Hyun Joon Ha

Dihydroxylation of 2-vinylaziridine: efficient synthesis of D-ribo-phytosphingosine

An efficient and highly stereoselective synthesis of D-ribo-(2S,3S,4R)-phytosphingosine was accomplished in 62% overall yield starting from commercially available (2S)-hydroxymethylaziridine via osmium-catalyzed asymmetric dihydroxylation as a key step.

A simple Cu-64 production and its application of Cu-64 ATSM.

One of the positron emission radionuclides, (64)Cu, has been reported to be a particularly effective radioisotope in PET imaging study. This utility of (64)Cu depends on the chemical stability in water with proper energy and half-life as gamma-emitters. Hence, we tried to develop a simple method for producing this isotope using an old cyclotron model in our site (50MeV, Scantronics co.). In particular, we designed the equipments of enrich (64)Ni plating system and radioactive (64)Cu separation using plastic cartridge column; (64)Ni plating system on gold foil which located in the 13 degrees angle target toward beam irradiation. For the nuclear reaction of (64)Cu, it was applied to (64)Ni(p, n) (64)Cu at low energy under the degrader composed of Al and Ta foils. After beam irradiation, (64)Cu was identified by multichannel analyzer installed for a HPGe detector and its utility was certified by the microPET images of (64)Cu-ATSM (CT-26 tumor bearing mouse as reported previously). The image quality of (64)Cu was also very similar to that of (18)F radioisotope in microPET scanner. In conclusion, a method of (64)Cu production and its application was successfully established in old cyclotron having high energy.

Molecular Basis for the Stereoselective Ammoniolysis of N-Alkyl Aziridine-2-Carboxylates Catalyzed by Candida antarctica Lipase B

Candida antarctica lipase B catalyzed the stereoselective ammoniolysis of N‐alkyl aziridine‐2‐carboxylates in tBuOH saturated with ammonia and yielded the (2S)‐aziridine‐2‐carboxamide and unreacted (2R)‐aziridine‐2‐carboxylate. Varying the N‐1 substituent on the aziridine ring changed the rate and stereoselectivity of the reaction. Substrates with a benzyl substituent or a (1′R)‐1‐phenylethyl substituent reacted approximately ten times faster than substrates with a (1′S)‐1‐phenylethyl substituent. Substrates with a benzyl substituent showed little stereoselectivity (E=5–7) while substrates with either a (1′R)‐ or (1′S)‐1‐phenylethyl substituent showed high stereoselectivity (D>50). Molecular modeling by using the current paradigm for enantioselectivity—binding of the slow enantiomer by an exchange‐of‐substituents orientation—could not account for the experimental results. However, modeling an umbrella‐like‐inversion orientation for the slow enantiomer could account for the experimental results. Steric hindrance between the methyl in the (1′S)‐1‐phenylethyl substituent and Thr138 and Ile189 in the acyl‐binding site likely accounts for the slow reaction. Enantioselectivity likely stems from an unfavorable interaction of the methine hydrogen with Thr40 for the slow enantiomer and from subtle differences in the orientations of the other three substituents. This success in rationalizing the enantioselectivity supports the notion that an umbrella‐like‐inversion orientation can contribute to enantioselectivity in lipases.