Unlocking the potential of bile acids in synthesis, supramolecular/materials chemistry and nanoscience

The Maitra group has explored a variety of chemistry with bile acids during the past 15 years and these experiments have covered a wide variety of chemistry-asymmetric synthesis, molecular recognition, ion receptors/sensors, dendrimers, low molecular mass organo and hydrogelators, gel-nanoparticle composites, etc. Some of what excites us in this field is highlighted in this perspective article.     

Enantioselective synthesis of a potential key intermediate for the total synthesis of fumagillin

Key intermediate, 7, of a projected total synthesis of the anti-angiogenesis compound Fumagillin 1 and the semi-synthetic analogue TNP-470 2, has been prepared in enantiomerically pure form by employing an early nucleophilic addition ring closure [NARC] sequence to construct the cyclohexene backbone.     

Where the rubber meets the hand: Unlocking the sensing potential of dielectric elastomers

Practice makes perfect to some extent. Research has shown that musicians who practice the piano for long periods of time can suffer a range of hand problems from loss of control to diminished speed. Now imagine a rubber keyboard that is springy, soft, and elastic. This is the new type of input device that dielectric elastomers (DE) can create. However their usage in large sensing systems is limited by a scalability challenge. Each DE sensor is married to a pair of connection cables and electronics, adding to the complexity of the background overheads. A new efficient multi‐frequency method is presented that is capable of detecting internal pressure changes from a difference in the DE's capacitance without the need for any additional wires or connections. This effectively segments the DE into smaller sections, achieving information from a single sensor equivalent to multiple sensors. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 465–472     

Green chemical synthesis of fluorinated 1,3,5-triaryl-s-triazines in aqueous medium under microwaves as potential antifungal agents

Reasonable pure fluorinated s-triazines were synthesized in quantitative yield (96-99%) in 2-3 min in aqueous medium under microwaves, by reaction of fluorinated anilines and aqueous formaldehyde. All synthesized compounds have been screened in vitro for their antifungal activity against Rhizoctonia solani, Fusarium oxysporum, and Collectotrichum capsici.     

Molybdenum-catalyzed stannylations as key steps in heterocyclic synthesis

THF/carbonyl complexes of molybdenum and tungsten are suitable precursors for the synthesis of the corresponding monoisonitrile carbonyl complexes. Whereas complexes with electron-rich isonitriles are suitable for regioselective hydrostannations, complexes with electron-poor isonitriles are efficient catalysts for distannations, without reduction of aromatic halides. This allows for the synthesis of halogenated distannylated allyl ethers, which can be subjected to intramoleculare Stille couplings giving rise to heterocycles, which can be further modified at the remaining stannyl group.     

One-pot reductive-cyclization as key step for the synthesis of rutaecarpine alkaloids

The quinazolinocarboline alkaloids including rutaecarpine (1a), euxylophoricine A (1b), and euxylophoricine C (1c) have been synthesized efficiently from the ring opened β-carboline derivative as key intermediate by a one-pot reductive-cyclization reaction. The key intermediate was prepared from tryptamine (6) following Bischler-Napieralski cyclization, benzoylation, and oxidative cleavage of the exocyclic double bond.     

Novel synthesis of carbohydrates using electroreduction as key reactions

Glyceraldehyde was transformed to threose, erythrose, and erythrose using electro-reduction as key reactions.     

Photochemical reactions as key steps in five-membered N-heterocycle synthesis

The chemists have been interested in light as an energy source to induce chemical reactions since the beginning of scientific chemistry. This review summarizes the chemistry of photochemical reactions with emphasis of their synthetic applications. The organic photochemical reactions avoid the polluting or toxic reagents and therefore offer perspectives for sustainable processes and green chemistry. In summary, this review article describes the synthesis of a number of five-membered N-heterocycles.     

Photochemical reactions as key steps in natural product synthesis

Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.     

Radical-initiated cyclization as a key step for the synthesis of oxoprotoberberine alkaloids

The oxoprotoberberine alkaloids 1a-d have been synthesized efficiently from the enamide derivatives 2a-d by a radical-initiated cyclization reaction utilizing n-Bu₃SnH/AIBN and CuCl. The enamide derivatives 2a-d were prepared from phenylethylamine analogues 5a-b, followed by acylation with acetic anhydride, Bischler-Napieralski cyclization with POCl₃ and benzoylation with the corresponding bromobenzoyl chloride, respectively.     

Chiral imides as potential chiroptical switches: synthesis and optical properties

A series of chiral aromatic imides and diimides were synthesized and their electrochemical, absorption, fluorescent, and chiroptical properties were examined for their potential application as molecular chiroptical switches. These compounds exhibit strong UV-vis absorptions, and can be electrochemically reduced to radical anions that absorb in the near infrared (NIR) region. Further reduction to the dianionic states results in new absorptions in the visible region. The changes in circular dichroism upon redox switching were apparent in the UV-vis region but were absent in the NIR region.     

