Stereoselective cyclopropanation of serine- and threonine-derived oxazines to access new morpholine-based scaffolds

Organocatalytic Desymmetric Double Aza-Michael Addition Cascade: Enantioselective Synthesis of Fused Morpholines

Double aza-Michael addition (DAM) has become an emerging strategy for the construction of two carbon-nitrogen bonds in a single step, which can significantly simplify the synthesis of N-heterocycles. Hitherto, their asymmetric catalytic genre remains unattempted. Herein, we describe the judicious design of an organocatalytic enantioselective desymmetric double aza-Michael addition cascade to access a series of functionalized fused morpholines with excellent yields and diastereo- and enantioselectivities. A one-pot telescopic synthesis was demonstrated for a bridged triheterocyclic compound. In addition, scale-up synthesis and various attractive postsynthetic modifications of the title products amplify the significance of the current methodology.

Synthesis of Oxazolidines and Dihydroxazines via Cyclization of α-Aminated Ketones

A new approach to oxazolidines and dihydroxazines was developed by regioselective cyclization of α-aminated ketones under transition metal-free conditions. Oxazolidine derivatives were generated in the presence of chloro benziodoxole and TFA, while dihydroxazines were formed without a hypervalent iodine reagent. The reaction was performed under room temperature and gave the products in good to excellent yields.

Synthetically-tailored and nature-derived dual COX-2/5-LOX inhibitors: Structural aspects and SAR

Inflammation is a most complex pathological process that gives birth to different diseases. Different inflammatory mediators are released during an inflammation responsible for acute pain and chronic inflammatory diseases like cancer, asthma, rheumatoid arthritis, osteoarthritis, neurodegenerative diseases, metabolic and cardiovascular disorders. The arachidonic acid pathway, which results in the production of inflammatory mediators, provides several targets for anti-inflammatory intervention. The most popularly used medications for inflammation are non-steroidal anti-inflammatory agents (NSAIDs) but it has some limitations, in particular traditional NSAIDs which inhibit the COX pathway non-selectively, producing gastrointestinal side effects, and other adverse effects like stroke and renal failure. On the other hand, selective COX-2 inhibitors commonly known as 'coxibs' produce cardiovascular side effects. Frequent inhibition of either cyclooxygenase or lipoxygenase enzyme switches the metabolism of arachidonic acid from one to another which could lead to serious consequences. Therefore, a need to develop novel, effective and safe anti-inflammatory agents which can inhibit the release of both prostaglandins and leukotrienes from the respective cyclooxygenase and lipoxygenase pathways has emerged. This resulted in the discovery of new anti-inflammatory agents derived from natural and synthetic sources as dual COX-2/5-LOX inhibitors. To further contribute towards the discovery in this field, we have attempted to summarize structural features and pharmacological activities of heterocyclic scaffolds and natural products explored as dual COX-2/5-LOX inhibitors. We have emphasized the designing of the dual inhibitors inspired by the previously reported COX-2 and 5-LOX inhibitors. This outline could render us to identify the best pharmacophores catering to dual COX-2/5-LOX inhibitory activity while improving their efficiency as anti-inflammatory agents.

Dihydropyrazole Derivatives Containing Benzo Oxygen Heterocycle and Sulfonamide Moieties Selectively and Potently Inhibit COX-2: Design, Synthesis, and Anti-Colon Cancer Activity Evaluation

Cyclooxygenase-2 (COX-2) as a rate-limiting metabolism enzyme of arachidonic acid has been found to be implicated in tumor occurrence, angiogenesis, metastasis as well as apoptosis inhibition, regarded as an attractive therapeutic target for cancer therapy. In our research, a series of dihydropyrazole derivatives containing benzo oxygen heterocycle and sulfonamide moieties were designed as highly potent and selective COX-2 inhibitors by computer-aided drug analysis of known COX-2 inhibitors. A total of 26 compounds were synthesized and evaluated COX-2 inhibition and pharmacological efficiency both in vitro and in vivo with multi-angle of view. Among them, compound 4b exhibited most excellent anti-proliferation activities against SW620 cells with IC₅₀ of 0.86 ± 0.02 µM than Celecoxib (IC₅₀ = 1.29 ± 0.04 µM). The results favored our rational design intention and provides compound 4b as an effective COX-2 inhibitor available for the development of colon tumor therapeutics.

