60434-72-2Relevant articles and documents
The entrapment of chiral guests with gated baskets: Can a kinetic discrimination of enantiomers be governed through gating-
Wang, Bao-Yu,Stojanovic, Sandra,Turner, Daniel A.,Young, Tanya L.,Hadad, Christopher M.,Badjic, Jovica D.
, p. 4767 - 4775 (2013)
The capacity of gated hosts for controlling a kinetic discrimination between stereoisomers is yet to be understood. To conduct corresponding studies, however, one needs to develop chiral, but modular and gated hosts. Accordingly, we used computational (RI-BP86/TZVP//RI-BP86/SV(P)) and experimental (NMR/CD/UV/Vis spectroscopy) methods to examine the transfer of chirality in gated baskets. We found that placing stereocenters of the same kind at the rim (R1=CH3, so-called bottom) and/or top amide positions (R2=sec-butyl) would direct the helical arrangement of the gates into a P or M propeller-like orientation. With the assistance of 1H NMR spectroscopy, we quantified the intrinsic (thermodynamic) and constrictive (kinetic) binding affinities of (R)- and (S)-1,2-dibromopropane 5 toward baskets (S3b/P)-2, (S3t/M)-3, and (S3bt/P)-4. Interestingly, each basket has a low (≤1.3 kcal mol-1), but comparable (de3b/P)-2, with a set of S stereocenters at the bottom and P arrangement of the gates, would capture (R)-5 at a faster rate (kinR/kinS=2.0±0.2). Basket (S3t/M)-3, with a set of S centers at the top and M arrangement of the gates, however, trapped (S)-5 at a faster rate (kin R/kinS=0.30±0.05). In light of these findings, basket (S3bt/P)-4, with a set of S stereocenters installed at both top and bottom sites along with a P disposition of the gates, was found to have a lower ability to differentiate between enantiomeric (R/S)-5 (k inR/kinS=0.8). Evidently, the two sets of stereocenters in this "hybrid" host acted concurrently, each with the opposite effect on the entrapment kinetics. Gated baskets are hereby established to be a prototype for quantifying the kinetic discrimination of enantiomers through gating and elucidating the electronic/steric effects on the process. Falling into a trap: Controlling the rate at which two stereoisomeric compounds enter a host presents a challenge. Gated molecular baskets (see figure) are shown to be excellent prototypes for implementing a kinetic differentiation of guests. Copyright
Stereochemical control in microbial reduction. 12. (S)-4-nitro-2-butanol as a source to synthesize natural products
Nakamura,Kitayama,Inoue,Ohno
, p. 91 - 96 (2007/10/02)
(S)-(+)-4-Nitro-2-butanol (1) obtained by the stereoselective reduction of 4-nitro-2-butanone by bakers' yeast was employed for the syntheses of natural products. A precursor of (+)-brefeldin A is synthesized starting from this chiral building block by 10 steps short-cut procedure compared with the shortest method so far reported. (S)-(+)-Sulcatol is obtained in much better enantiomeric purity than those reported. The reactivity of 1 in base-catalyzed condensations with Michael acceptors or aldehydes is largely affected by a base employed as the catalyst.
