Physio-biochemical and molecular stress regulators and their crosstalk for low-temperature stress responses in fruit crops: A review.

Low-temperature stress (LTS) drastically affects vegetative and reproductive growth in fruit crops leading to a gross reduction in the yield and loss in product quality. Among the fruit crops, temperate fruits, during the period of evolution, have developed the mechanism of tolerance, i.e., adaptive capability to chilling and freezing when exposed to LTS. However, tropical and sub-tropical fruit crops are most vulnerable to LTS. As a result, fruit crops respond to LTS by inducing the expression of LTS related genes, which is for climatic acclimatization. The activation of the stress-responsive gene leads to changes in physiological and biochemical mechanisms such as photosynthesis, chlorophyll biosynthesis, respiration, membrane composition changes, alteration in protein synthesis, increased antioxidant activity, altered levels of metabolites, and signaling pathways that enhance their tolerance/resistance and alleviate the damage caused due to LTS and chilling injury. The gene induction mechanism has been investigated extensively in the model crop Arabidopsis and several winter kinds of cereal. The ICE1 (inducer of C-repeat binding factor expression 1) and the CBF (C-repeat binding factor) transcriptional cascade are involved in transcriptional control. The functions of various CBFs and aquaporin genes were well studied in crop plants and their role in multiple stresses including cold stresses is deciphered. In addition, tissue nutrients and plant growth regulators like ABA, ethylene, jasmonic acid etc., also play a significant role in alleviating the LTS and chilling injury in fruit crops. However, these physiological, biochemical and molecular understanding of LTS tolerance/resistance are restricted to few of the temperate and tropical fruit crops. Therefore, a better understanding of cold tolerance's underlying physio-biochemical and molecular components in fruit crops is required under open and simulated LTS. The understanding of LTS tolerance/resistance mechanism will lay the foundation for tailoring the novel fruit genotypes for successful crop production under erratic weather conditions.

Copper-catalyzed cascade reaction of tryptamines with diazo compounds to access hexahydropyrroloindoline derivatives.

A domino reaction sequence of cyclopropanation/ring-opening/iminium cyclization of tryptamine derivatives with donor-acceptor diazo compounds is developed to furnish pyrroloindolines, creating three consecutive stereogenic centers in a single step. The copper-catalyzed reaction provides pyrroloindolines at room-temperature with good substrate scope.

Palladium-Catalyzed C(sp3)-H Biarylation of 8-Methyl Quinolines with Cyclic Diaryliodonium Salts to Access Functionalized Biaryls and Fluorene Derivatives.

Herein, we have developed the cyclic diaryliodonium salts as biarylating agents in the C(sp3)-H functionalization using 8-methyl quinoline as the intrinsic directing group. The oxidant-free reaction produces a vast array of the biarylated products with iodo functionality that can be further functionalized. Additionally, intramolecular C(sp3)-H functionalization in a stepwise manner under palladium-catalyzed conditions produced the fluorene derivatives in excellent yields.

Regiodivergent cascade cyclization/alkoxylation of allenamides via N-protecting group driven rearrangement to access indole and indoline derivatives.

A mild, palladium-catalyzed domino Heck-cyclization/alkoxylation sequence of aryl halide tethered allenamides is described, providing regiodivergent indole and indoline derivatives controlled by the N-protecting group. This room temperature reaction provided a functionalizable olefinic moiety with broad substrate scope. Preliminary mechanistic studies support the rearrangement of an indoline-derived intermediate to indoles with the N-acetyl allenamides forming free (NH) indoles.

Transfer hydrogenation of pyridinium and quinolinium species using ethanol as a hydrogen source to access saturated N-heterocycles.

Catalytic transfer hydrogenation (TH) for the reduction of heterocycles is an emerging strategy for accessing biologically active saturated N-heterocycles. Herein, we report a TH protocol that utilizes ethanol as a renewable hydrogen source and an Ir catalyst for the reduction of quinolines and pyridines. The reaction is promoted by simple amides as ligands.

Dicarbofunctionalization of unactivated alkenes by palladium-catalyzed domino Heck/intermolecular direct hetero arylation with heteroarenes.

A palladium-catalyzed domino Heck/intermolecular direct hetero arylation sequence of unactivated alkenes was developed, providing 1,2,3-triazole containing bisheterocycles bearing all-carbon quaternary centers with yields of 25-90%. The protocol was extended to 1,3,4-oxadiazoles as well. The installed triazole was further exploited for late-stage functionalizations, and the mechanistic studies indicate the involvement of C-H activation.