Diversity-Oriented Synthesis and Chemoinformatic Analysis of the Molecular Diversity of sp3-Rich Morpholine Peptidomimetics

Diversity-Oriented Synthesis (DOS) consists of generating structurally diverse compounds from a complexity-generating reaction followed by cyclization steps and appendage diversity. DOS has gathered interest to systematically explore the chemical space by generating high-quality small-molecule collections as probes to investigate biological pathways. The generation of heterocycles using amino acid and sugar derivatives as building blocks is a powerful approach to access chemical and geometrical diversity thanks to the high number of stereocenters and the polyfunctionality of such compounds. Our efforts in this field are focused on the generation of diversity-oriented molecules of peptidomimetic nature as a tool addressing protein-protein interactions, taking advantage of amino acid- and sugar-derived polyfunctional building blocks to be applied in couple-pair synthetic approaches. In this paper, the combination of diversity-oriented synthesis and chemoinformatics analysis of chemical space and molecular diversity of heterocyclic peptidomimetics are reported, with particular interest toward carbohydrate- and amino acid-derived morpholine scaffolds with a higher fraction of sp3 carbon atoms. Also, the chemoinformatic analysis of chemical space and molecular diversity of 186 morpholine peptidomimetics is outlined.

Stereoselective Polymer-Supported Synthesis of Morpholine- and Thiomorpholine-3-carboxylic Acid Derivatives

Herein we report the polymer-supported synthesis of 3,4-dihydro-2H-1,4-oxazine-3-carboxylic acid derivatives using immobilized Fmoc-Ser(tBu)-OH and Fmoc-Thr(tBu)-OH as the starting materials. After the solid-phase-synthesis of N-alkyl-N-sulfonyl/acyl intermediates, the target dihydrooxazines were obtained using trifluoroacetic acid-mediated cleavage from the resin. This approach was also studied for the preparation of dihydrothiazines from immobilized Fmoc-Cys(Trt)-OH. Inclusion of triethylsilane in the cleavage cocktail resulted in the stereoselective formation of the corresponding morpholine/thiomorpholine-3-carboxylic acids. Stereochemical studies revealed the specific configuration of the newly formed stereocenter and also the formation of stable N-acylmorpholine rotamers.

Short synthesis of polyfunctional sp3-rich threonine-derived morpholine scaffolds

A convenient synthesis of sp³-rich complex morpholines was achieved in two steps involving a Petasis three-component coupling reaction followed by an acid- or base-mediated cyclization.

Amino acid chirons: a tool for asymmetric synthesis of heterocycles

As a result of their easy availability in enantiomerically enriched form and their possession of synthetically transformable diverse functional groups, amino acids have been extensively used by synthetic organic and medicinal chemists as a chiral pool for access to heterocycles (monocycles, bicycles or polycycles, either bridged or fused). This review describes the syntheses of diverse asymmetric heterocycles with various membered rings (n = 3-9) followed by benzo or heteroannulated ones, for the period from 1996 to Dec. 2013. It details solution phase synthetic methodologies in which the naturally occurring α-amino acid is incorporated, totally or partially, into the final product.

Two-step one-pot synthesis of dihydropyrazinones as Xaa-Ser dipeptide isosteres through morpholine acetal rearrangement

The synthesis of the uncommon dihydropyrazinone ring was accomplished by taking advantage of the ring rearrangement ofN-acylated morpholine acetal derived from serine under acidic treatment and in the presence of 2,6-lutidine, resulting in a constrained Xaa-Ser dipeptide isostere.