Seven-membered N-heterocycles: metal and nonmetal assisted synthesis

The investigation of facial synthetic methods for chemical synthesis is a growing area of interest due to increasing environmental issues. The use of catalysts in organic reactions has gained extensive interest. Metal and nonmetal catalysts provided a new improved alternative to traditional methods in modern synthetic chemistry. The aim of the present review is to focus on the applications of metals and nonmetals for the synthesis of seven-membered N-heterocycles.     

A chiron approach to aminocytitols by petasis-borono-mannich reaction: formal synthesis of (+)-conduramine e and (-)-conduramine e

A chiron approach to a stereoselective route for the synthesis of aminocytitols from carbohydrates is described. The formal synthesis of (+)-conduramine E and (-)-conduramine E was achieved by utilizing this strategy. The key features of the synthetic strategy include one-pot three-component Petasis-Borono-Mannich reaction to introduce the syn-β-amino alcohol functionality of conduramine E and ring-closing metathesis to construct its carbocyclic core. The present synthetic approach paves the way for stereoselective synthesis of several conduramines starting from carbohydrates.     

Ultrasound-assisted green one-pot synthesis of linked bis-heterocycle peptidomimetics via IMCR/post-transformation/tandem strategy

The sequential aligning of two eco-friendly and powerful tools for the synthesis of peptidomimetics resulted in the rapid generation of molecular complexity in target molecules. We herein report a versatile IMCR/post-transformation/tandem synthetic strategy that emphasizes the special role of orthogonal bifunctional reagents in isocyanide based multicomponent reactions (IMCR) to generate a synthetic platform for subsequent heterocyclization reactions. This is the first one-pot synthesis of a 2,5-diketopiperazine linked to a 1,4-disubstituted 1,2,3-triazole. The Ugi-4CR/lactamization/click sequence is facile, mild, atom-economical, and green. The present work contributes to the green and one-pot synthesis of bis-heterocycle peptidomimetics and design of new bioactive molecules.     

Facile, chemoenzymatic synthesis of the potent antiviral compound, 2-acetonylinosine

A facile and efficient methodology for the chemoenzymatic synthesis of the antiviral compound, 2-acetonylinosine has been developed. The present synthetic strategy, which has generality, is a dramatic improvement on the methodologies currently available for the synthesis of functionalized purine nucleosides of therapeutic interest.     

On resin synthesis of sulfated oligosaccharides

Sulfated glycans are involved in many biological processes, making well-defined sulfated oligosaccharides highly sought molecular probes. These compounds are a considerable synthetic challenge, with each oligosaccharide target requiring specific synthetic protocols and extensive purifications steps. Here, we describe a general on resin approach that simplifies the synthesis of sulfated glycans. The oligosaccharide backbone, obtained by Automated Glycan Assembly (AGA), is subjected to regioselective sulfation and hydrolysis of protecting groups. The protocol is compatible with several monosaccharides and allows for multi-sulfation of linear and branched glycans. Seven diverse, biologically relevant sulfated glycans were prepared in good to excellent overall yield.

Well-defined sulfated oligosaccharides are important synthetic targets. We present an on resin approach for the synthesis of sulfated glycans with a broad reaction scope that overcomes previous limitations associated with on resin synthesis.     

Diastereoselective one-pot Wittig olefination-Michael addition and olefin cross metathesis strategy for total synthesis of cytotoxic natural product (+)-varitriol and its higher analogues

A stereoselective route for the total synthesis of anticancer marine natural product (+)-varitriol (1) is detailed herein. The impressive biological activity and interesting structural features of natural (+)-varitriol fuelled us to undertake the synthesis of some higher analogues (1a-j) of this molecule. The key features of the synthetic strategy include one-pot Wittig olefination followed by a highly diastereoselective oxa-Michael addition to assemble stereochemically pure tetrasubstituted THF moiety of the natural varitriol and olefin cross metathesis to couple the aromatic part with tetrasubstituted THF moiety. The total synthesis of title natural product is efficient with 21.8% overall yield for 9 linear steps from D-ribose and thus facilitates the more scaled-up practical route for the synthesis of 1 and its analogues as well. The synthetic (+)-varitriol (1) and its analogues were screened for their cytotoxicity. The present synthetic approach paves the way for preparation of numerous analogues of the title natural product for drug development.     

