1,1-Diaminoazines as organocatalysts in phospha-Michael addition reactions.

1,1-Diaminoazines can act as effective organocatalysts for the formation of phosphorus-carbon bonds between biphenylphosphine oxide and an activated alkene (Michael acceptor). These catalysts provide the P-C adducts at a faster rate and with relatively better yields in comparison to the organocatalysts employed earlier. The notable advantage is that 1,1-diaminoazines catalyse the reaction even in an aqueous medium with very good yields. Organocatalysis using 1,1-diaminoazines was also successfully carried out between dimethylphosphite and benzylidenemalononitrile under multicomponent conditions.

Iodine Catalyzed Oxidative Coupling of Diaminoazines and Amines for the Synthesis of 3,5-Disubstituted-1,2,4-Triazoles.

A simple, convenient, transition metal-free one pot synthesis of 3,5-disubstituted-1,2,4-triazoles has been established. The innovation in this reaction is the use of easily available 1,1-diaminoazines as substrates. This method provides the products with wider substrate scope, at an expedited rate, and with relatively better yields in comparison to the reported methods. The reaction mechanism involves an initial intermolecular nucleophilic addition (facilitated by I2) followed by intramolecular nucleophilic cyclization.

Azines: synthesis, structure, electronic structure and their applications.

Azines are organic molecules which bear the C[double bond, length as m-dash]N-N[double bond, length as m-dash]C functional unit. In the recent past, azines have received increased attention due to the recognition of their biological, chemical and materials properties. Azines have been conventionally synthesised by the condensation of hydrazine with ketones and aldehydes, and many alternate routes are also available. Azines have been extensively studied to investigate the presence or absence of conjugation with the help of computational studies and crystal structure analysis owing to their importance in nonlinear optics. The tautomerism in azines is a topic of contemporary interest. Herein, we present a review of recent advances in the structure and electronic structure properties of azines along with information on the modern methods of their synthesis and application as precursors in generating heterocycles in organic synthesis and in medicinal chemistry. A few applications of azines in the field of materials chemistry in developing metal-organic frameworks (MOFs), covalent organic frameworks (COFs), energetic materials and chemosensors are also included.

An unprecedented intramolecular to intermolecular mechanistic switch in 1,1-diaminoazines leading to differential product formation during the I2-induced tandem oxidative transformation.

The tautomeric preference of guanylhydrazones towards the azine form induces an unprecedented intramolecular to intermolecular mechanistic switch during the I2-catalyzed oxidative transformation leading to 4,5-disubstituted-3-amino-1,2,4-triazoles in contrast to the reaction of semicarbazones and thiosemicarbazones to form 1,3,4-oxa/thiadiazoles. This intramolecular to intermolecular cyclization shift was established through control experiments and was attributed to the high energy demand (∼22 kcal mol-1) for the azine tautomer to adopt the s-cis conformation which is essential for the intramolecular reaction. An I2 induced protocol for an efficient and straightforward synthesis of 4,5-disubstituted-3-amino-1,2,4-triazoles has been developed via tandem oxidative transformation of guanylhydrazones (in its preferentially existing azine tautomeric form) with distinct advantages such as wide substrate scope, use of substoichiometric amounts of iodine, no requirement of external oxidizing agents, base free reaction conditions, short reaction time and moderate to good yields. The role of silver salt in improving the yield and shortening of reaction time was also highlighted.

Rationalization of Benzazole-2-carboxylate versus Benzazine-3-one/Benzazine-2,3-dione Selectivity Switch during Cyclocondensation of 2-Aminothiophenols/Phenols/Anilines with 1,2-Biselectrophiles in Aqueous Medium.

The cyclocondensation reaction of 2-aminothiophenols with 1,2-biselectrophiles such as ethyl glyoxalate and diethyl oxalate in aqueous medium leads to the formation of benzothiazole-2-carboxylates via the 5-endo-trig process contrary to Baldwin's rule. On the other hand, the reaction of 2-aminophenols/anilines produced the corresponding benzazine-3-ones or benzazine-2,3-diones via the 6-exo-trig process in compliance with Baldwin's rule. The mechanistic insights of these cyclocondensation reactions using the hard-soft acid-base principle, quantum chemical calculations (density functional theory), and orbital interaction studies rationalize the selectivity switch of benzothiazole-2-carboxylates versus benzazine-3-ones/benzazine-2,3-diones. The presence of water facilitates these cyclocondensation reactions by lowering of the energy barrier.

