Category: Chemistry

Properties of octenyl succinic anhydride (OSA) modified starches and their application in low fat mayonnaise

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Wheat starch (WS), corn starch (CS), waxy corn starch (WCS), potato starch (PS), sweet potato (SP), rice starch (RS) and kidney bean (KB) were modified using octenyl succinic anhydride (OSA) and evaluated for various properties. Degree of substitution (DS) showed significant increase with increase in amylose (AM) content. OSA modified starches showed higher paste viscosities compared to their native counterparts. OSA groups acted majorly on the surface and caused some superficial pores, but crystalline pattern was not significantly altered for all starches. OSA modified starches were used in preparing low fat mayonnaise by substituting 75% fat. OSA modified starches enhanced the emulsifying properties of mayonnaise. Mayonnaises prepared using OSA modified starches were evaluated for phase separation, brightness (L*), color index (dE), and rheological parameters (G′ and G″). Mayonnaises prepared using OSA modified starches showed higher G’ and exhibited gel like structure. Fat substituted (FS) mayonnaise was preferred over full fat (FF) mayonnaise by the consumers. No significant effect of fat substitution was observed on particle size and phase separation for all mayonnaise samples. (International Journal of Biological Macromolecules.,Volume 131, 15 June 2019, Pages 147-157.)

A Novel Antimicrobial-Phytochemical Conjugate With Antimicrobial Activity Against Streptococcus uberis, Enterococcus faecium, and Enterococcus faecalis

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Antimicrobial resistance is one of the major threats to human and animal health. An effective strategy to reduce and/or delay antimicrobial resistance is to use combination therapies. Research in our laboratory has been focused on combination therapies of antimicrobials and phytochemicals and development of antimicrobial-phytochemical conjugates. In this study, we report the synthesis and antimicrobial activity of a novel sulfamethoxazole-gallic acid conjugate compound (Hybrid 1). Hybrid 1 not only showed much stronger activity than sulfamethoxazole towards Streptococcus uberis 19436, Enterococcus faecium 700221, and Enterococcus faecalis 29212, which were purchased from American Type Culture Collection (ATCC), but also exhibited a promising antimicrobial effect against two E. faecalis clinical isolates, one of which was multidrug-resistant. Further studies are warranted to establish the in vivo antimicrobial activity for Hybrid 1 and develop more potent sulfamethoxazole-gallic acid-based antimicrobial conjugates using hybrid 1 as a lead compound. (Front Pharmacol. 2019 Nov 28;10:1405.)

A Phytochemical-Based Copolymer Derived from Coriolus versicolor Polysaccharopeptides for Gene Delivery

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Coriolus versicolor is an herb widely used for cancer treatment in traditional Chinese medicine. Its active ingredients, polysaccharopeptides (PSP), have been used for adjuvant therapies in cancer treatment. This study conjugates Coriolus versicolor PSP with poly(ethylenimine) (PEI) to generate a PSP-PEI copolymer for gene transfer. After PEI conjugation, both the pH buffering capacity and DNA compaction ability of PSP are significantly increased. Compared with that of PSP, the transfection efficiency of PSP-PEI is 10 to 20-fold higher in vitro. This is a proof-of-concept study reporting the direct use of bioactive phytochemicals from traditional Chinese medicine for gene vector development. The promising performance of PSP-PEI raises the possibility that bioactive herbal ingredients can be further developed as a multi-therapeutic gene carrier for tackling cancers.

C. versicolor PSP are water-soluble substances having a dark brown colour and characteristic odour. Their polysaccharide moieties are highly complex, consisting of glucose molecules linked with different sugar units (e.g., galactose, mannose, arabinose, and xylose); whereas the peptide moieties contain a large amount of aspartic acid and glutamic acid, with acidic and neutral amino acids (such as leucine, glycine, alanine, threonine, serine, glutamic acid, valine and aspartic acid) accounting for 70% of all kinds of amino acids present. PEI is a cationic aziridine polymer that exists as a polycation showing high pH buffering capacity over a broad range of pH values. Previous studies have revealed that the transfection efficiency and cytotoxicity of PEI are positively related to the molecular weight of PEI. As the aim of PEI incorporation in this study is to enhance the positive charge density of PSP, LMW PEI (e.g., PEI 0.8K) is adopted because it can serve the purpose and is less toxic than its high-molecular-weight counterparts. During synthesis, 1,1′-carbonyldiimidazole (CDI), which activates the hydroxyl groups of PSP to form active imidazolyl carbamate intermediates, is used as a coupling agent. The intermediates are subsequently attacked by the primary amine groups of PEI to form PSP-PEI, with imidazole being released as a byproduct. (Molecules. 2018 Sep 6;23(9):2273.)

