Prebiotic synthesis of α-amino acids and orotate from α-ketoacids potentiates transition to extant metabolic pathways.

The Strecker reaction of aldehydes is the pre-eminent pathway to explain the prebiotic origins of α-amino acids. However, biology employs transamination of α-ketoacids to synthesize amino acids which are then transformed to nucleobases, implying an evolutionary switch-abiotically or biotically-of a prebiotic pathway involving the Strecker reaction into today's biosynthetic pathways. Here we show that α-ketoacids react with cyanide and ammonia sources to form the corresponding α-amino acids through the Bucherer-Bergs pathway. An efficient prebiotic transformation of oxaloacetate to aspartate via N-carbamoyl aspartate enables the simultaneous formation of dihydroorotate, paralleling the biochemical synthesis of orotate as the precursor to pyrimidine nucleobases. Glyoxylate forms both glycine and orotate and reacts with malonate and urea to form aspartate and dihydroorotate. These results, along with the previously demonstrated protometabolic analogues of the Krebs cycle, suggest that there can be a natural emergence of congruent forerunners of biological pathways with the potential for seamless transition from prebiotic chemistry to modern metabolism.

Cyanide as a primordial reductant enables a protometabolic reductive glyoxylate pathway.

Investigation of prebiotic metabolic pathways is predominantly based on abiotically replicating the reductive citric acid cycle. While attractive from a parsimony point of view, attempts using metal/mineral-mediated reductions have produced complex mixtures with inefficient and uncontrolled reactions. Here we show that cyanide acts as a mild and efficient reducing agent mediating abiotic transformations of tricarboxylic acid intermediates and derivatives. The hydrolysis of the cyanide adducts followed by their decarboxylation enables the reduction of oxaloacetate to malate and of fumarate to succinate, whereas pyruvate and α-ketoglutarate themselves are not reduced. In the presence of glyoxylate, malonate and malononitrile, alternative pathways emerge that bypass the challenging reductive carboxylation steps to produce metabolic intermediates and compounds found in meteorites. These results suggest a simpler prebiotic forerunner of today's metabolism, involving a reductive glyoxylate pathway without oxaloacetate and α-ketoglutarate-implying that the extant metabolic reductive carboxylation chemistries are an evolutionary invention mediated by complex metalloproteins.

A Plausible Prebiotic One-Pot Synthesis of Orotate and Pyruvate Suggestive of Common Protometabolic Pathways.

A reaction between two prebiotically plausible building blocks, hydantoin and glyoxylate, generates both the nucleobase orotate, a precursor of biological pyrimidines, and pyruvate, a core metabolite in the citric acid cycle and amino acid biosynthesis. The reaction proceeds in water to provide significant yields of the two widely divergent chemical motifs. Additionally, the reaction of thiohydantoin and glyoxylate produces thioorotate in high yield under neutral aqueous conditions. The use of an open-chain thiohydantoin derivative also enables the potential pre-positioning of a nucleosidic bond prior to the synthesis of an orotate nucleoside. The observation that diverse building blocks of modern metabolism can be produced in a single reaction pot, from common reactants under mild conditions, supports the plausibility of orthogonal chemistries operating at the origins of chemical evolution.

A plausible metal-free ancestral analogue of the Krebs cycle composed entirely of α-ketoacids.

Efforts to decipher the prebiotic roots of metabolic pathways have focused on recapitulating modern biological transformations, with metals typically serving in place of cofactors and enzymes. Here we show that the reaction of glyoxylate with pyruvate under mild aqueous conditions produces a series of α-ketoacid analogues of the reductive citric acid cycle without the need for metals or enzyme catalysts. The transformations proceed in the same sequence as the reverse Krebs cycle, resembling a protometabolic pathway, with glyoxylate acting as both the carbon source and reducing agent. Furthermore, the α-ketoacid analogues provide a natural route for the synthesis of amino acids by transamination with glycine, paralleling the extant metabolic mechanisms and obviating the need for metal-catalysed abiotic reductive aminations. This emerging sequence of prebiotic reactions could have set the stage for the advent of increasingly sophisticated pathways operating under catalytic control.

Chemistry of Abiotic Nucleotide Synthesis.

The chemistry of abiotic nucleotide synthesis of RNA and DNA in the context of their prebiotic origins on early earth is a continuing challenge. How did (or how can) the nucleotides form and assemble from the small molecule inventories and under conditions that prevailed on early earth 3.5-4 billion years ago? This review provides a background and up-to-date progress that will allow the reader to judge where the field stands currently and what remains to be achieved. We start with a brief primer on the biological synthesis of nucleotides, followed by an extensive focus on the prebiotic formation of the components of nucleotides-either via the synthesis of ribose and the canonical nucleobases and then joining them together or by building both the conjoined sugar and nucleobase, part-by-part-toward the ultimate goal of forming RNA and DNA by polymerization. The review will emphasize that there are-and will continue to be-many more questions than answers from the synthetic, mechanistic, and analytical perspectives. We wrap up the review with a cautionary note in this context about coming to conclusions as to whether the problem of chemistry of prebiotic nucleotide synthesis has been solved.

