Synthetic studies of the HIV-1 protease inhibitive didemnaketals: precise and stereocontrolled synthesis of the key mother spiroketal

The precise and stereocontrolled synthesis of the C₉-C₂₃ portion, the key mother spiroketal of the HIV-1 protease inhibitive didemnaketals from the ascidian Didemnum sp., has been carried out through multisteps starting from (R)-pulegone as the chiral template. This approach involved the distereoselective construction of eight chiral centers by intramolecular chiral inducement and the coupling of two fragments by Julia reaction.     

Stereoselective total synthesis of almorexant

A highly stereoselective synthesis of almorexant has been achieved using (R)-tert-butanesulfinamide as a chiral source. The chiral tetrahydroisoquinoline core was constructed through allylation of chiral N-sulfinyl imine followed by ring closure of the secondary amide with a tethered halide. The chiral α-phenyl amide was introduced by means of S_N2 substitution of (S)-methyl 2-phenyl-2-(tosyloxy)acetate with chiral tetrahydroisoquinoline.     

Synthetic studies of the HIV-1 protease inhibitive didemnaketals: stereocontrolled synthesis of an ester side chain

The stereocontrolled synthesis of the C₁-C₈ portion, the ester side chain of the HIV-1 protease inhibitive didemnaketals from the ascidian Didemnum sp., has been carried out through 15 steps starting from (S)-carvone as the chiral template. This approach involved the diastereoselective construction of three conjoint chiral centers by intramolecular chiral inducement, and generation of allylic alcohol intermediate through a key Grob fragmentation reaction.     

Study on selectivity of permeating chiral complexes in bilayer lipid membranes (BLMs)

Electrical properties such as membrane potential (E_m) of planar bilayer lipid membranes (BLMs) are readily measured. Planar BLMs have been extensively used as models of biomembranes. In this paper we report BLMs formed in the solutions containing chiral complexes: d-K[Co(EDTA)], l-K[Co(EDTA)]; d-[Co(C₂O₄)(en)₂]I, and l-[Co(C₂O₄)(en)₂]I, whose E_m values display great differences, implying strong chiral selectivity. The permeability ratios of different chiral complexes calculated from E_m are the same as those obtained from human erythrocyte experiments. These results showed that chiral selectivity of cell uptake was mainly caused by the chirality of the membrane phospholipid itself. As a rapid and sensitive analytic tool, the BLM may be used to study permeating pathways and drug–membrane interactions. With further research, the BLM system may be developed into a useful method for drug screening.     

New chiral polyfunctional cyclobutane derivatives from (−)-verbenone: possible surfactant behaviour

New enantiopure cyclobutane derivatives have been synthesized from a chiral precursor derived from (?)-verbenone. The cyclobutane moiety acts as a chiral platform to afford a γ-amino acid function in a branched side-chain containing an additional stereogenic centre as well as additional C₆ or C₁₆-alkyl chains linked to the ring by means of an amine or an amide function. One of these compounds, obtained as a 1:2 mixture with its TFA salt has been investigated, suggesting behaviour as a good surfactant and its critical micellar concentration has been determined.     

Chiral solvating agents for carboxylic acids based on the salen moiety

A series of chiral salen C₂-symmetric aminophenols 1–4, which were derived from (1R,2R)- or (1S,2S)-1,2-diphenylethane-1,2-diamine with the corresponding salicylic aldehyde through a [2+2] condensation reaction, have been prepared. The NMR studies demonstrated that they can function as chiral solvating agents for the determination of the enantiomeric purity of chiral carboxylic acids.     

Chiral N-phosphonyl imine chemistry: new reagents and their applications for asymmetric reactions

Novel chiral N-phosphonyl imines 2 have been designed and synthesized using chiral N-phosphoramide 1. These N-phosphonyl imines have been successfully utilized for asymmetric aza-Darzens reaction and asymmetric aza-Henry reaction. The C₂-symmetric chiral auxiliary tolerates oxidation, is not sensitive to racemization and can be recycled for large scale synthesis.     