Studies towards the total synthesis of Phostriecin

A synthetic approach toward the phostriecin, an antitumor natural product is described. The key features of the present synthesis are Wittig reaction, synthesis of homoallylic alcohol using Brown’s protocol (alkoxyallylboration) and RCM for the creation of unsaturated lactone moiety of phostriecin.     

A general, iterative, and modular approach toward carbohydrate libraries based on ruthenium-catalyzed oxidative cyclizations

Carbohydrates are an omnipresent class of highly oxygenated natural products. Due to their wide spectra of biological activities, they have been in the center of synthetic organic chemistry for more than 130 years. During the past 50 years non-natural carbohydrates attracted the interest of various chemists in the fields of organic, biological, and medical chemistry. Especially desoxygenated sugars proved to be an important class of compounds. Up to date, most non-natural analogues are synthesized starting from natural, enantiomerically pure carbohydrates in multistep synthesis. In this report, we present a synthetic strategy that allows the selective modular synthesis of natural and non-natural carbohydrates within five synthetic steps starting from readily available starting materials. Due to a sequential introduction of O- or N-functionalities, a regioselective protection of each new functional group is possible. The key step in the carbohydrate synthesis is a RuO4-catalyzed oxidative cyclization via a pH-dependent dehydrogenation-dihydroxylation-cyclization or an oxidative fragmentation-cyclization, leading to highly substituted new carbohydrates, in which each functional group is orthogonally protected and accessible for further synthetic operations.     

Total Synthesis of Echinoside A,a Representative Triterpene Glycoside of Sea Cucumbers

Echinoside A, a sulfonylated holostane tetrasaccharide with potent anticancer and antifungal activity, was synthesized in a longest linear sequence of 35 steps and 0.6 % overall yield. The synthetic approach is adaptable to the synthesis of congeners and analogues, as exemplified by the ready synthesis of ds‐echinoside A and echinoside B, and thus will facilitate in‐depth studies on the promising biological effects of echinoside A. Moreover, the present synthesis demonstrates the feasibility of synthetic access to the characteristic complex triterpene glycosides that occur ubiquitously in sea cucumbers.     

Total Synthesis of Echinoside A,a Representative Triterpene Glycoside of Sea Cucumbers

Echinoside A, a sulfonylated holostane tetrasaccharide with potent anticancer and antifungal activity, was synthesized in a longest linear sequence of 35 steps and 0.6 % overall yield. The synthetic approach is adaptable to the synthesis of congeners and analogues, as exemplified by the ready synthesis of ds-echinoside A and echinoside B, and thus will facilitate in-depth studies on the promising biological effects of echinoside A. Moreover, the present synthesis demonstrates the feasibility of synthetic access to the characteristic complex triterpene glycosides that occur ubiquitously in sea cucumbers.     

Synthetic studies of cyclic peptides stephanotic acid methyl ester,celogentin C,and moroidin

An account of the total synthesis of stephanotic acid methyl ester and celogentin C is presented. The present synthesis features a tandem asymmetric Michael addition/bromination sequence for the synthesis of leucine-tryptophan moiety, and an oxidative coupling reaction to form the tryptophan-imidazole linkage. Moreover, the total synthesis of moroidin had also been studied, and three different synthetic strategies for the construction of the right-hand ring of moroidin were studied.     

Synthesis of Pyrazole Derivatives Possessing Anticancer Activity: Current Status

Pyrazole is a versatile lead compound to design potent bioactive molecules for drug discovery and development, particularly in cancer therapy. The aim of this review is to present the most recent deeds in the field of synthetic route made for functionalized pyrazole derivatives active against cell proliferation disease. The review article covers the synthesis of 1H-pyrazole, synthesis of N-substituted pyrazoles, synthesis of pyrazolopyrazoles, and synthesis of pyrazoles fused with a naturally occurring moiety. Some of these reported compounds have passed the preclinical or initial-phase clinical trials for their anticancer activity.     

