Computation-guided scaffold exploration of 2E,6E-1,10-trans/cis-eunicellanes.

Eunicellane diterpenoids are a unique family of natural products containing a foundational 6/10-bicyclic framework and can be divided into two main classes, cis and trans, based on the configurations of their ring fusion at C1 and C10. Previous studies on two bacterial diterpene synthases, Bnd4 and AlbS, revealed that these enzymes form cis- and trans-eunicellane skeletons, respectively. Although the structures of these diterpenes only differed in their configuration at a single position, C1, they displayed distinct chemical and thermal reactivities. Here, we used a combination of quantum chemical calculations and chemical transformations to probe their intrinsic properties, which result in protonation-initiated cyclization, Cope rearrangement, and atropisomerism. Finally, we exploited the reactivity of the trans-eunicellane skeleton to generate a series of 6/6/6 gersemiane-type diterpenes via electrophilic cyclization.

Computational Evidence of the Incipient Oxocarbenium Ion as a "Hidden Intermediate" During the Cyclization of Hydroxyenol Ether into Spiroketal Under Mild Acidic Condition.

The synthesis of spiroketals has gained attention because of their importance in chemical and biological reactions. Yet, the mechanistic investigation of mild acid-catalyzed spiroketalization remains elusive and less explored in the literature and speculated that such transformations may proceed through the oxocarbenium ion intermediate; however, the existence of such species in mild acid-catalyzed spiroketalization is not documented. The computational study has been performed at M06-2X/6-31+G(d) level to examine the kinetically controlled product formation for such reactions and the intrinsic reaction coordinates of 1 d suggest that the reaction proceeds via a "one-step, two-stage" mechanism with the formation of transient oxocarbenium as a "hidden intermediate" in the reaction. This study reveals that stereoelectronic interactions devoid the formation of stable oxocarbenium ion intermediate after the proton transfer transition state in the mild acid catalyzed spiroketalization process.

Tandem Michael-anti-Michael Addition-Mediated Orthogonal Strapping of Diynones: Regioselective Spirocyclopentannulation of Oxindoles and Pyrazolones and DFT Validation.

An efficient protocol involving the transformation of sequentially generated recursive anions from heterocyclic precursors to orthogonally strap diynones through one pot transition-metal-free spirocyclopentannulation has been devised, employing oxindoles and pyrazolones as prototypical platforms. Insights into these regioselective tandem Michael-anti-Michael processes have been gleaned through DFT calculations.

Ultrasensitive colorimetric detection of fluoride and arsenate in water and mammalian cells using recyclable metal oxacalixarene probe: a lateral flow assay.

Globally 3 billion people are consuming water with moderately high concentrations of fluoride and arsenic. The development of a simple point of care (PoC) device or home device for the detection of fluoride/arsenic ensures safety before consuming water. Till date, lateral flow assay (LFA) based PoC devices can detect nucleic acids, viruses and diseases. An aluminium complex of rhodamine B functionalized oxacalix[4]arene (L) was designed to execute the LFA-based PoC device. Initially, Al3+ and Fe3+ ions were involved in complexation with the rhodamine B functionalized oxacalix[4]arene (L), resulting C1 (L-Al3+) and C2 (L-Fe3+) complexes respectively. The receptor L, as well as the probes (C1, C2), were characterized thoroughly using mass spectroscopy, FTIR, NMR, and EA. C1 and C2 were further utilized as recyclable probes for the detection of aqueous fluoride (21 ppb) and arsenate (1.92 ppb) respectively. The computational calculation indicates that upon complexation, the spirolactam ring opening at the rhodamine B site leads to optoelectronic changes. The consistency of LFA-based portable sensing device has been tested with water samples, synthetic fluoride standards and dental care products like toothpaste and mouthwash with concentrations ≥ 3 ppm. Moreover, fixed cell imaging experiments were performed to ascertain the in-vitro sensing phenomena.

Colorimetric dual sensor for Cu(II) and tyrosine and its application as paper strips for detection in water and human saliva as real samples.

A calix[4]arene based compound incorporating amide and morpholine moieties has been synthesized and its ion recognition property towards metal ions and application of its metal complex towards sensing of amino acids has been investigated. The synthesized compound interacts with Cu2+ with high selectivity and sensitivity (LOD, 0.1 ppb) in aqueous media with instant color change from colorless to yellow without interference from any other metal ions used in this study. The molecular structure of the calix compound (1) has been determined by single crystal X-ray study and the structure of its Cu2+ complex has been established by DFT calculation. The Cu2+ complex of 1 selectively detects tyrosine (LOD, 1.2 ppm) in water with distinct color change and without any interference from other 22 amino acids used in this study. The mechanism for detection of tyrosine with color change is also presented. For easy field application, paper based sensor strips have been prepared by coating compound 1 and its Cu2+ complex on filter paper, which have been used for semi-quantitative measurement of Cu2+ and tyrosine. Compound 1 and its Cu2+ complex have also been used for detection of Cu2+ and tyrosine, respectively in water and human saliva as real samples and satisfactory results are obtained.

Surfactant-Assisted Selective Oxidation of Aromatic Amines to Nitro Compounds by in Situ-Formed Performic Acid.

Development of novel and greener methods for the selective oxidation of various organic compounds is a challenging task. Herein, a novel protocol for the selective oxidation of aromatic amines to nitroaromatics at room temperature is developed. The oxidation reaction was carried out using a mixture of formic acid and aqueous hydrogen peroxide, which resulted in the in situ formation of performic acid. Further, improvement of selectivity was studied using different surfactants, of which cetyltrimethylammonium bromide (CTAB) gave the highest selectivity (85%) toward nitrobenzene. The role of CTAB in achieving higher selectivity is discussed. Under optimized reaction conditions, various substituted amines were successfully oxidized to corresponding nitro compounds. It is worth mentioning that this is the first report on oxidation of amines to nitro compounds in an aqueous medium with high selectivity.