Total Synthesis of (+)-Hygrine via Asymmetric Phase-Transfer Catalytic Alkylation

The first enantioselective synthesis of (+)-hygrine (1) is reported. 1 was obtained in 12 steps with 29% overall yield and 97% ee via asymmetric phase-transfer catalytic alkylation and ring-closing metathesis as key steps. The absolute configuration of (+)-hygrine could be directly confirmed as R

Evidence of the Electronic Factor for the Highly Enantioselective Catalytic Efficiency of <i>Cinchona</i>-Derived Phase-Transfer Catalysts

The Cinchona alkaloid-derived quaternary ammonium salts containing 2‘-N-oxypyridine and 2‘-cyanobenzene moieties were prepared and evaluated as phase-transfer catalysts in the enantioselective alkylation of glycine imine ester 1. The N-oxypyridine and cyanobenzene moieties might play an important role to form a rigid conformation by coordinating with H2O via hydrogen bonding leading to high enantioselectivity (97∼>99% ee), which provides evidence of an electronic factor for the high enantioselective catalytic efficiency in phase-transfer alkylation

Total Synthesis of (+)-Hygrine via Asymmetric Phase-Transfer Catalytic Alkylation

The first enantioselective synthesis of (+)-hygrine (1) is reported. 1 was obtained in 12 steps with 29% overall yield and 97% ee via asymmetric phase-transfer catalytic alkylation and ring-closing metathesis as key steps. The absolute configuration of (+)-hygrine could be directly confirmed as R

Exposure conditions of different modes in the CS9300 (Carestream Dental LLC, Atlanta, Georgia) and RAYSCAN α+ (Ray Co. Ltd, Hwaseong-si, Korea).

Exposure conditions of different modes in the CS9300 (Carestream Dental LLC, Atlanta, Georgia) and RAYSCAN α+ (Ray Co. Ltd, Hwaseong-si, Korea).</p

Mean and standard deviation of dose-area-product (DAP) values measured with a DAP meter (mGy•cm²) for cone-beam computed tomography with different modes and devices.

Mean and standard deviation of dose-area-product (DAP) values measured with a DAP meter (mGy•cm2) for cone-beam computed tomography with different modes and devices.</p

Dose-area-product (DAP) meter (VacuDAP™; VacuTec Meßtechnik GmbH, Dresden, Germany) for input dose measurement.

An ion chamber was attached on the surface of the X-ray tube head for the measurements.</p

Experimental setting and facilitation for optically stimulated luminescence dosimeter (OSLD) measurements.

(a) OSLD encased in a holder preventing light exposure. There is identification quick response (QR) code and identification number marked on the case. (b) Human tissue-equivalent phantom with dosimeter slots. (c) Dosimetry reader (MicroStar; Landauer) optimized for 80 kVp and a low dose (<30 mGy). Each dosimeter is identified with a QR code and can be read out.</p

The location of optically stimulated luminescent dosimeters (OSLD) in an adult head and neck phantom (ATOM; CIRS, Norfolk, VA, USA) with the slice number of the phantom.

The location of optically stimulated luminescent dosimeters (OSLD) in an adult head and neck phantom (ATOM; CIRS, Norfolk, VA, USA) with the slice number of the phantom.</p

Highly Enantioselective Synthesis of (2<i>S</i>)-α-(Hydroxymethyl)-glutamic Acid by the Catalytic Michael Addition of 2-Naphthalen-1-yl-2-oxazoline-4-carboxylic Acid <i>tert</i><i>-</i>Butyl Ester

Highly enantioselective synthesis of a potent metabotropic receptor ligand, (2S)-α-(hydroxymethyl)-glutamic acid (2, HMG) was accomplished by the catalytic Michael addition of 2-naphthalen-1-yl-2-oxazoline-4-carboxylic acid tert-butyl ester (3b), using the phosphazene base, BEMP, in CH2Cl2 at −60 °C in the presence of (S)-binaphthyl quaternary ammonium salt 4

The effective dose obtained with the OSLD and MC methods, and the percent difference.

The effective dose obtained with the OSLD and MC methods, and the percent difference.</p