Synthesis of morpholine derivatives using the Castagnoli-Cushman reaction as BACE1 inhibitors: Unexpected binding activity of cyclic thioamides

The Castagnoli-Cushman reaction between diglycolic anhydride and imines was applied for the synthesis of morpholine derivatives containing a thioamide or an amidino group. Enzyme inhibition assays towards BACE1 revealed an unexpected role of the cyclic thioamide group in providing inhibition in the micromolar range. Molecular docking calculations showed the thioamido group interacting with catalytic aspartic acid, and calculated BBB permeability indicated this molecular scaffold as a promising hit for further optimization.

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 Synthesis of Benzo[e][1,4]oxazino[4,3-a][1,4]diazepine-6,12-diones with Two Diversity Positions

Herein, we report a stereoselective formation of tetrahydro-6H-benzo[e][1,4]oxazino[4,3-a][1,4]diazepine-6,12(11H)-diones. Their preparation consisted in solid-phase synthesis of linear intermediates starting from polymer-supported Ser(tBu)-OH. Using various 2-nitrobenzoic acids and bromoketones, the key intermediates were obtained in five steps and subjected to trifluoroacetic acid-mediated cleavage from the resin, followed by stereoselective reduction with triethylsilane. Subsequent catalytic hydrogenation of the nitro group and cyclization yielded the target compounds with full retention of the C^12a stereocenter configuration.

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.

Breaking aziridines to construct morpholines with a gold(i)-catalyzed tandem ring-opening and cycloisomerization reaction

A convenient synthetic method for the construction of morpholine derivatives from easily available aziridines and propargyl alcohols has been successfully developed. A tandem nucleophilic ring-opening of aziridine/6-exo-dig cyclization/double bond isomerization sequence was achieved by using a single gold(i) catalyst under mild conditions. The gold(i) catalyst served as a π acid and also a σ acid to realize the dual activation of both reactants in this reaction. The obtained unsaturated morpholine products could be easily hydrogenated to achieve target morpholine derivatives with good diastereoselectivities in high yields.

Carbohydrates in diversity-oriented synthesis: challenges and opportunities

Carbohydrates are attractive building blocks for diversity-oriented synthesis due to their stereochemical diversity and high density of polar functional groups.

Intramolecular functional group differentiation as a strategy for the synthesis of bridged bicyclic β-amino acids

Differentiation of identical electrophilic functional groups (carboxylates) by a strategically placed internal nucleophile (an amino group) in cyclic precursors was used as a key general approach to functionalized azabicyclic scaffolds.

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.

Diversity-oriented synthesis as a tool for chemical genetics

Chemical genetics is an approach for identifying small molecules with the ability to induce a biological phenotype or to interact with a particular gene product, and it is an emerging tool for lead generation in drug discovery. Accordingly, there is a need for efficient and versatile synthetic processes capable of generating complex and diverse molecular libraries, and Diversity-Oriented Synthesis (DOS) of small molecules is the concept of choice to give access to new chemotypes with high chemical diversity. In this review, the combination of chemical genetics and diversity-oriented synthesis to identify new chemotypes as hit compounds in chemical biology and drug discovery is reported, giving an overview of basic concepts and selected case studies.