Enantiopure Cyclic Nitrones Research Articles

Alkoxyallene-Based Stereodivergent Syntheses of (-)-Hyacinthacine B4 and of Putative Hyacinthacine C5 Epimers: Proposal of Hyacinthacine C5 Structure.

Hyacinthacines are members of the class of polyhydroxylated pyrrolizidines exhibiting outstanding biological activity as glycosidases inhibitors. Their structural complexity is embodied in the densely functionalized core, possessing a series of contiguous stereogenic centers. In this synthetic study we report a route to the more complex congeners of this class of alkaloids exploiting the diastereoselective addition of an axially chiral lithiated alkoxyallene to an enantiopure cyclic nitrone. Our stereodivergent approach enabled the installation of the targeted configuration at the ring A by minimal synthetic manipulations and at ring B by using stage dependent selective functionalizations. The versatility and robustness of this methodology were demonstrated by the syntheses of (-)-hyacinthacine B4 and of two epimers of (+)-hyacinthacine C5, allowing a suggestion of the likely structure of the isolated natural product.

Inexpensive, multigram-scale preparation of an enantiopure cyclic nitrone via resolution at the hydroxylamine stage

The reduction of the chiral, racemic nitrone MiPNO provides a secondary hydroxylamine. Its O-acylation with O, O’-dibenzoyl- l-tartaric acid anhydride gives two diastereomers, that can be easily separated by selective dissolution in orthogonal solvents. The recovery of the enantiopure nitrone is then carried out in a single step. The process allows the straightforward isolation of ( R) and ( S)-MiPNO in 57% and 38% yield, respectively, from rac-MiPNO.

ChemInform Abstract: Synthesis of Enantiopure Protected 3-Hydroxy-4-amino Pyrroline N-Oxides.

Abstract The synthesis of new five-membered enantiopure cyclic nitrones bearing protected cis vicinal amino and hydroxy functionalities is reported. The key step was a Mitsunobu reaction, which allowed placement of an azido group, with inversion of configuration, at the reacting centre. Cycloaddition of the novel nitrones to but-3-en-1-ol followed by simple elaboration of the adducts readily afforded protected amino dihydroxy indolizidines.

Application of Chiral Cyclic Nitrones to the Diastereoselective Synthesis of Bicyclic Isoxazolidine Nucleoside Analogues

New bicyclic isoxazolidine nucleoside analogues are synthesized through 1,3-dipolar cycloaddition of enantiopure cyclic nitrones to appropriate vinyl nucleobases. The reactions are diastereoselective, giving as the main or the sole product the exo-Re cycloadducts. The diastereoselectivity depends on both the kind of the base and the substitution pattern of the nitrone.

Enantiopure Cyclic Nitrones: A Useful Class of Building Blocks for Asymmetric Syntheses

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Enantiopure Cyclic Nitrones: A Useful Class of Building Blocks for Asymmetric Syntheses

The synthesis of enantiopure cyclic nitrones has become a frequently addressed topic in discussions of their usefulness in the production of natural products and biologically active compounds. This emphasis has stimulated the development of a variety of synthetic approaches that are described in this review, organized on the basis of the size of the nitrone ring.

New chiral nitrones as precursors of α,α-disubstituted amino-acids, according to the SRS principle

The preparation of new enantiopure cyclic nitrones based on the 1-oxy-2,3-dihydro-imidazol-4-one ring is described. The addition of arylmagnesium or alkynylzinc reagents to these nitrones can be achieved with total enantio- and diastereoselectivity, leading to α,α-disubstituted amino-acid precursors.

Tandem Addition/Cyclization of Alkynylzinc Reagents to Enantiopure 2‐tert‐Butyl‐3,5‐dimethyl‐2,3‐dihydroimidazol‐4‐one N‐Oxide: Potential Precursors of Quaternary α‐Amino Acids.

