Experimental and Theoretical Studies on Stereo- and Regioselectivity in Intramolecular Nitrone−Alkene Cycloaddition of Hept-6-enoses Derived from Carbohydrates

Synthesis of Uronic Acid 1-Azasugars as Putative Inhibitors of α-Iduronidase, β-Glucuronidase and Heparanase

1-Azasugar analogues of l-iduronic acid (l-IdoA) and d-glucuronic acid (d-GlcA) and their corresponding enantiomers have been synthesized as potential pharmacological chaperones for mucopolysaccharidosis I (MPS I), a lysosomal storage disease caused by mutations in the gene encoding α-iduronidase (IDUA). The compounds were efficiently synthesized in nine or ten steps from d- or l-arabinose, and the structures were confirmed by X-ray crystallographic analysis of key intermediates. All compounds were inactive against IDUA, although l-IdoA-configured 8 moderately inhibited β-glucuronidase (β-GLU). The d-GlcA-configured 9 was a potent inhibitor of β-GLU and a moderate inhibitor of the endo-β-glucuronidase heparanase. Co-crystallization of 9 with heparanase revealed that the endocyclic nitrogen of 9 forms close interactions with both the catalytic acid and catalytic nucleophile.

Asymmetric Total Synthesis of Hasubanan Alkaloids: Periglaucines A-C, N,O-Dimethyloxostephine and Oxostephabenine

We report herein the asymmetric total synthesis of periglaucines A-C, N,O-dimethyloxostephine and oxostephabenine. The key strategies used include: 1) a Rh^I -catalyzed regio- and diastereoselective Hayashi-Miyaura reaction to connect two necessary fragments; 2) an intramolecular photoenolization/Diels-Alder (PEDA) reaction to construct the highly functionalized tricyclic core skeleton bearing a quaternary center; 3) a bio-inspired intramolecular Michael addition and transannular acetalization to generate the aza[4.4.3]propellane and the tetrahydrofuran ring.

Recent progress in the synthesis of the furanosteroid family of natural products

This review focuses on an overview of recent advances in the synthesis of furanosteroids and illustrates their applications in medicinal chemistry over the period of 2005–present.

Isoxazolidine: A Privileged Scaffold for Organic and Medicinal Chemistry

The isoxazolidine ring represents one of the privileged structures in medicinal chemistry, and there have been an increasing number of studies on isoxazolidine and isoxazolidine-containing compounds. Optimization of the 1,3-dipolar cycloaddition (1,3-DC), original methods including electrophilic or palladium-mediated cyclization of unsaturated hydroxylamine, has been developed to obtain isoxazolidines. Novel reactions involving the isoxazolidine ring have been highlighted to accomplish total synthesis or to obtain bioactive compounds, one of the most significant examples being probably the thermic ring contraction applied to the total synthesis of (±)-Gelsemoxonine. The unique isoxazolidine scaffold also exhibits an impressive potential as a mimic of nucleosides, carbohydrates, PNA, amino acids, and steroid analogs. This review aims to be a comprehensive and general summary of the different isoxazolidine syntheses, their use as starting building blocks for the preparation of natural compounds, and their main biological activities.

Intramolecular direct aldol reactions of sugar 2,7-diketones: syntheses of hydroxylated cycloalka(e)nones

A regio- and stereoselective intramolecular direct aldol reaction of 2,7-diketones derived from carbohydrates has been developed to construct cycloalkanones 7, which were dehydrated to obtain heavily oxygenated cycloalkenones 8.

Facile and enantiospecific syntheses of (6S,7R)-6-chloro-7-benzyloxy-, (7S)-halo-, and (7S)-hydroxy-cocaine and natural (-)-cocaine from D-(-)-ribose

First syntheses of C6,7 and C7 enantiopure cocaine analogues were achieved from D-(-)-ribose via a trans-acetonide controlled endo-selective intramolecular nitrone-alkene cycloaddition (INAC) as the key step. This synthetic scheme allows practical preparation of cocaine analogues for bioevaluation as potential candidates for the treatment of cocaine addiction and as potential conjugates for immunotherapy.

Expanding stereochemical and skeletal diversity using petasis reactions and 1,3-dipolar cycloadditions

A short and modular synthetic pathway using intramolecular 1,3-dipolar cycloaddition reactions and yielding functionalized isoxazoles, isoxazolines, and isoxazolidines is described. The change in shape of previous compounds and those in this study is quantified and compared using principal moment-of-inertia shape analysis.

Antibacterial activity, quantitative structure-activity relationship and diastereoselective synthesis of isoxazolidine derivatives via 1,3-dipolar cycloaddition of d-glucose derived nitrone with olefin

The diastereoselectivity of the intermolecular 1,3-dipolar cycloaddition reaction of d-glucose-derived nitrones with both cyclic and acyclic dipolarophiles were studied. The reaction of nitrone with acyclic dipolarophiles resulted in the formation of the endo adduct exclusively whereas with cyclic dipolarophiles endo adduct was obtained as the major product. Antibacterial activity was evaluated for these eighteen isoxazolidine derivatives against Staphylococcus aureus NCIM5021, Escherichia coli NCIM 2931 and Pseudomonas aeruginosa NCIM 5029 by twofold dilution technique using resazurin as the indicator dye. Quantitative structureactivity relationships were developed with fourteen and the model was validated with four data. Electronic and spatial descriptors were the major contributors in all the three quantitative structureactivity relationship equations and the statistical parameters r(2), r(2)(adj) , F-ratio and q(2) were found to be satisfactory.

Skeletally diverse small molecules using a build/couple/pair strategy

Intermolecular couplings of simple building blocks using catalytic, stereoselective cross-Mannich reactions followed by intramolecular functional group-pairing reactions of easily accessed variants of the Mannich products are explored as a route to skeletally diverse small molecules. The synthetic pathway yields products having 12 different skeletons using only three steps and has the potential to enable substantial stereochemical diversification in the future.

Intramolecular direct aldol reactions of sugar diketones: syntheses of valiolamine and validoxylamine G

A new and stereoselective intramolecular direct aldol reaction of diketones derived from carbohydrates has been developed to construct carbocycles with D-gluco-, D-galacto-, D-manno-, and L-ido-configurations. The stereochemical outcome of the aldol reaction of the diketone is dependent on the base used. Transformation of D-gluco-aldols readily affords valiolamine which also constitutes a formal synthesis of voglibose. Facile conversion of D-gluco-cyclohexanones into validoxylamine G has been achieved in 12 steps with 15.1% overall yield from D-glucose.

A Fascination with 1,2-Diacetals

1,2-Diacetals are readily prepared, rigid structural motifs that provide a wide range of opportunities for applications in natural product assembly. These uses encompass selective 1,2-diol or alpha-hydroxy acid protection, enantiotopic recognition and desymmetrization methods, chiral memory applications, and reactivity control in oligosaccharide synthesis, as well as functioning as templating components, chiral auxiliaries, and building blocks. 1,2-Diacetals are often more stable and lead to products with enhanced crystallinity compared to their five-ring acetonide counterparts. Many 1,2-diacetals have favorable NMR parameters, which facilitate structural assignment, particularly during asymmetric reaction processes.