Stereoselective syntheses of the glycosidase inhibitors hyacinthacine A2, hyacinthacine A3 and 5-epi-hyacinthacine A3

Recent advances in the total synthesis of polyhydroxylated alkaloids via chiral oxazines

This review summarizes recently established methodologies developed for the enantioselective and diastereoselective synthesis of chiral 1,3-oxazines. These compounds are of interest as advanced synthetic intermediates in the total synthesis of structurally complex and biologically active polyhydroxylated alkaloids such as (+)-1-deoxynojirimycin, (-)-anisomycin, (+)-castanospermine, (+)-casuarine, (-)-conduramine F-1, (-)-sphingofungin B, Neu5Ac methyl ester, and other natural products. The devised synthetic approach aims to offer a direct, efficient, and adaptable method for obtaining both pure enantiomers and pure diastereomers. It revolves around utilizing chiral building blocks like syn,syn-, syn,syn,anti-, syn,anti-, syn,anti,syn-, anti,syn-, anti,syn,syn-, and anti,syn,anti-oxazines. By integrating oxazine chemistry with established and innovative transformations, this approach enabled the synthesis of 30 polyhydroxylated amines across various studies conducted between 2007 and 2022.

Chirality extension of an oxazine building block en route to total syntheses of (+)-hyacinthacine A2 and sphingofungin B

Concise total syntheses of (+)-hyacinthacine A₂ and sphingofungin B were achieved by palladium(0)-catalyzed intramolecular oxazine formation and diastereoselective nucleophilic additions.

Pyrrolizidine alkaloids

This review covers pyrrolizidine alkaloids isolated from natural sources. Topics include: aspects of structure, isolation, and biological/pharmacological studies; total syntheses of necic acids, necine bases and closely-related non-natural analogues.

Methyl (3aRS,3cRS,6cSR,7RS,8RS,8aSR)-2,5-bis(4-chlorophenyl)-7,9-bis(1,3-diphenyl-1H-pyrazol-4-yl)-1,3,4,6-tetraoxododecahydro-1H-dipyrrolo[3,4-a:3',4'-f]pyrrolizine-3b-carboxylate dimethylformamide disolvate: a three-dimensional hydrogen-bonded framework

The racemic title dipyrrolopyrrolizine compound crystallizes from dimethylformamide as a disolvate, C(55)H(39)Cl(2)N(7)O(6)·2C(3)H(7)NO. None of the four fused heterocyclic rings is planar; one adopts an envelope conformation, two others adopt half-chair conformations and the fourth adopts a conformation intermediate between an envelope and a half-chair. The arrangement of the ring fusions is such as to preclude the possibility of internal mirror symmetry. The three independent molecular components are weakly linked by C-H···O hydrogen bonds, and the dipyrrolopyrrolizine molecules are linked by a combination of four C-H···O and one C-H···π(arene) hydrogen bond to form a three-dimensional framework, from which the dimethylformamide solvent molecules are pendent. However, aromatic π-π stacking interactions are absent in the structure.

Total Synthesis of Hyacinthacine A2: Stereocontrolled 5-aza-cyclooctene Photoisomerization and Transannular Hydroamination with Planar-to-Point Chirality Transfer

The total synthesis of hyacinthacine A2 is reported via a novel transannular hydroamination in which planar chirality of a 5-aza-trans-cyclooctene precursor is transferred to point chirality in the product. Key to the success of this strategy was the development of a method for establishing absolute planar chirality via stereocontrolled photoisomerization of a 5-aza-cis-cyclooctene. This was accomplished by constructing a 5-aza-cis-cyclooctene precursor with a trans-fused acetonide. The improved diastereoselectivity observed upon photoisomerization of this derivative is attributed to the conformational strain of the eight-membered ring in the minor diastereomer.