Exploiting enzymatic regioselectivity: a facile methodology for the synthesis of polyhydroxylated hybrid compounds

How Can Deep Eutectic Systems Promote Greener Processes in Medicinal Chemistry and Drug Discovery?

Chemists in the medicinal chemistry field are constantly searching for alternatives towards more sustainable and eco-friendly processes for the design and synthesis of drug candidates. The pharmaceutical industry is one of the most polluting industries, having a high E-factor, which is driving the adoption of more sustainable processes not only for new drug candidates, but also in the production of well-established active pharmaceutical ingredients. Deep eutectic systems (DESs) have emerged as a greener alternative to ionic liquids, and their potential to substitute traditional organic solvents in drug discovery has raised interest among scientists. With the use of DESs as alternative solvents, the processes become more attractive in terms of eco-friendliness and recyclability. Furthermore, they might be more effective through making the process simpler, faster, and with maximum efficiency. This review will be focused on the role and application of deep eutectic systems in drug discovery, using biocatalytic processes and traditional organic chemical reactions, as new environmentally benign alternative solvents. Furthermore, herein we also show that DESs, if used in the pharmaceutical industry, may have a significant effect on lowering production costs and decreasing the impact of this industry on the quality of the environment.

Anti-Aβ42 Aggregative Polyketides from the Antarctic Psychrophilic Fungus Pseudogymnoascus sp. OUCMDZ-3578

Seven new polyketides, diphenyl ketone (1), diphenyl ketone glycosides (2-4), diphenyl ketone-diphenyl ether dimer (6), and anthraquinone-diphenyl ketone dimers (7 and 8), together with compound 5, were isolated from the psychrophilic fungus Pseudogymnoascus sp. OUCMDZ-3578 fermented at 16 °C and identified by spectroscopic analysis. The absolute configurations of 2-4 were determined by acid hydrolysis and 1-phenyl-3-methyl-5-pyrazolone precolumn derivatization. The configuration of 5 was first determined by X-ray diffraction analysis. Compounds 6 and 8 showed the highest activity against amyloid beta (Aβ₄₂) aggregation with half-maximal inhibitory concentrations (IC₅₀) of 0.10 and 0.18 μM, respectively. They also showed strong abilities to chelate with metal ions, especially iron, were sensitive to Aβ₄₂ aggregation induced by metal ions, and displayed depolymerizing activity. Compounds 6 and 8 show potential as leads for the treatment of Alzheimer's disease to prevent Aβ₄₂ aggregation.

Combination of Enzymes and Deep Eutectic Solvents as Powerful Toolbox for Organic Synthesis

During the last decade, a wide spectrum of applications and advantages in the use of deep eutectic solvents for promoting organic reactions has been well established among the scientific community. Among these synthetic methodologies, in recent years, various examples of biocatalyzed processes have been reported, making use of eutectic mixtures as reaction media, as an improvement in terms of selectivity and sustainability. This review aims to show the newly reported protocols in the field, subdivided by reaction class as a 'toolbox' guide for organic synthesis.

Thiol-ene enabled preparation of S-lipidated anti-HBV peptides

Despite significant efforts made towards treatments for Hepatitis B virus (HBV), a long-term curative treatment has thus far eluded scientists. Recently, the Sodium Taurocholate Co-Transporting Polypeptide (NTCP) receptor has been identified as the entry pathway of HBV into hepatocytes. Myrcludex B, an N-terminally myristoylated 47-mer peptide mimic of the preS1 domain of the Hepatitis B virion, was identified as a potent protein-protein interaction (PPI) inhibitor blocking HBV fusion (IC50 = 140 pM). Herein we report an optimised chemical synthesis of Myrcludex B and a series of novel analogues. Employing a small modification to the Cysteine Lipidation of a Peptide or Amino acid (CLipPA) thiol-ene reaction, a library of S-lipidated Myrcludex B and truncated (21-mer) analogues were prepared, providing novel chemical space to probe for the discovery of novel anti-HBV peptides. The S-lipidated analogues showed an equivalent or a slight decrease (∼2-fold) in binding effectiveness to NTCP expressing hepatocytes compared to Myrcludex B. Three S-lipidated analogues were highly potent HBV inhibitors (IC50 0.97-3.32 nM). These results demonstrate that incorporation of heteroatoms into the lipid 'anchor' is tolerated by this antiviral scaffold and to the best of our knowledge constitutes the first report of potent S-lipidated antiviral peptides. Interestingly, despite only moderate reductions in binding effectiveness, truncated analogues possessed dramatically reduced inhibitory activity thus providing new insights into the structure activity relationship of these hitherto unreported antiviral S-lipopeptides.

Synthesis of Lipopeptides by CLipPA Chemistry

Lipidation of polypeptides with a fatty acid to form N-linked lipopeptides can be a time consuming process due to the need to mask other reactive function groups present on the side chains of amino acids. Cysteine Lipidation on a Peptide or Amino acid (CLipPA) technology enables the direct lipidation of unprotected peptides containing a free thiol group to afford S-lipidated lipopeptides. A generalized procedure for the synthesis of S-lipopeptides is described which facilities rapid preparation of tens of analogs of lipopeptides from a single thiolated polypeptide precursor.

