hemicalide: DP4f GIAO-NMR analysis and synthesis of a reassigned C16–C28 subunit

Computational DP4f GIAO-NMR analysis resulted in a stereochemical reassignment of hemicalide, supported by improved NMR correlations with a C13–C25 fragment.

The synthesis and biological evaluation of a kabiramide C fragment modified with a WH2 consensus actin-binding motif as a potential disruptor of the actin cytoskeleton

Despite its low affinity for actin monomers, a fragment of kabiramide C disrupts actin filamentsin vitroand in cells.

Total syntheses of linear polythiazole/oxazole plantazolicin A and its biosynthetic precursor plantazolicin B

Plantazolicin A, a linear decacyclic natural product, exhibits desirable selective activity against the causative agent of anthrax toxicity. The total synthesis of plantazolicin A and its biosynthetic precursor plantazolicin B was successfully achieved by an efficient, unified, and highly convergent route featuring dicyclizations to form 2,4-concatenated oxazoles and the mild synthesis of thiazoles from natural amino acids. This report represents the first synthesis of plantazolicin B and includes the first complete characterization data for both natural products.

Assigning stereochemistry to single diastereoisomers by GIAO NMR calculation: the DP4 probability

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 (13)C or (1)H 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 assigning a pair of diastereoisomers when one has both experimental data sets. We illustrate the application of DP4 to assigning the stereochemistry or structure of 21 natural products that were originally misassigned in the literature or that required extensive synthesis of diastereoisomers to establish their stereochemistry.

Silylene-mediated polarity reversal of dienoates: additions of dienoates to aldehydes at the δ-position to form trans-dioxasilacyclononenes

Silylene transfer to α,β,γ,δ-unsaturated carbonyl compounds produced oxasilacyclopentenes that underwent thermal additions to aldehydes to produce trans-dioxasilacyclononenes as single stereoisomers. This reaction, which converts the δ-position of the unsaturated carbonyl compound into a nucleophilic center, represents an inversion of polarity from the normal pattern of reactivity. The stereospecificity of the reaction suggests that the addition to aldehydes occurred through a closed, chairlike six-membered transition state. This reaction can be used to prepare enantiomerically pure materials by the use of chiral auxiliaries to control the formation of the oxasilacyclopentenes. Functionalization of the resulting trans-cycloalkene occurred with complete stereoselectively.