The synthesis of Dilantin also involves imines (expt 7):. Imines in putative prebiotic synthesis of histidine:. Strecker synthesis. Interestingly, AA’s have been detected in space: Murchison Meteorite: Murchison, Australia (1969)
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i.e., Natural abundance of 15N is 0.37%, however, meteorites were found to have +50% to 93%
There had to be a natural process that separated & concentrated one enantiomer over the other → chiral selection
Mechanism of enrichment?
i.e., one face is exposed to light or one face is immersed (by chance) in water
**Does calcite promote amino acid chain formation?
(Cooks et al,. Angew. Chem. Int. Ed., 2003, 42, 3521)
(Feringa et al,. Chem. Commun., 2007, 2578)
one L-serine selects to bind with 7 more L-enantiomers
Another mechanism for enantioenrichment: concentrated one enantiomer over the other organocatalysisvia the aldol reaction
Cordova, A et al. Chem. Commun.2005, 3586-3588
Mechanism: concentrated one enantiomer over the other
Chirality in the enamine is transferred to the new chiral centres in the aldol
Proposed to occur via a 6-membered TS:
Chirality in the enamine is transferred to the 2 new chiral centres in the aldol
Cordova et al. concentrated one enantiomer over the other Chem. Commun., 2005, 2047-2049
L-proline: a 2° amine; popular as an organocatalyst because it forms enamines readily
Mechanism: enamine formation concentrated one enantiomer over the other
CO2H participates as acid
% ee of sugar vs % ee of AA