Cu(II)-catalyzed decarboxylation/elimination of N-arylsulfonyl amino acids to primary aryl sulfonamides

A novel protocol for CuO-catalyzed decarboxylation/elimination of N-arylsulfonyl amino acids was developed. It is the first example of using an accessible amino acid as an ammonia synthetic equivalent for the synthesis of primary aryl sulfonamides via oxidative decarboxylation/elimination reactions. The present protocol shows excellent functional group tolerance and provides an efficient method for the synthesis of primary aryl sulfonamides in excellent yields.     

Gold and silver assisted synthesis of five-membered oxygen and nitrogen containing heterocycles

The investigation of methods for the chemical synthesis is a growing area of interest due to increasing environmental issues. The use of catalysts in organic reactions has gained extensive interest. Metal and nonmetal catalysts provided a new improved alternative to traditional methods in modern synthetic chemistry. The aim of the present review is to focus on the applications of gold- and silver-catalytic systems for the synthesis of five-membered oxygen- and nitrogen-heterocycles.     

A short and efficient synthesis of the tRNA nucleosides PreQ0 and archaeosine

Modified nucleosides in tRNAs play an important role in the translational process. They fine tune the codon-anticodon interactions and they influence the folding and stabilisation of the tRNA structure. Herein, we present a novel synthetic route to the highly modified nucleosides PreQ(0) and archaeosine. The synthesis involves coupling of a protected 7-cyano-7-deazaguanosine nucleobase with a TBDMS and isopropylidene protected chloro-ribose unit yielding the PreQ(0) nucleoside after deprotection. This PreQ(0) nucleoside is then used as the starting material for the synthesis of archaeosine providing the first total synthetic access to this hypermodified RNA nucleoside.     

Application of silver-promoted reactions in the synthesis of five-membered O-heterocycles

The investigation of facial protocols for chemical synthesis is a growing area of interest due to increasing environmental issues. The use of catalysts in organic reactions has gained extensive interest. Metal and nonmetal catalysts provided a new improved alternative to traditional methods in modern synthetic chemistry. The aim of the present review is to focus on the applications of silver-promoted reactions for the synthesis of oxygen containing five-membered heterocycles which have significance in organic synthesis, pharmaceuticals, agrochemicals, and among others.     

Recent advances in indoline synthesis

Indoline is an important structural motif present in several biologically active compounds from both natural and synthetic origins. The occurrence of this heterocyclic unity in these compounds is closely related to the biological activities they exhibit. This fact stimulated efforts that have been made worldwide to develop new synthetic approaches to prepare indolines. In this paper we reviewed critically the methods for indoline synthesis developed in the last years (from 2010 to 2018).     

Supported palladium nanoparticle‐catalysed Suzuki–Miyaura cross‐coupling approach for synthesis of aminoarylbenzosuberene analogues from natural precursor

A semi‐synthetic method has been developed for the synthesis of aminoarylbenzosuberenes (AABs) from naturally occurring himachalenes, an isomeric mixture of sesquiterpenes present in Cedrus deodara oil. Polymer‐stabilized Pd(0) nanoparticle‐catalysed Suzuki–Miyaura cross‐coupling reaction of aminovinyl bromide‐substituted benzosuberenes has been adopted for AAB synthesis. The catalyst performed well with different amine substituents, and was recycled up to five times. The synthesis of such arylated benzosuberene class of compounds from natural precursors following semi‐synthetic approaches could provide an attractive alternative method with reduced number of steps.     

Assembly of Terpenoid Cores by a Simple,Tunable Strategy

Oxygenated, polycyclic terpenoid natural products have important biological activities. Although total synthesis of such terpenes is widely studied, synthetic strategies that allow for controlled placement of oxygen atoms and other functionality remains a challenge. Herein, we present a simple, scalable, and tunable synthetic strategy to assemble terpenoid‐like polycycloalkanes from cycloalkanones, malononitrile, and allylic electrophiles, abundantly available reagent classes.