A Tyrosinase Inhibitor from a Nitrogen-Enriched Chemically Engineered Extract.

The enzyme tyrosinase is involved in the biosynthesis of melanin and the enzymatic browning of fruits and vegetables, and therefore, its inhibitors have potential to treat hyperpigmentary disorders or to function as food antibrowning agents. The use of hydrazine monohydrate as a reagent to prepare chemically engineered extracts can lead to semisynthetic compounds that contain the portion N-N, a fragment rarely found in natural products and present in some tyrosinase inhibitors. Here, we report the tyrosinase inhibition screening of a series of chemically engineered extracts that are diversified by reaction with hydrazine. LC-MS was used to evaluate the change in composition produced by the reaction. Bioguided fractionation of the most active chemically engineered extract, prepared from Matricaria recutita L., led to the discovery of a pyrazole that inhibits tyrosinase with an IC50 value of 28.20 ± 1.13 µM. This compound was produced by a one-pot double chemical transformation of its natural precursor, which includes an unexpected selective removal of one -OH group.

A Bioactive Trypanosoma cruzi Bromodomain Inhibitor from Chemically Engineered Extracts.

A set of chemically engineered extracts enriched in compounds including N-N and N-O fragments in their structures was prepared. Bromodomain binding screening and bioguided fractionation led to the identification of one oxime hit that interacts with TcBDF3 with affinity in the submicromolar range and that shows interesting antiparasitic properties against the different life cycle stages of T. cruzi.

Reverse Phase Compatible TLC-Bioautography for Detection of Tyrosinase Inhibitors.

INTRODUCTION: Reverse phase chromatography and bioautographic assays are key tools for natural product bioguided isolation; however, their direct coupling has not been fully achieved. OBJECTIVES: To develop a bioautographic assay to detect tyrosinase inhibitors present in complex matrices sorbed on reverse phase (RP) TLC-plates that can be used for bioguided isolation of bioactive compounds. METHODS: Enzyme gel entrapment with an amphiphilic copolymer was used for assay development. The gel turns into a brown "skin like" colour due to tyrosinase catalysed oxidation of l-tyrosine. The inhibitors are visualised as clear spots against a brown coloured background. RESULTS: The assay was able to localise cinnamaldehyde in Cinnamomum cassia essential oil, as its main constituent with known tyrosinase inhibition properties. The assay allowed the detection of 0.03% (w/w) of kojic acid co-spotted with a methanolic extract of Sphaeralcea bonariensis and chromatographed on RP-TLC. CONCLUSION: The developed assay is able to detect, with high sensitivity, tyrosinase inhibitors present in complex matrices that were chromatographed in RP-TLC. Results can be easily read by colour change, inhibitors appear as clear spots in a darker background. Copyright © 2016 John Wiley & Sons, Ltd.

Discovery of ß-glucosidase inhibitors from a chemically engineered extract prepared through ethanolysis.

A series of vegetal extracts have been chemically altered by ethanolysis. The effect of the reaction on the inhibition of the enzyme ß-glucosidase properties of the mixtures was studied using thin layer chromatography (TLC) with biodetection. Glucosidase inhibitory activity guided fractionation of one of the produced chemically engineered extracts led to the isolation of apigenin and ethyl p-cumarate. Both compounds were generated during the chemical modification step.

Chemically engineered extracts: source of bioactive compounds.

Biological research and drug discovery critically depend on access to libraries of small molecules that have an affinity for biomacromolecules. By virtue of their sustained success as sources of lead compounds, natural products are recognized as "privileged" starting points in structural space for library development. Compared with synthetic compounds, natural products have distinguishing structural properties; indeed, researchers have begun to quantify and catalog the differences between the two classes of molecules. Measurable differences in the number of chiral centers, the degree of saturation, the presence of aromatic rings, and the number of the various heteroatoms are among the chief distinctions between natural and synthetic compounds. Natural products also include a significant proportion of recurring molecular scaffolds that are not present in currently marketed drugs: the bioactivity of these natural substructures has been refined over the long process of evolution. In this Account, we present our research aimed at preparing libraries of semisynthetic compounds, or chemically engineered extracts (CEEs), through chemical diversification of natural products mixtures. The approach relies on the power of numbers, that is, in the chemical alteration of a sizable fraction of the starting complex mixture. Major changes in composition can be achieved through the chemical transformation of reactive molecular fragments that are found in most natural products. If such fragments are common enough, their transformation represents an entry point for chemically altering a high proportion of the components of crude natural extracts. We have searched for common reactive fragments in the Dictionary of Natural Products (CRC Press) and identified several functional groups that are expected to be present in a large fraction of the components of an average natural crude extract. To date, we have used reactions that incorporate (i) nitrogen atoms through carbonyl groups, (ii) sulfur by transformation of -OH and amines, and (iii) bromine through double bonds and aromatic rings. The resulting CEEs had different composition and biomolecular properties than their natural progenitors. We isolated a semisynthetic ß-glucosidase inhibitor from a CEE prepared by reaction with benzenesulfonyl chloride, an antifungal pyrazole from a CEE prepared by reaction with hydrazine, and an acetylcholinesterase inhibitor from a CEE prepared through bromination. Our results illustrate how biological activity can be generated through chemical diversification of natural product mixtures. Moreover, the level of control that can be asserted in the process by judicious design and experimental choices underscores the potential for further development of CEEs in both basic research and drug discovery.

Brominated extracts as source of bioactive compounds.

The chemical composition and the biomolecular properties of a crude plant extract were altered through bromination leading to the discovery of an acetylcholinesterase inhibitor.

Chemically engineered extracts: bioactivity alteration through sulfonylation.

The chemical composition and the biomolecular properties of a series of crude plant extracts were altered without previous knowledge of their detailed chemical composition.