Template effects on the asymmetric cycloaddition reaction between 3,4-dimethyl-1-phenylarsole and diphenylvinylphosphine and their arsenic elimination reaction

The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]naphthalene as the chiral template was employed to promote the asymmetric cycloaddition reaction between 3,4-dimethyl-1-phenylarsole and diphenylvinylphosphine. It has been proven that the chiral template incorporating napthylamine is more efficient than the benzylamine based analogue as evidenced by the drastic improvement in stereoselectivity and reaction rate. However, when no chiral template was employed, trans-[PdI₂(3,4-dimethyl-1-phenylarsole)₂] reacted with trans-[PdI₂(diphenylvinylphosphine)₂] producing a structurally novel diiodo complex, as a result of an interesting selective cleavage of one As-C bond in the norbornene skeleton and subsequent rearrangements within the skeletal framework. The molecular structure of the diiodo product has been confirmed by X-ray crystallography. Structural analysis showed that in addition to the normal As-P five-membered ring, there is one new five-membered ring containing As-O bond being formed during the course of the reaction along with another seven-membered ring incorporating a hydroxy group.     

Synthesis of C1-symmetric chiral tripodal oxazolines through an oxazoline exchange reaction with amino alcohols

Various C₁-symmetric chiral tripodal tris(oxazolines) with two different oxazoline units were synthesized from chiral C₃-symmetric tris(oxazolines) through an oxazoline exchange reaction with amino alcohols in the presence of zinc chloride. Evaluation of the new oxazolines as chiral molecular receptor showed that some of the receptors have chiral discrimination ability.     

An enantiopure galactose oxidase model: synthesis of chiral amino alcohols through oxidative kinetic resolution catalyzed by a chiral copper complex

An enantiopure galactose oxidase (GO) enzyme model has been synthesized from readily available (R)-BINAM and Cu(OTf)₂, and the enantiopure GO model has been effectively used in situ as an efficient chiral catalyst for the synthesis of chiral amino alcohols through oxidative kinetic resolution (OKR), where molecular oxygen is used as the sole oxidant. Under the proposed catalytic conditions, both ortho- and para-substituted amino alcohols were resolved with good to excellent enantiomeric excesses through oxidative kinetic resolution.     

Asymmetric synthesis of substituted 1-aminocyclopropane-1-carboxylic acids from a new chiral glycine equivalent with 3,6-dihydro-2H-1,4-oxazin-2-one structure

Condensation of the new chiral glycine equivalent 10 with aldehydes at room temperature in the presence of K₂CO₃ under solid–liquid phase-transfer-catalysed conditions afforded stereoselectively new chiral (Z)-α,β-didehydroamino acid (DDAA) derivatives with oxazinone structure 14. These systems have been used in diastereoselective cyclopropanation reactions for the synthesis of enantiomerically pure 1-aminocyclopropanecarboxylic acids (ACCs) such as (−)-allo-norcoronamic and (−)-allo-coronamic acids.     

Enantioselective sensing of lactate by pyridinium-based chiral receptor

A simple pyridinium-based chiral receptor 1 containing l-valine as the chiral source has been designed and synthesized. The receptor 1 fluorometrically recognizes d-lactate over l-lactate in CH₃CN with an enantiomeric fluorescence ratio (ef) of 5.32.     

Chiral calix[4]azacrowns for enantiomeric recognition of amino acid derivatives

In this study the synthesis of novel chiral calix[4]azacrown derivatives has been reported. The enantioselectivity of chiral receptors was investigated by using UV-vis spectroscopy. All the chiral calix[4]arene derivatives exhibited certain chiral recognition toward the enantiomers of phenylalanine (Phe-OMe·HCl) and alanine methyl ester hydrochlorides (Ala-OMe·HCl). As a chiral receptor, the furfuryl-armed calix[4]azacrown ether 7 has the best enantiomeric discriminating ability for α-amino acid ester hydrochlorides (up to K_L/K_D=2.08, ΔΔG₀=−1.82 kJ mol⁻¹) in CHCl₃. The enantiomeric recognition abilities for guests are also discussed from a thermodynamic point of view.     

Synthesis of C2-symmetrical chiral diamines: diastereoselective addition to bis(1,3-oxazolidinyl)alkanes with Grignard reagents

Asymmetric syntheses of C₂-symmetrical chiral 1,4- and 1,5-diamines with stereogenic centers adjacent to the nitrogen atom have been accomplished. Chiral diamines were prepared by diastereoselective alkylations of bisoxazolidine, which was derived from (R)-phenylglycinol. Methyl and phenyl Grignard reagents were employed as alkylating reagents. In addition, tertiary chiral diamines were readily converted to primary diamines in high yield.     