Comparative antibacterial potential of silver nanoparticles prepared via chemical and biological synthesis

New and improved approaches are urgently needed to fight the increasing number of multi-drug resistant bacteria. The antibacterial effect of silver nanoparticles (AgNPs) prepared by standardized chemical and biological syntheses is compered here. Biological systems included extracts of Opuntia ficus-indica mucilage and extracellular growth broth of Aspergillus niger and Bacillus megaterium. The nanoparticles were characterized by infrared spectroscopy, IR, and transmission electron microscopy. All of the AgNPs shared characteristic IR peaks and had an average size of 20–60 nm. The AgNPs were mainly spherical regardless of synthetic path. The synthesis based on the extracellular broth of the fungus, due to the highest biomass and active compounds concentration, resulted in a high yield of nanoparticle formation. These AgNPs also exhibited the highest inhibition zone against Salmonella typhimurium and Staphylococcus aureus. The syntheses reported here have no significant influence on AgNPs physical characteristics, as compared to literature, but represent processes with shorter reaction time. Additionally, the fungal based nanoparticles have superior antibacterial characteristics.     

Phosphide-borane complexes as key intermediates in the synthesis of optically active 1,3-oxaphospholanes

The syntheses, from the triphenylphosphine-borane complex, of chiral 1,3-oxaphospholanes and optically active bis-1,3-oxaphospholanes, obtained by cleavage of a carbon-phosphorus bond with lithium, are described. © 1997 John Wiley & Sons, Inc.     

Botcinolide/botcinin: asymmetric synthesis of the key fragments

The asymmetric synthesis of key fragments of the phytotoxic toxins botcinolide/botcinin is reported. The synthesis of 1 and 1a are based on a convergent route via esterification and alkene metathesis of fragments A, B or C, B, which were obtained by Evans aldol condensation and stereoselective crotylation, respectively.     

Unlocking the Potential of Bio-Based Nitrogen-Rich Furanic Platforms as Biomass Synthons

The demand for new biomass-derived fine and commodity chemicals propels the discovery of new methodologies and synthons. Whereas furfural and 5-hydroxymethylfurfural are cornerstones of sustainable chemistry, 3-acetamido-5-acetyl furan (3A5AF), an N-rich furan obtained from chitin biomass, remains unexplored, due to the poor reactivity of the acetyl group relative to previous furanic aldehydes. Here we developed a reactive 3-acetamido-5-furfuryl aldehyde (3A5F) and demonstrated the utility of this synthon as a source of bio-derived nitrogen-rich heteroaromatics, carbocycles, and as a bioconjugation reagent.     

Asymmetric synthesis of hydroxy-skipped bishomo-inositols as potential glycosidase inhibitors

Four isomeric hydroxy-skipped bishomo-inositol analogs have been synthesized from both enantiomers of 5-hydroxymethyl-2-cyclohexenone. Sharpless asymmetric dihydroxylation and substrate-directed anionic hydroxymethylation are the key reactions which have been employed successfully for the synthesis of new cyclitols. The synthesized cyclitols have been screened for their inhibitory effect on α- and β-glycosidases.     

The synthesis of malonimide derivatives as potential penicillin analogs

Malonimidoacetic acid derivatives (VIII, XIII) were synthesized as a potential penicillin analogs, hut they failed to inhibit the growth of bacteria when tested in vitro against a range of Gram-positive and Gram-negative microorganisms.     

Enantioselective synthesis of 5-methylidenedihydrouracils as potential anticancer agents

An efficient, versatile, enantioselective synthesis of 1,3-disubstituted and 1,3,6-trisubstituted 5-methylidenedihydrouracils applying Horner-Wadsworth Emmons methodology was developed. Starting 1,3-disubstituted 5-diethoxyphosphoryluracils were subjected to reduction of the double bond or addition of various Grignard reagents and obtained Horner-Wadsworth Emmons reagents were used for the olefination of formaldehyde. Enantioselective synthesis of 1,3,6-trisubstituted 5-methylidenedihydrouracils was accomplished by introducing (R,R)- or (S,S)-di(1-phenylethylamino)phosphoryl groups as chiral auxiliary. Additions of Grignard reagents in the presence of these groups were highly and complimentary diastereoselective (de?～?80%). Further separation of the diastereomeric mixtures by column chromatography enabled synthesis of (R)- and (S)-1,3,6-trisubstituted-5-methylidenedihydrouracils with ee?≥?98%. Furthermore, absolute configuration of the adducts and final products was established using single crystal X-ray analysis. Stereochemical course of the addition reactions is also discussed.