Azine-Hydrazone Tautomerism of Guanylhydrazones: Evidence for the Preference Toward the Azine Tautomer.

Guanylhydrazones have been known for a long time and have wide applications in organic synthesis, medicinal chemistry, and material science; however, little attention has been paid toward their electronic and structural properties. Quantum chemical analysis on several therapeutically important guanylhydrazones indicated that all of them prefer the azine tautomeric state (by about 3-12 kcal/mol). A set of simple and conjugated azines were designed using quantum chemical methods, whose tautomeric preference toward the azine tautomer is in the range of 3-8 kcal/mol. Twenty new azines were synthesized and isolated in their neutral state. Variable temperature NMR study suggests existence of the azine tautomer even at higher temperatures with no traces of the hydrazone tautomer. The crystal structures of two representative compounds confirmed that the title compounds prefer to exist in their azine tautomeric form.

Design and synthesis of pyrazole-oxindole conjugates targeting tubulin polymerization as new anticancer agents.

A series of twenty one compounds with pyrazole and oxindole conjugates were synthesized by Knoevenagel condensation and investigated for their antiproliferative activity on different human cancer cell lines. The conjugates are comprised of a four ring scaffold; the structural isomers 12b and 12c possess chloro-substitution in the D ring. Among the congeners 12b, 12c, and 12d manifested significant cytotoxicity and inhibited tubulin assembly. Treatments with 12b, 12c and 12d resulted in accumulation of cells in G2/M phase, disruption of microtubule network, and increase in cyclin B1 protein. Zebrafish screening revealed that 12b, and 12d caused developmental defects. Docking analysis demonstrated that the congeners occupy the colchicine binding pocket of tubulin.

Synthesis and biological evaluation of imidazopyridine-oxindole conjugates as microtubule-targeting agents.

A library of imidazopyridine-oxindole conjugates was synthesised and investigated for anticancer activity against various human cancer cell lines. Some of the tested compounds, such as 10 a, 10 e, 10 f, and 10 k, exhibited promising antiproliferative activity with GI50 values ranging from 0.17 to 9.31 µM. Flow cytometric analysis showed that MCF-7 cells treated by these compounds arrested in the G2 /M phase of the cell cycle in a concentration-dependent manner. More particularly, compound 10 f displayed a remarkable inhibitory effect on tubulin polymerisation. All the compounds depolarised mitochondrial membrane potential and caused apoptosis. These results are further supported by the decreased phosphorylation of Akt at Ser473. Studies on embryonic development revealed that the lead compounds 10 f and 10 k caused delay in the development of zebra fish embryos. Docking of compound 10 f with tubulin protein suggested that the imidazo[1,2-a]pyridine moiety occupies the colchicine binding site of tubulin.

Isolation, synthesis and biological evaluation of phenylpropanoids from the rhizomes of Alpania galanga.

Bioactivity guided investigation of the DCM: MeOH (1:1) extract from the rhizomes of Alpinia galanga led to the isolation of phenylpropanoids (1-9) and their structures were established by 1H NMR, 13C NMR, IR a nd LC-MS/MS. Th ese compounds have b een evaluated for their in vitro anticanceractivity against the human cancer cell lines A549 (lung cancer), Colo-205 (colon cancer), A431 (skin cancer), NCI H460 (lung cancer), PC-3 (prostate cancer), and HT-29 (colon cancer). Compounds 4 and 9 showed potent anticancer activity (ranging from 1.3-19.7 microg/mL) against all the tested cancer cell lines. In addition, an asymmetric synthesis of acetoxychavicol acetate (1) and trans-p-coumaryl alcohol (4) has been accomplished in six steps starting from readily available p-hydroxybenzaldehyde for the first time. Grignard reaction and Sharpless kinetic resolution reactions were utilized as the key steps to install the basic core.