Microwave-Assisted Synthesis of Five-Membered O,N,N-Heterocycles

The development of new strategies for synthesis of five-membered O,N,N-heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in oxygen and two nitrogen atoms containing five-membered heterocyclic compounds synthesis is presented, focusing on the developments in the past 5–10 years. This contribution covers the literature concerning the total synthesis of five-membered O,N,N-heterocycles.     

Microwave-Assisted Synthesis of Six-Membered O-Heterocycles

The development of new strategies for synthesis of six-membered O-heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in oxygen-containing six-membered heterocyclic compounds synthesis is presented, focusing on the developments in the past 5–10 years. This contribution covers the literature concerning the total synthesis of six membered O-heterocycles.     

Nitrogen-Containing Six-Membered Heterocycles: Solid-Phase Synthesis

Solid-phase organic synthesis is a rapidly expanding area of synthetic chemistry that is being widely exploited in the search for new medicinally important compounds using combinatorial techniques. In recent decades, a large number of reports related to solid-phase synthesis of heterocycles have appeared because of the wide variety of their biological activity. In this review, we report the important role of solid-phase synthesis in the synthesis of nitrogen containing six-membered ring heterocycles.     

Poor quality drugs: grand challenges in high throughput detection, countrywide sampling, and forensics in developing countries

Throughout history, poor quality medicines have been a persistent problem, with periodical crises in the supply of antimicrobials, such as fake cinchona bark in the 1600s and fake quinine in the 1800s. Regrettably, this problem seems to have grown in the last decade, especially afflicting unsuspecting patients and those seeking medicines via on-line pharmacies. Here we discuss some of the challenges related to the fight against poor quality drugs, and counterfeits in particular, with an emphasis on the analytical tools available, their relative performance, and the necessary workflows needed for distinguishing between genuine, substandard, degraded and counterfeit medicines.     

Chemical modification of L-glutamine to alpha-amino glutarimide on autoclaving facilitates Agrobacterium infection of host and non-host plants: A new use of a known compound

Background

Accidental autoclaving of L-glutamine was found to facilitate the Agrobacterium infection of a non host plant like tea in an earlier study. In the present communication, we elucidate the structural changes in L-glutamine due to autoclaving and also confirm the role of heat transformed L-glutamine in Agrobacterium mediated genetic transformation of host/non host plants.

Results

When autoclaved at 121°C and 15 psi for 20 or 40 min, L-glutamine was structurally modified into 5-oxo proline and 3-amino glutarimide (α-amino glutarimide), respectively. Of the two autoclaved products, only α-amino glutarimide facilitated Agrobacterium infection of a number of resistant to susceptible plants. However, the compound did not have any vir gene inducing property.

Conclusions

We report a one pot autoclave process for the synthesis of 5-oxo proline and α-amino glutarimide from L-glutamine. Xenobiotic detoxifying property of α-amino glutarimide is also proposed.     

The synthesis of dehydrotryptophan and dehydrotryptophan-containing peptides

Dehydrotryptophan and its derivatives are non-proteinogenic amino acids commonly found in peptide-based natural products produced by microorganisms, marine organisms and plants. These non-proteinogenic amino acids are found in secondary metabolites and are formed by post translational modification processes. Although comprehensive reviews on the synthesis of dehydroamino acids are available, this perspective focuses solely on methods to synthesise the dehydrotryptophan-containing segment of naturally occurring peptides, amino acids and their derivatives.     

A new rapid multicomponent domino reaction for the formation of functionalized benzo[h]pyrazolo[3,4-b]quinolines

A new multicomponent domino reaction for rapid and regioselective synthesis of highly functionalized benzo[h]pyrazolo[3,4-b]quinolines has been established. The reaction can be conducted by using readily available and inexpensive substrates under microwave irradiation within short periods of 10-26 min. Good to excellent chemical yields (61-91%) and complete regioselectivity have been achieved for 22 examples. Tedious work-up procedure can be avoided due to the direct precipitation of products from the reaction solution. The resulting benzoquinolines have been readily converted into quinoxaline-fused benzo[h]isoxazolo[5,4-b]quinoline analogues by treating with benzene-1,2-diamine under microwave irradiation. The structural assignment has been ambiguously confirmed by X-ray analysis. A new mechanism has been proposed for this new multicomponent domino process.     

Dansyl-anthracene dyads for ratiometric fluorescence recognition of Cu2+

Dansyl-anthracene dyads 1 and 2 in CH(3)CN-H(2)O (7:3) selectively recognize Cu(2+) ions amongst alkali, alkaline earth and other heavy metal ions using both absorbance and fluorescence spectroscopy. In absorbance, the addition of Cu(2+) to the solution of dyads 1 or 2 results in appearance of broad absorption band from 200 nm to 725 nm for dyad 1 and from 200 nm to 520 nm for dyad 2. This is associated with color change from colorless to blue (for 1) and fluorescent green (for 2). This bathochromic shift of the spectrum could be assigned to internal charge transfer from sulfonamide nitrogen to anthracene moiety. In fluorescence, under similar conditions dyads 1 and 2 on addition of Cu(2+) selectively quench fluorescence due to dansyl moiety between 520-570 nm (for 1)/555-650 nm (for 2) with simultaneous fluorescence enhancement at 470 nm and 505 nm for dyads 1 and 2, respectively. Hence these dyads provide opportunity for ratiometric analysis of 1-50 μM Cu(2+). The other metal ions viz. Fe(3+), Co(2+), Ni(2+), Cd(2+), Zn(2+), Hg(2+), Ag(+), Pb(2+), Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ba(2+) do not interfere in the estimation of Cu(2+) except Cr(3+) in case of dyad 1. The coordination of dimethylamino group of dansyl unit with Cu(2+) causes quenching of fluorescence due to dansyl moiety between 520-600 nm and also restricts the photoinduced electron transfer from dimethylamino to anthracene moiety to release fluorescence between 450-510 nm. This simultaneous quenching and release of fluorescence respectively due to dansyl and anthracene moieties emulates into Cu(2+) induced ratiometric change.     

CN- scavenger: a leap towards development of a CN- antidote

Compound 4 removes cyanide from water and human serum in the form of compound 7 (cyano-derivative of 4) and experiments show its suitability as an antidote of CN(-) poisoning.