Synthesis and optical resolution of 2-aryl-2-fluoropropionic acids, fluorinated analogues of non-steroidal anti-inflammatory drugs (NSAIDs)

We report the synthesis of optically active 2-aryl-2-fluoropropionic acids 2 as non-epimerizable mimics of 2-arylpropionic acids 1, a class of compounds which have been widely used as non-steroidal anti-inflammatory drugs (NSAIDs). This is a continuation of our research involving the design, synthesis, and evaluation of chiral fluorine-containing organic molecules as effective analogues of pharmacologically important compounds.     

Synthesis of functionalized asymmetric star polymers containing conductive polyacetylene segments by living anionic polymerization

Novel 3-arm ABC, 4-arm ABCD, and 5-arm ABCDE asymmetric star polymers comprising the conductive polyacetylene precursor, poly(4-methylphenyl vinyl sulfoxide) (PMePVSO), and other segments, such as polystyrene, poly(alpha-methylstyrene), poly(4-methoxystyrene), poly(4-trimethylsilylstyrene), and poly(4-methylstyrene), were synthesized by the methodology based on living anionic polymerization using DPE-functionalized polymers. This methodology involves the addition reaction of a DPE-functionalized polymer to a living anionic polymer followed by the living anionic polymerization of MePVSO initiated from the in situ formed polymer anion with two, three, or four polymer segments. The resultant asymmetric star polymers possessed predetermined molecular weights, narrow molecular weight distributions (Mw/Mn < 1.03), and desired compositions as confirmed by SEC, 1H NMR, SLS, and elemental analysis. After thermal treatment, the PMePVSO segment in the star polymer could be completely converted into a conductive polyacetylene segment, evident from TGA and elemental analysis. These asymmetric star polymers are expected to exhibit interesting solution properties and unique microphase-separated morphological suprastructures with potential applications in nanoscopic conductive materials. Moreover, this methodology can afford the target asymmetric star polymers with arm segments varying in a wide range and enables the synthesis of more complex macromolecular architectures.     

Analysis of Digital Lateral Shearing Interferometer

A new method is proposed for reconstructing wavefront from discretely sampled interferogram data obtained by a digital lateral shearing interferometer. Assumptions applied in the conventional methods are not used and reconstruction error caused by the difference between the amount of shear and the sampling interval can be removed. System error and the influence of the discrete sampling, which limit accuracy of the tested results of the lateral shearing interferometer, are analyzed.     

Complexability of o-bisguanidinobenzenes with arsenic and phosphoric acids in solution and solid states, and the potential use of their immobilized derivatives as solid base ligands for metal salts and arsenic acid

The role of o-bisguanidinobenzenes (BGBs) as new Brønsted base ligands for arsenic and phosphoric acids was examined. In solution state, complexation was evaluated by Job’s plot in ¹H NMR experiment, indicating a 1:1 complex formation, whereas in solid state crystalline structures of complexes obtained were addressed by X-ray crystallographic analysis and/or solid state ¹³C NMR experiment, in which 1:2 complexes between the BGB and the acid components were normally formed. Based on these results, Merrifield and Hypogel^® resin-anchored BGBs were designed and prepared as the corresponding polymer-supported host ligands. Evaluation of their coordination ability with metal salts (ZnCl₂ and CoCl₂) and arsenic acid in aqueous media by ICP-MS showed that the latter Hypogel^® resin-anchored BGBs acted as effective immobilized base ligands.     

The Stein phenomenon for monotone incomplete multivariate normal data

We establish the Stein phenomenon in the context of two-step, monotone incomplete data drawn from , a (p+q)-dimensional multivariate normal population with mean and covariance matrix . On the basis of data consisting of n observations on all p+q characteristics and an additional N−n observations on the last q characteristics, where all observations are mutually independent, denote by the maximum likelihood estimator of . We establish criteria which imply that shrinkage estimators of James-Stein type have lower risk than under Euclidean quadratic loss. Further, we show that the corresponding positive-part estimators have lower risk than their unrestricted counterparts, thereby rendering the latter estimators inadmissible. We derive results for the case in which is block-diagonal, the loss function is quadratic and non-spherical, and the shrinkage estimator is constructed by means of a nondecreasing, differentiable function of a quadratic form in . For the problem of shrinking to a vector whose components have a common value constructed from the data, we derive improved shrinkage estimators and again determine conditions under which the positive-part analogs have lower risk than their unrestricted counterparts.     

Epoc group: transformable protecting group with gold(iii)-catalyzed fluorene formation

This study presents the novel concept of a transformable protecting group, which changes its properties through structural transformation. Based on this concept, we developed a 2-(2-ethynylphenyl)-2-(5-methylfuran-2-yl)-ethoxycarbonyl (Epoc) group. The Epoc group was transformed into an Fmoc-like structure with gold(iii)-catalyzed fluorene formation and was removable under Fmoc-like mild basic conditions post-transformation even though it was originally stable under strongly basic conditions. As an application for organic synthesis, the Epoc group provides the novel orthogonality of gold(iii)-labile protecting groups in solid-phase peptide synthesis. In addition, the high turnover number of fluorene formation in aqueous media is suggestive of the applicability of the Epoc group to biological systems.

A protecting group removable with gold(iii)-catalyzed fluorene formation and the subsequent addition of piperidine was developed.     

Chemo- and stereoselective six-membered oxonium ylide formation–[2,3]-sigmatropic rearrangement of 2-diazo-3-ketoesters with dirhodium(II) catalyst and its application to the synthesis of (+)-tanikolide

Dirhodium(II)-catalyzed oxonium ylide formation–[2,3]-sigmatropic rearrangement of 6-allyloxy-2-diazo-3-ketoesters possessing a C-6 substituent is described. The reaction of 6-alkyl- or 6-aryl-substituted 6-allyloxy-2-diazo-3-ketoesters with a catalytic amount of Rh₂(S-PTTL)₄ proceeded in a chemoselective and stereoselective manner to provide 6-substituted 2-allyl-3-oxotetrahydropyran-2-carboxylates in good yields and with high diastereoselectivities. To demonstrate the utility of this sequential reaction, we conducted the total synthesis of (+)-tanikolide, in which the construction of the δ-lactone skeleton was achieved by employing a 2-iodobenzamide-catalyzed oxidative cleavage of tetrahydropyran-2-methanol.     

Discrete π Stack of a Tweezer-Shaped Naphthalenediimide–Anthracene Conjugate

The design and synthesis of a tweezer-shaped naphthalenediimide (NDI)–anthracene conjugate ( 2NDI ) are reported. In the structure of the closed form (π_NDI ⋅⋅⋅ π_NDI stack) of 2NDI , which was elucidated by single-crystal XRD, the existence of C−H ⋅⋅⋅ O hydrogen bonding involving the nearest carbonyl oxygen atom of an NDI unit was suggested. The tunability of π_NDI ⋅⋅⋅ π_NDI interactions was studied by means of UV/Vis absorption, fluorescence and NMR spectroscopy and molecular modelling. This revealed that the π_NDI ⋅⋅⋅ π_NDI interactions in 2NDI affect the absorption and emission properties depending on the temperature. Furthermore, in polar solvents, 2NDI prefers the stronger π_NDI ⋅⋅⋅ π_NDI stack, whereas the π_NDI ⋅⋅⋅ π_NDI interaction is diminished in nonpolar solvents. Importantly, the conformational variations of 2NDI can be reversibly switched by variation in temperature, and this suggests potential application for fluorogenic molecular switches upon temperature changes.