Bis(dimethylamino)phosphorodiamidate: A Reagent for the Regioselective Cyclophosphorylation of cis-Diols Enabling One-Step Access to High-Value Target Cyclophosphates.

Bis(dimethylamino)phosphorodiamidate (BDMDAP) enables an efficient and one-pot cyclophosphorylation of vicinal cis-diol moiety of polyol-organics of biological importance without the need for protecting group chemistry and is amenable to large-scale reactions. The utility of this reagent is demonstrated through the synthesis of high-value targets such as cyclic phosphates of myo-inositol, nucleosides, metabolites, and drug molecules.

Effect of temperature modulations on TEMPO-mediated regioselective oxidation of unprotected carbohydrates and nucleosides.

Regioselective oxidation of unprotected and partially protected oligosaccharides is a much sought-after goal. Herein, we report a notable improvement in the efficiency of TEMPO-catalyzed oxidation by modulating the temperature of the reaction. Mono-, di-, and tri-saccharides are oxidized regioselectively in yields of 75 to 92%. The present method is simple to implement and is also applicable for selective oxidations of other mono- and poly-hydroxy compounds including unprotected and partially protected nucleosides.

Rapid resolution of carbohydrate isomers via multi-site derivatization ion mobility-mass spectrometry.

Identifying small sugar isomers can be challenging by ion mobility-mass spectrometry (IM-MS) alone due to their small collision cross section differences. Herein, we report IM-MS results for multi-site, covalent carbohydrate derivatization with 3-carboxy-5-nitrophenylboronic acid (3C5NBA). Following reaction in aqueous solutions at room temperature, 3C5NBA reacts with each mono- or disaccharide molecule to yield products that each have a distinguishable mobility signature. The reaction was rapid and resulted in the detection of products within 5 min after 3C5NBA was mixed with the analyte. Eight disaccharides that varied in linkage, composition, and configuration (α or ß) as well as four monosaccharides, d-glucose, d-galactose, d-mannose and d-fructose, were included in this study. The derivatives' drift times showed significant shifts, with up to 3-fold gains in resolution when compared to previous literature reports. Moreover, the specific MS/MS fragmentation information gathered from these sugar derivatives provided further validation of the isomers' structures.

Synthesis and immunopotentiating activity of novel isoxazoline functionalized coumarins.

A novel series (13) of isoxazoline functionalized coumarins was synthesized through 1,3-dipolar cyclization of nitrile oxides with Allylated coumarins. Synthesis of effective and target selective immunostimulators through conjugation of diversely substituted isoxazolines and 7-hydroxycoumarins is the focus of the present article. The proposed synthetic scheme was observed to be highly regiospecific yielding attempted conjugates in good yield (>90%). Kinetic resolution of the racemates was carried out by employing lipase B from Candida antarctica (CALB). The synthesized compounds were screened in vitro and in vivo for their biological activities viz. toxicity and impact on splenocyte proliferation (T- and B-cell proliferation), antibody production (HA titre), delayed-type hypersensitivity reaction (DTH), T-cell subtypes (CD4 and CD8), cytokine production (IL-2, IFN-γ, and IL-4) and NO (macrophage) production. Our results establish that isoxazoline functionalized coumarins exhibit excellent immune potentiating activity especially compounds 2, 4 and 8 whose activity is more than that of Levimasole as standard. The structure activity relations are explained in light of the structural/functional aspects of tested compounds. To the best of our knowledge the presented work is first of its kind and is presaged to prove very useful for the design and synthesis of bis-heterocycle based novel, therapeutically selective and effective immunopotentiators.

Metal-Free, Phosphonium Salt-Mediated Sulfoximination of Azine N-Oxides: Approach for the Synthesis of N-Azine Sulfoximines.

Herein, we report a simple and metal-free method for the synthesis of N-azine sulfoximines by the nucleophilic substitution of azine N-oxides with NH-sulfoximines. The present method works at room temperature with wide functional group compatibility and gives several unprecedented N-azine sulfoximines. The reaction conditions were also found suitable with enantiopure substrates and furnished products without any racemization. It also finds an application in the sulfoximination of azine-based functional molecules such as 2,2'-bipyridine, 1,10-phenanthroline, and quinine.

Metal-Free Approach for the Synthesis of N-Aryl Sulfoximines via Aryne Intermediate.

A metal-free and operationally simple N-arylation of NH-sulfoximines with aryne precursors is reported. Transition metal-free reaction conditions and shorter reaction times are the highlights of the present method. The mild optimized condition was also found to be suitable with enantiopure substrates.

Dimethyltin Dichloride Catalyzed Regioselective Alkylation of cis-1,2-Diols at Room Temperature.

