Late-Stage Chemoenzymatic Installation of Hydroxy-Bearing Allyl Moiety on the Indole Ring of Tryptophan-Containing Peptides

The late-stage functionalization of indole- and tryptophan-containing compounds with reactive moieties facilitates downstream diversification and leads to changes in their biological properties. Here, the synthesis of two hydroxy-bearing allyl pyrophosphates is described. A chemoenzymatic method is demonstrated which uses a promiscuous indole prenyltransferase enzyme to install a dual reactive hydroxy-bearing allyl moiety directly on the indole ring of tryptophan-containing peptides. This is the first report of late-stage indole modifications with this reactive group

Structure-Guided Mutagenesis Reveals the Catalytic Residue that Controls the Regiospecificity of C6-Indole Prenyltransferases

Indole is a significant structural moiety and functionalization of the C−H bond in indole-containing molecules expands their chemical space, and modifies their properties and/or activities. Indole prenyltransferases (IPTs) catalyze the direct regiospecific installation of prenyl moieties on indole-derived compounds. IPTs have shown relaxed substrate flexibility enabling them to be used as tools for indole functionalization. However, the mechanism by which certain IPTs target a specific carbon position is not fully understood. Herein, we use structure-guided site-directed mutagenesis, in vitro enzymatic reactions, kinetics and structural-elucidation of analogs to verify the key catalytic residues that control the regiospecificity of all characterized regiospecific C6 IPTs. The presented results also demonstrate that substitution of PriB_His312 to Tyr leads to the synthesis of analogs prenylated at different positions than C6. This work contributes to understanding of how certain IPTs can access a challenging position in indole-derived compounds

Regiospecific Synthesis of Calcium‐Independent Daptomycin Antibiotics Using a Chemoenzymatic Method

Daptomycin (DAP) is a calcium (Ca2+)‐dependent FDA‐approved antibiotic drug for the treatment of Gram‐positive infections. It possesses a complex pharmacophore hampering derivatization and/or synthesis of analogs. In order to mimic the Ca2+‐binding effect we uses a chemoenzymatic approach to modify the tryptophan (Trp) residue of DAP and synthesize kinetically characterized and structurally elucidated regiospecific Trp‐modified DAP analogs. We demonstrated that the modified DAPs are several‐folds active than the parent molecule against antibiotic‐susceptible and antibiotic‐resistant Gram‐positive bacteria. Strikingly and in contrast to the parent molecule, the DAP derivatives do not rely on calcium or any additional elements for activity

One-Pot Tandem Approach to Functionalized 3‑Hydroxy-2-furanyl-acrylamides

A novel one-pot tandem process involving Knoevenagel condensation, Michael addition, selective amidation, and Paal–Knorr cyclization to diverse functionalized 3-hydroxy-2-furanyl-acrylamides from simple 2-oxoaldehydes and aroylacetonitriles was presented. Attempts were also made to expand the scope of the reaction to different 2-heteroarylfurans. The packing diagram of the molecules viewed down along the α-axis of the unit cell showed a characteristic intramolecular classical O–H···O hydrogen bond between hydroxyl and carbonyl O atoms leading to self-associated (<i>Z</i>)-2-furanyl-acrylamides

One-Pot Tandem Approach to Functionalized 3‑Hydroxy-2-furanyl-acrylamides

A novel one-pot tandem process involving Knoevenagel condensation, Michael addition, selective amidation, and Paal–Knorr cyclization to diverse functionalized 3-hydroxy-2-furanyl-acrylamides from simple 2-oxoaldehydes and aroylacetonitriles was presented. Attempts were also made to expand the scope of the reaction to different 2-heteroarylfurans. The packing diagram of the molecules viewed down along the α-axis of the unit cell showed a characteristic intramolecular classical O–H···O hydrogen bond between hydroxyl and carbonyl O atoms leading to self-associated (<i>Z</i>)-2-furanyl-acrylamides

One-Pot Tandem Approach to Functionalized 3‑Hydroxy-2-furanyl-acrylamides

A novel one-pot tandem process involving Knoevenagel condensation, Michael addition, selective amidation, and Paal–Knorr cyclization to diverse functionalized 3-hydroxy-2-furanyl-acrylamides from simple 2-oxoaldehydes and aroylacetonitriles was presented. Attempts were also made to expand the scope of the reaction to different 2-heteroarylfurans. The packing diagram of the molecules viewed down along the α-axis of the unit cell showed a characteristic intramolecular classical O–H···O hydrogen bond between hydroxyl and carbonyl O atoms leading to self-associated (<i>Z</i>)-2-furanyl-acrylamides

Amino Catalytic Oxidative Thioesterification Approach to α‑Ketothioesters

An efficient metal-free method for the synthesis of α-ketothioesters is described for the first time. This reaction features the ability of pyrrolidine to fine-tune the reaction between 2-oxoaldehyde and thiols through iminium to the desired product in moderate to good yields. As an advantage, no external oxidants or metal catalysts are required in our method. Reactions performed under modified conditions lead to an apparent balance in reactivity of secondary amine and thiols toward 2-oxoaldehydes

A novel quinazolinone derivative induces cytochrome c interdependent apoptosis and autophagy in human leukemia MOLT-4 cells

Crosstalk between apoptosis and autophagy is budding as one of the novel strategies in the cancer therapeutics. The present study tinted toward the interdependence of autophagy and apoptosis induce by a novel quinazolinone derivative 2,3-dihydro-2-(quinoline-5-yl) quinazolin-4(1H)-one structure [DQQ] in human leukemia MOLT-4 cells. DQQ induces cytochrome c arbitrated apoptosis and autophagy in MOLT-4 cells. Apoptosis induces by DQQ was confirmed through a battery of assay e.g. cellular and nuclear microscopy, annexin-V assay, cell cycle analysis, loss of mitochondrial membrane potential and immune-expression of cytochrome c, caspases and PARP. Furthermore, acridine orange staining, LC3 immunofluorescence and western blotting of key autophagy proteins revealed the autophagic potential of DQQ. A universal caspase inhibitor, Z-VAD-FMK and cytochrome c silencing, strongly inhibited the DQQ induce autophagy and apoptosis. Beclin1 silencing through siRNA partially reversed the cell death, which was not as significant as by cytochrome c silencing. Although, it partially reversed the PARP cleavage induced by DQQ, indicating the role of autophagy in the regulation of apoptosis. The present study first time portrays the negative feedback potential of cytochrome c regulated autophagy and the importance of quinazolinone derivative in discovery of novel anticancer therapeutics

Metal-Free Oxidative Amidation of 2‑Oxoaldehydes: A Facile Access to α‑Ketoamides

A novel and efficient method for the synthesis of α-ketoamides, employing a dimethyl sulfoxide (DMSO)-promoted oxidative amidation reaction between 2-oxoaldehydes and amines under metal-free conditions is presented. Furthermore, mechanistic studies supported an iminium ion-based intermediate as a central feature of reaction wherein C₁-oxygen atom of α-ketoamides is finally derived from DMSO