Variable-Length Ester-Based Staples for α-Helical Peptides by Using A Double Thiol-ene Reaction

A novel peptide stapling method effected by a double thiol-ene reaction between two cysteine residues and a divinyl diester to access stapled peptides with enhanced cell permeability is reported. This diverse chemical tool kit provides facile access to stapled peptides with varying bridge lengths. Stapled Axin mimetics were synthesised by using this stapling method resulting in improved α-helicity relative to the unstapled peptide. Cell penetrating stapled analogues of the SIGK peptide that targets the protein-protein interaction hotspot of Gβγ proteins were also synthesised that exhibited a moderate increase in α-helicity and were cell permeable. This chemoselective peptide stapling method is highly amenable as a facile method to easily modify synthetic α-helical peptides to target intracellular proteins.

Synthesis of Antimicrobial Lipopeptides Using the "CLipPA" Thiol-Ene Reaction

Cysteine Lipidation on a Peptide or Amino acid (CLipPA) technology provides a facile method for the lipidation of unprotected peptides containing a free thiol group by using a "click" radical-initiated thiol-ene reaction to effect addition to a vinyl ester. The methodology is highly versatile, leading to high conversion rates while maintaining excellent chemoselectivity and tolerance for a large variety of peptide substrates and functional groups. Herein we describe the simple general procedure for the synthesis of a focused library of bioactive S-lipidated antimicrobial peptides via late-stage derivatization using solution-phase CLipPA lipidation.

Isoquercitrin Esters with Mono- or Dicarboxylic Acids: Enzymatic Preparation and Properties

A series of isoquercitrin (quercetin-3-O-β-d-glucopyranoside) esters with mono- or dicarboxylic acids was designed to modulate hydro- and lipophilicity and biological properties. Esterification of isoquercitrin was accomplished by direct chemoenzymatic reaction using Novozym 435 (lipase from Candida antarctica), which accepted C₅- to C12-dicarboxylic acids; the shorter ones, such as oxalic (C₂), malonic (C₃), succinic (C₄) and maleic (C₄) acids were not substrates of the lipase. Lipophilicity of monocarboxylic acid derivatives, measured as log P, increased with the chain length. Esters with glutaric and adipic acids exhibited hydrophilicity, and the dodecanedioic acid hemiester was more lipophilic. All derivatives were less able to reduce Folin-Ciocalteau reagent (FCR) and scavenge DPPH (1,1-diphenyl-2-picrylhydrazyl) than isoquercitrin; ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) radical-scavenging activity was comparable. Dodecanoate and palmitate were the least active in FCR and ABTS scavenging; dodecanoate and hemiglutarate were the strongest DPPH scavengers. In contrast, most derivatives were much better inhibitors of microsomal lipoperoxidation than isoquercitrin; butyrate and hexanoate were the most efficient. Anti-lipoperoxidant activity of monocarboxylic derivatives, except acetates, decreased with increasing aliphatic chain. The opposite trend was noted for dicarboxylic acid hemiesters, isoquercitrin hemidodecanedioate being the most active. Overall, IQ butyrate, hexanoate and hemidodecanedioate are the most promising candidates for further studies.

An update of biocatalytic selective acylation and deacylation of monosaccharides

PAMs synthesis requires highly selective reactions, provided by hydrolases. This review updates research on enzymatic acylation and deacylation of monosaccharides, focusing on synthetic useful PAMs and drug-monosaccharide conjugates involving PAMs.

Dicarboxylic esters: Useful tools for the biocatalyzed synthesis of hybrid compounds and polymers

Dicarboxylic acids and their derivatives (esters and anhydrides) have been used as acylating agents in lipase-catalyzed reactions in organic solvents. The synthetic outcomes have been dimeric or hybrid derivatives of bioactive natural compounds as well as functionalized polyesters.

Chemo-enzymatic synthesis of silybin and 2,3-dehydrosilybin dimers

Divalent or multivalent molecules often show enhanced biological activity relative to the simple monomeric units. Here we present enzymatically and chemically prepared dimers of the flavonolignans silybin and 2,3-dehydrosilybin. Their electrochemical behavior was studied by in situ and ex situ square wave voltammetry. The oxidation of monomers and dimers was similar, but adsorption onto the electrode and cell surfaces was different. A 1,1-diphenyl-2-picrylhydrazyl (DPPH) and an inhibition of microsomal lipoperoxidation assay were performed with same trend of results for silybin and 2,3-dehydrosilybin dimers. Silybin dimer showed better activity than the monomer, while on the contrary 2,3-dehydrosilybin dimer presented weaker antioxidant/antilipoperoxidant activity than its monomer. Cytotoxicity was evaluated on human umbilical vein endothelial cells, normal human adult keratinocytes, mouse fibroblasts (BALB/c 3T3) and human liver hepatocellular carcinoma cell line (HepG2). Silybin dimer was more cytotoxic than the parent compound and in the case of 2,3-dehydrosilybin its dimer showed weaker cytotoxicity than the monomer.