A new enantiopure cyclic nitrone, a potential electrophilic alanine synthon, has been prepared. Its reaction with alkynylzinc reagents led to a tandem addition/cyclization reaction with complete regio- and stereoselectivity. The adducts are potential precursors of quaternary α-amino acids. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Tandem Addition/Cyclization of Alkynylzinc Reagents to Enantiopure 2‐tert‐Butyl‐3,5‐dimethyl‐2,3‐dihydroimidazol‐4‐one N‐Oxide: Potential Precursors of Quaternary α‐Amino Acids

AbstractA new enantiopure cyclic nitrone, a potential electrophilic alanine synthon, has been prepared. Its reaction with alkynylzinc reagents led to a tandem addition/cyclization reaction with complete regio‐ and stereoselectivity. The adducts are potential precursors of quaternary α‐amino acids. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Stereoselective synthesis of new bicyclic N, O- iso-homonucleoside analogues

The synthesis of two new bicyclic nucleoside analogues is reported. These compounds are iso-homonucleoside and are synthesised through a 1,3-dipolar cycloaddition of an enantiopure cyclic nitrone to protected allyl acohol and subsequent introduction of thymine by a Mitsunobu reaction.

Synthesis and 1,3‐Dipolar Cycloadditions of a New Enantiopure Cyclic Nitrone.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and 1,3-dipolar cycloadditions of a new enantiopure cyclic nitrone

A new enantiopure cyclic nitrone has been efficiently synthesized from a d-glyceraldehyde derivative. Its 1,3-dipolar cycloaddition to different classes of dipolarophiles show complete antifacial selectivity, furnishing highly functionalized enantiopure bicyclic isoxazolidines.

Synthesis of enantiopure protected 3-hydroxy-4-amino pyrroline N-oxides

The synthesis of new five-membered enantiopure cyclic nitrones bearing protected cis vicinal amino and hydroxy functionalities is reported. The key step was a Mitsunobu reaction, which allowed placement of an azido group, with inversion of configuration, at the reacting centre. Cycloaddition of the novel nitrones to but-3-en-1-ol followed by simple elaboration of the adducts readily afforded protected amino dihydroxy indolizidines.

ChemInform Abstract: Straightforward Synthesis of (1→2)‐Linked Pseudo Aza‐C‐disaccharides by the Novel Cycloaddition of Enantiopure Cyclic Nitrones to Glycals.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Straightforward Synthesis of (1-->2)-Linked Pseudo Aza-C-disaccharides by the Novel Cycloaddition of Enantiopure Cyclic Nitrones to Glycals.

The novel, highly stereoselective, intermolecular cycloaddition reaction of enantiopure cyclic nitrones 8 to 1,2-glycals 9 opens the way to a straightforward synthesis of a broad class of new (1-->2)-linked pseudo aza-C-disaccharides 6, suitable substrates for selective inhibition of glycosidase enzymes. The cycloadditions occur with high stereocontrol, displaying preferential interaction between the bottom face of the glycal and the face of the nitrone anti to the substituent on C-3, with the reagents approaching in an exo fashion. The cycloadditions produced tricyclic isoxazolidines 7 that represent nonreducing pseudo aza-C-disaccharides stable to hydrolytic conditions. The target pseudo aza-disaccharides 6 were obtained by sequential deprotection of the hydroxyl groups and isoxazolidine ring-opening.

New Access to Aza- C-disaccharides by Cycloadditions of Pyrroline N-Oxides to Glycals

A novel, highly stereoselective intermolecular cycloaddition reaction of simple and enantiopure cyclic nitrones to glucose and galactose-derived 1,2-glycals offers a direct access to a new class of pseudoaza-C-disaccharides with isoxazolidine structure, potential glycosidase inhibitors. The synthesis of new (1→2)-linked aza-disaccharides is accomplished by simple reductive ring-opening of the isoxazolidine. © 1997 Elsevier Science Ltd.

ChemInform Abstract: A Five‐Membered Enantiopure Cyclic Nitrone from Malic Acid by Regioselective Oxidation of Cyclic Hydroxylamine. Synthesis of (1S,7S, 8aR)‐Octahydro‐1,7‐dihydroxyindolizine.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A Five-Membered Enantiopure Cyclic Nitrone from Malic Acid by Regioselective Oxidation of Cyclic Hydroxylamine. Synthesis of (1S,7S,8aR)-Octahydro-1,7-dihydroxyindolizine

A Five-Membered Enantiopure Cyclic Nitrone from Malic Acid by Regioselective Oxidation of Cyclic Hydroxylamine. Synthesis of (1S,7S,8aR)-Octahydro-1,7-dihydroxyindolizine