An efficient deprotection method for 5′-[O,O-bis(pivaloyloxymethyl)]-(E)-vinylphosphonate containing oligonucleotides

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5′-(E)-Vinylphosphonate (VP) is an effective bioisostere of the natural 5′-monophosphate in small interfering RNAs (siRNAs). Solid-phase synthesis of VP-siRNAs requires the use of appropriately protected VP-phosphoramidites in combination with optimal oligonucleotide deprotection conditions. Addition of 3% (v) neat diethylamine to the standard aqueous ammonia deprotection conditions allows clean and rapid one-step deprotection of 5′-[O,O-bis(pivaloyloxymethyl)] (POM)-protected VP oligonucleotides, minimizing side reactions and impurities, which broadly enhances the scope of VP oligonucleotide synthesis. (Tetrahedron.Volume 74, Issue 42, 18 October 2018, Pages 6182-618.)

Chemical ligation of oligonucleotides using an electrophilic phosphorothioester

We developed a new approach for chemical ligation of oligonucleotides using the electrophilic phosphorothioester (EPT) group. A nucleophilic phosphorothioate group on oligonucleotides was converted into the EPT group by treatment with Sanger’s reagent (1-fluoro-2,4-dinitrobenzene). EPT oligonucleotides can be isolated, stored frozen, and used for the ligation reaction. The reaction of the EPT oligonucleotide and an amino-modified oligonucleotide took place without any extra reagents at pH 7.0–8.0 at room temperature, and resulted in a ligation product with a phosphoramidate bond with a 39–85% yield. This method has potential uses in biotechnology and chemical biology. (Nucleic Acids Res. 2017 Jul 7; 45(12): 7042–7048.)

Fragment-based solid-phase assembly of oligonucleotide conjugates with peptide and polyethylene glycol ligands

Ligand conjugation to oligonucleotides is an attractive strategy for enhancing the therapeutic potential of antisense and siRNA agents by inferring properties such as improved cellular uptake or better pharmacokinetic properties. Disulfide linkages enable dissociation of ligands and oligonucleotides in reducing environments found in endosomal compartments after cellular uptake. Solution-phase fragment coupling procedures for producing oligonucleotide conjugates are often tedious, produce moderate yields and reaction byproducts are frequently difficult to remove. We have developed an improved method for solid-phase coupling of ligands to oligonucleotides via disulfides directly after solid-phase synthesis. A 2′-thiol introduced using a modified nucleotide building block was orthogonally deprotected on the controlled pore glass solid support with N-butylphosphine. Oligolysine peptides and a short monodisperse ethylene glycol chain were successfully coupled to the deprotected thiol. Cleavage from the resin and full removal of oligonucleotide protection groups were achieved using methanolic ammonia. After standard desalting, and without further purification, homogenous conjugates were obtained as demonstrated by HPLC, gel electrophoresis, and mass spectrometry. The attachment of both amphiphilic and cationic ligands proves the versatility of the conjugation procedure. An antisense oligonucleotide conjugate with hexalysine showed pronounced gene silencing in a cell culture tumor model in the absence of a transfection reagent and the corresponding ethylene glycol conjugate resulted in down regulation of the target gene to nearly 50% after naked application.(European Journal of Medicinal Chemistry.,Volume 121, 4 October 2016, Pages 132-142.)

Solid-phase synthesis of 5′-triantennary N-acetylgalactosamine conjugated antisense oligonucleotides using phosphoramidite chemistry

A convenient solid-phase synthetic method was developed for assembling a triantennary N-acetylgalactosamine (GalNAc) cluster on the 5′-end of antisense oligonucleotide using phosphoramidite chemistry. Conjugation of the 5′-triantennary GalNAc cluster improved potency of the 14 mer ASO 7-fold in mice and more than 50 fold in hepatocytes. The synthetic approach described in this Letter simplifies the synthesis of 5′-triantennary GalNAc cluster conjugated ASOs and helps understand the structure–activity relationship for targeting hepatocytes with oligonucleotide therapeutics.(Bioorganic & Medicinal Chemistry Letters.,Volume 25, Issue 19, 1 October 2015, Pages 4127-4130.)