Dihydroxylation-Based Approach for the Asymmetric Syntheses of Hydroxy-γ-butyrolactones

Retinestatin, a Polyol Polyketide from a Termite Nest-Derived Streptomyces sp

A new polyol polyketide, named retinestatin (1), was obtained and characterized from the culture of a Streptomyces strain, which was isolated from a subterranean nest of the termite Reticulitermes speratus kyushuensis Morimoto. The planar structure of 1 was elucidated on the basis of the cumulative analysis of ultraviolet, infrared, mass spectrometry, and nuclear magnetic resonance spectroscopic data. The absolute configuration of 1 at 12 chiral centers was successfully assigned by employing a J-based configuration analysis in combination with ROESY correlations, a quantum mechanics-based computational approach to calculate NMR chemical shifts, and a 3 min flash esterification by Mosher's reagents followed by NMR analysis. Biological evaluation of retinestatin (1) using an in vitro model of Parkinson's disease revealed that 1 protected SH-SY5Y dopaminergic cells from MPP+-induced cytotoxicity, indicating its neuroprotective effects.

Samarium Iodide-Promoted Asymmetric Reformatsky Reaction of 3-(2-Haloacyl)-2-oxazolidinones with Enals

3-(2-Haloacyl)-2-oxazolidinones were shown to react with enals in an asymmetric SmI₂-promoted Reformatsky reaction to give stereochemically well-defined 3-hydroxy-4-alkenyl- and 3-hydroxy-2-methyl-4-alkenyl imides. Chirality transfer of the Evans (S)-oxazolidinone unit via a Zimmerman-Traxler-like transition state resulted in Reformatsky products with a relative syn-configuration. The absolute configuration of compounds obtained is opposite to the corresponding products obtained via aldol addition of boron enolates to enals using the same Evans oxazolidinones.

SuperQuat chiral auxiliaries: design, synthesis, and utility

The design, synthesis and outline of some of the most common synthetic applications of the SuperQuat (4-substituted 5,5-dimethyloxazolidine-2-one) family of chiral auxiliaries, developed to address the shortcomings of the Evans (4-substituted oxazolidin-2-one) family of chiral auxiliaries, are presented.

Protective Effects of Compounds in Bombax ceiba flower on Benzo[a]pyrene-Induced Cytotoxicity

The methanolic extract of the flower of Bombax ceiba was found to show protective effects on cytotoxicity induced by benzo[a]pyrene (BaP) in HT1080 cells. We therefore tried to examine and estimate the active constituents. We isolated 16 compounds from the extract, including four butyrolactones and two ascorbic acid derivatives, as well as mangiferin. Among the isolated compounds, a butyrolactone derivative, (-)-loliolide, and two flavonoids, kaempferol 3- O-β-D-glucopyranoside and quercetin 3- O-β-D-glucopyranoside, protected the cells against the BaP-induced cytotoxicity. Quercetin, the aglycone of one of the active constituents, showed a weaker effect than its glycoside. This is the first report of the protective effects of the methanolic extract of B. ceiba and its constituents on BaP-induced cytotoxicity.

Total synthesis of cananginone C and structural revision of debilisone A

A short, convergent and general strategy for stereoselective total synthesis of biologically active α-substituted γ-hydroxymethyl γ-lactone based natural products cananginone C and debilisone A has been developed. The salient features of this synthesis include Cadiot-Chodkiewicz coupling, Evans allylation, Sharpless asymmetric dihydroxylation and γ-lactonization. The originally proposed structure of debilisone A has been revised.

Reverse regioselectivity in Pd(0)/InI-mediated allylation of aldehydes with ε-amido-allylindiums generated from β-lactams. A new entry to non-racemic highly substituted γ-butyrolactones

ε-Amido-allylindiums generated from β-lactams in the presence of 2 eq. of InI, catalytic amounts of Pd(PPh₃)₄ and 5 eq. of CF₃CO₂H react with a number of aromatic and aliphatic aldehydes to afford trisubstituted γ-butyrolactones in high yield.

Enantioselective synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from β-substituted β-hydroxyaminoaldehydes

The synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from β-substituted β-hydroxyaminoaldehydes is reported. The β-hydroxyaminoaldehydes were prepared by enantioselective organocatalytic 1,4-addition of N-tert-butyl (tert-butyldimethylsilyl)oxycarbamate to α,β-unsaturated aldehydes (MacMillan protocol). Alkyne addition to the aldehydes followed by alcohol oxidation furnished N-Boc O-TBS-protected β-aminoynones. Removal of the TBS protecting group initiated a 7-endo-dig cyclization to yield previously unknown 3,4-dihydro-1,2-oxazepin-5(2H)-ones. Reductive cleavage of the N-O bond of the oxazepinones and Boc-deprotection provided 2-substituted 2,3-dihydropyridin-4(1H)-ones via 6-endo-trig cyclization. 2,3-Dihydropyridin-4(1H)-ones are versatile intermediates that have been used for the synthesis of many alkaloids. The new protocol allows the synthesis of 3-dihydropyridin-4(1H)-ones carrying an array of substituents at C2 that cannot be prepared from commercial β-amino acids or by one-carbon homologation of proteinogenic amino acids. The use of readily available β-hydroxylaminoaldehydes expands the utility of our previously reported method to prepare 2,3-dihydropyridin-4(1H)-ones from β-amino acids as the source of diversity and chirality. A broad substrate scope is possible because β-aminoaldehydes can be prepared from α,β-unsaturated aldehydes by an enantioselective organocatalytic process.

Solid-phase asymmetric synthesis using a polymer-supported chiral Evans'-type oxazolidin-2-one

This protocol describes the synthesis of (S)-4-(4-hydroxybenzyl)-oxazolidin-2-one, its attachment to a Merrifield-Cl resin and its use for asymmetric synthesis. The chiral auxiliary is prepared in four steps from N-Boc-L-tyrosine on a multigram scale in high yield and attached to Merrifield-Cl resin via its phenolic group to afford a solid-supported chiral auxiliary for asymmetric synthesis that takes ∼7 d to prepare. A procedure for its N-acylation is reported and a method for carrying out diastereoselective solid-supported Evans' syn-aldol reactions is described, with aldol products being cleaved from the polymer by either hydrolysis or reduction. The use of the supported auxiliary for two sequential 'on-bead' reactions has been demonstrated for the synthesis of a chiral cyclopropane aldol and a γ-lactone in a >95:5 diastereomeric ratio. These polymer-supported reactions are carried out in IRORI Kan resin capsules to protect the polymer support from mechanical degradation, thus allowing multiple on-bead reactions to be performed.