Here, we have developed a mild and general method for the regioselective installation of benzyl, allyl, para-methoxybenzyl and naphthyl groups on cis-1,2-diols. The optimized method operates at room temperature using dimethyltin dichloride as catalyst and silver oxide as an additive. The present method works well with both sugars (such as mono- and disaccharides) and nonsugars (such as inositols, propan-1,2-diol, 1,2-cycloalkanediols and anhydroerythritol) and also provides comparatively better functional group compatibility.

Transbilayer lipid interactions mediate nanoclustering of lipid-anchored proteins.

Understanding how functional lipid domains in live cell membranes are generated has posed a challenge. Here, we show that transbilayer interactions are necessary for the generation of cholesterol-dependent nanoclusters of GPI-anchored proteins mediated by membrane-adjacent dynamic actin filaments. We find that long saturated acyl-chains are required for forming GPI-anchor nanoclusters. Simultaneously, at the inner leaflet, long acyl-chain-containing phosphatidylserine (PS) is necessary for transbilayer coupling. All-atom molecular dynamics simulations of asymmetric multicomponent-membrane bilayers in a mixed phase provide evidence that immobilization of long saturated acyl-chain lipids at either leaflet stabilizes cholesterol-dependent transbilayer interactions forming local domains with characteristics similar to a liquid-ordered (lo) phase. This is verified by experiments wherein immobilization of long acyl-chain lipids at one leaflet effects transbilayer interactions of corresponding lipids at the opposite leaflet. This suggests a general mechanism for the generation and stabilization of nanoscale cholesterol-dependent and actin-mediated lipid clusters in live cell membranes.

HClO4-silica-catalysed regioselective opening of benzylidene acetals and its application towards regioselective HO-4 glycosylation of benzylidene acetals in one-pot.

Here we report a high-yielding method for the regioselective reductive ring opening of 4,6-O-benzylidene acetals of hexapyranosides using inexpensive and robust HClO4-SiO2 as the acidic catalyst and triethylsilane as the hydride donor. Under the optimized condition, gluco- and mannopyranosides give the respective 6-O-benzyl derivative in good to excellent yields while the corresponding galactopyranoside gives the corresponding 6-O-benzyl derivative in lower yield. As the optimized condition involves acidic catalyst, we also successfully developed further application of the present method for the tandem regioselective opening and glycosylation in one-pot.

Synthesis of non-hydrolysable mimics of glycosylphosphatidylinositol (GPI) anchors.

Synthesis of first generation non-hydrolysable C-phosphonate GPI analogs, viz., 6-O-(2-amino-2-deoxy-α-d-glucopyranosyl)-d-myo-inositol-1-O-(sn-3,4-bis(palmitoyloxy)butyl-1-phosphonate) and 6-O-(2-amino-2-deoxy-α-d-glucopyranosyl)-d-myo-inositol-1-O-(sn-2,3-bis(palmitoyloxy)propyl-1-phosphonate) 23b, is reported. The target compounds were synthesized by the coupling of α-pseudodisaccharide 21 with phosphonic acids 18a and 18b respectively in quantitative yield followed by de-protection. These synthetic C-phosphonate GPI-probes were resistant to phosphatidylinositol specific phospholipase C (PI-PLC) and also showed moderate inhibition of the enzyme activity.

Iron-catalyzed cross-coupling of electron-deficient heterocycles and quinone with organoboron species via innate C-H functionalization: application in total synthesis of pyrazine alkaloid botryllazine A.

Here, we report an iron-catalyzed cross-coupling reaction of electron-deficient heterocycles and quinone with organoboron species via innate C-H functionalization. Iron(II) acetylacetonate along with oxidant (K2S2O8) and phase-transfer catalyst (TBAB) under open flask conditions efficiently catalyzed the cross-coupling of pyrazine with arylboronic acids and gave monoarylated products in good to excellent yields. Optimized conditions also worked for other heterocylces such as quinoxalines, pyridines, quinoline, and isoquinoline as well as quinones. In addition, we demonstrated as a first example its application for the synthesis of anticancer marine pyrazine alkaloid botryllazine A.

New method for C-H arylation/alkylation at α-position of cyclic aliphatic ethers by iron-oxide mediated reaction.

We report a new and efficient iron oxide catalyzed cross-coupling reaction between organometallic species such as alkyl/arylmagnesium halides or organolithium species and α-hydrogen bearing cyclic unbranched and branched aliphatic ethers via activation of C(sp(3))-H. In the presence of 1 mol% of iron oxide, five and six membered unbranched cyclic ethers such as tetrahydrofuran and tetrahydropyran gave good to excellent yields of cross-coupled products. Whereas, in case of branched ether such as 2-methyltetrahydrofuran, it was observed that the arylation occurred at both the sides and gave moderate yields of a mixture of regioisomers. Among the organometallic species used, alkyl organometallic reagents gave less yields as compared to aryl organometallics.