Synthesis of enantiomerically pure telluronium salts by the reaction of chiral tellurides with alkyl halides

Enantiomerically pure benzyl and ethoxycarbonylmethyl telluronium salts 4, using 2-exo-hydroxy-10-bornyl group as a chiral ligand, have been prepared in good yield and diastereoselectivity by the reaction of chiral tellurides 3 with alkyl halides. A structure with R_Te absolute configuration at the tellurium atom was confirmed by an X-ray analysis of 4a.     

A new approach to enantioselective cyanation of imines with Et2AlCN

An enantioselective Strecker-type reaction of imines with Et₂AlCN in the presence of chiral additives has been examined. The enantioselectivity varied depending on the substituents of the imino group as well as the chiral additives used. Thus, α-aminonitriles were obtained in good yields with good enantioselectivities in the reaction of N-benzylidenebenzhydrylamine with Et₂AlCN and BINOL. The reaction with excess BINOL gave the aminonitrile with reversed configuration.     

Asymmetric addition of phenylacetylene to aldehydes catalyzed by soluble optically active polybinaphthols ligand

A chiral polymer ligand was synthesized by the polymerization of (S)-5,5′-dibromo-6,6′-dibutyl-2,2′-binaphthol (S-M-1) with (S)-2,2′-bishexyloxy-1,1′-binaphthyl-6,6′-boronic acid (S-M-2) via Pd-catalyzed Suzuki reaction. The application of the chiral polymer ligand to the asymmetric addition of phenylethynyl zinc to various aldehydes has been studied. The results show that the soluble chiral polybinaphthols ligand in combination with Et₂Zn and Ti(OⁱPr)₄ can exhibit excellent enantioselectivity for phenylacetylene addition to both aromatic and aliphatic aldehydes. The catalytically active center of the repeating unit S-1 used as a catalyst produced the opposite configuration of the propargylic alcohols to that of S-1, on the contrary, the chiral polymer gave the same configuration as the optically active binaphthol moiety of the polybinaphthols ligand. Moreover, the chiral polymer ligand can be easily recovered and reused without loss of catalytic activity as well as enantioselectivity.     

New C2-symmetric chiral phosphinite ligands based on amino alcohol scaffolds and their use in the ruthenium-catalysed asymmetric transfer hydrogenation of aromatic ketones

Asymmetric transfer hydrogenation processes of ketones with chiral molecular catalysts are attracting increasing interest from synthetic chemists due to their operational simplicity. C₂-symmetric catalysts have also received much attention and been used in many reactions. A series of new chiral C₂-symmetric bis(phosphinite) ligands has been prepared from corresponding amino acid derivated amino alcohols or (R)-2-amino-1-butanol through a three- or four-step procedure. Their structures have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis. ¹H-³¹P NMR, DEPT, ¹H-¹³C HETCOR or ¹H-¹H COSY correlation experiments were used to confirm the spectral assignments. In situ prepared ruthenium catalytic systems were successfully applied to ruthenium-catalyzed asymmetric transfer hydrogenation of acetophenone derivatives by iso-PrOH. Under optimized conditions, these chiral ruthenium catalyst systems serve as catalyst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in iso-PrOH and act as good catalysts, giving the corresponding optical secondary alcohols in 99% yield and up to 79% ee.     

Manganese catalyzed asymmetric transfer hydrogenation of ketones

The asymmetric transfer hydrogenation (ATH) of a wide range of ketones catalyzed by manganese complex as well as chiral P_xN_y-type ligand under mild conditions was investigated. Using 2-propanol as hydrogen source, various ketones could be enantioselectively hydrogenated by combining cheap, readily available [MnBr(CO)₅] with chiral, 22-membered macrocyclic ligand (R,R,R',R')-CyP₂N₄ (L5) with 2 mol% of catalyst loading, affording highly valuable chiral alcohols with up to 95% ee.     

Chiral eighteen-component three-dimensional supramolecular entities stabilized by the hydrogen bonding and coordination interactions

A new class of chiral eighteen-component three-dimensional supramolecular entities has been assembled in toluene and chloroform from twelve zinc porphyrin-appended 2-(ethylamino)- pyrimido[4,5-b][1,8]naphthyridin-4(3H)-one monomers and six chiral bipyridyl compounds. The heterocyclic segments form two C₆-symmetric cyclic hexamers, which are stabilized by a well-established DDA-AAD hydrogen bonding motif, while the six chiral bispyridine ligands are coordinated to the corresponding zinc porphyrin units to give the two-layered architectures. The structures have been characterized by the ¹H NMR, UV-vis and circular dichroism experiments, which also reveals that, when the concentration of the monomers is high enough, the chiral supramolecular entity can be formed exclusively.