Skeletal diversity by sequential one-pot and stepwise routes using morpholine ester scaffolds

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.

Combination of multicomponent KA2 and Pauson-Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

The Cu-catalyzed multicomponent ketone–amine–alkyne (KA²) reaction was combined with a Pauson–Khand cycloaddition to give access of unprecedented constrained spirocyclic pyrrolocyclopentenone derivatives following a DOS couple-pair approach. The polyfunctional molecular scaffolds were tested on the cyclopentenone reactivity to further expand the skeletal diversity, demonstrating the utility of this combined approach in generating novel spiro compounds as starting material for the generation of chemical libraries. The chemoinformatics characterization of the newly-synthesized molecules gave evidence about structural and physicochemical properties with respect to a set of blockbuster drugs, and showed that such scaffolds are drug-like but more spherical and three-dimensional in character than the drugs.

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.

Traceless Solid-Phase Synthesis of [6,7,8 + 5,6,7]-Fused Molecular Frameworks

We report two synthetic strategies for traceless solid-phase synthesis of molecular scaffolds comprising 6- to 8-membered rings fused with 5- to 7-membered rings. Traceless synthesis facilitated preparation of target molecules without any trace of polymer-supported linkers. The cyclization proceeded via acid-mediated tandem N-acylium ion formation followed by the nucleophilic addition of O- and C-nucleophiles. The presented synthetic strategy enabled, through the use of simple building blocks without any conformational preferences, the evaluation of the predisposition of different combinations of ring sizes to form fused ring molecular scaffolds. Compounds with any combination of [6,7 + 5,6,7] ring sizes were accessible with excellent crude purity. The 8-membered cyclic iminium was successfully fused only with the 5-membered cycle and larger fused ring systems were not formed, probably due to their instability.

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.

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.

Polymer-supported stereoselective synthesis of tetrahydro-2H-oxazolo[3,2-a]pyrazin-5(3H)-ones from N-(2-oxo-ethyl)-derivatized dipeptides via eastbound iminiums

Polymer-supported N-(2-oxo-ethyl)-derivatized Ser/Thr/Cys-containing dipeptides were synthesized and subjected to acid-mediated tandem N-acylium ion cyclization-nucleophilic addition to yield tetrahydro-2H-oxazolo[3,2-a]pyrazin-5(3H)-ones. The reaction conditions and building-block combinations for stereoselective synthesis of the newly formed asymmetric carbon were developed. The synthesis was fully compatible with solid-phase peptide synthesis, and the products serve as conformationally constrained peptidomimetics. The traceless synthesis of bicycles is also reported as part of this work.