Strecker synthesis has long been considered one of the prebiotic reactions for the synthesis of α-amino acids. However, the correlation between the origin of chirality and highly enantioenriched α-amino acids through this method remains a puzzle. In the reaction, it may be conceivable that the handedness of amino acids has been determined at the formation stage of the chiral intermediate α-aminonitrile, that is, the enantioselective addition of hydrogen cyanide to an imine. Herein, an enantiotopic crystal surface of an achiral imine acted as an origin of chirality for the enantioselective formation of α-aminonitriles by the addition of HCN. In conjunction with the amplification of the enantiomeric excess and multiplication of enantioenriched aminonitrile, a large amount of near enantiopure α-amino acids, with the l- and d-handedness corresponding to the molecular orientation of the imine, is reported.
An efficient synthesis of a doubly stranded [3]rotaxane has been developed through bridging of a pseudo[3]rotaxane featuring two axle components. Reversible azine formation was effective as the bridging reaction. Kinetic and thermodynamic conditions provided the [2]- and [3]rotaxanes, respectively.
Under aqueous conditions, total spontaneous resolution of α-aminonitrile occurred by the reaction of three achiral reagents; therefore, absolute asymmetric Strecker synthesis was demonstrated.
The volatile odor-active compounds
of cooked rice were evaluated
using a method that combined solid-phase microextraction (SPME) with
gas chromatography–resonance-enhanced multiphoton ionization
time-of-flight mass spectrometry (GC/REMPI-TOFMS). An SPME fiber was
held at the upper levels of the cooked rice and given an extraction
time of 5 min. By using a nanosecond ultraviolet (266 nm) pulsed laser
for ionization, two compounds, 4-vinylphenol and indole, which are
considered to be important for the characteristic flavor of cooked
rice, could be detected from all types of cultivars measured in the
present study—nonglutinous rice, glutinous rice, and aromatic
rice. In the case of fresh nonglutinous rice, the amounts of introduction
for 4-vinylphenol and indole to GC were ca. 70 and 20 pg, respectively.
While both peak areas decreased with increases in the time needed
to maintain warmth, the decreasing behaviors differed slightly with
a noteworthy rapid decrease for indole. For nonglutinous rice, the
peak areas for 4-vinylphenol were almost the same, whether it was
fresh (measured within 1 month from harvest) or aged (measured 6–12
months after harvest), but those of indole significantly decreased
following storage. We also found differences among cultivars: the
peak area for 4-vinylphenol in nonglutinous rice was somewhat strong;
the peak area for indole was intensely strong in glutinous rice; however,
the peak areas for both 4-vinylphenol and indole were weak in aromatic
rice. Volatile odor-active compounds were detected in a sensitive
and time-resolved manner; therefore, the proposed method could be
useful for differentiating varieties of cooked rice from the viewpoints
of cooking conditions, freshness, and cultivar types.
A helically chiral [2]rotaxane featuring two ammonium ion recognition sites in the dumbbell-like component and a calix-bis-crown ether as the macrocyclic component was synthesized, but with no chirality in either individual component. The enantiomeric nature of the isomers, separated through chiral HPLC, was apparent in their CD spectra, which were mirror images for all wavelengths.
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