Lactic acids, macrocyclic derivatives

The pyridine subcycle unit has been introduced into a wide range of 18-crown-6 derivatives. For example, reaction of 2,6-pyridinedicarbonyl chloride with the dimethyl substituted tetraethylene glycol (SS)-84, derived from (S)-lactic acid, afforded (126) the chiral macrocyclic polyether diester (5S)-184. A similar preparative approach (127) gave (SS)-185, where the source of the chirality is (5)-mandelic acid. 

The 18-membered ring macrocyclic polyether diester (S5)-184 [containing a pyridino subunit and derived from (5)-lactic acid] with both enantiomers [i.e., R) and (S)] of the a-C,oH7CHMeNH3 cation (205). 

Commercially available silica gel plates coated with acid or basic chiral selectors [o-galacturonic acid, l-(- -)-tartaric acid, L-lactic acid, (-)-brucine] were used for the separation of racemic ephedrine, atropine, neutral amino acids, and their 3-phenyl-2-thiohydantoins (PTH) derivatives. The use of amino acids as chiral selectors involved further possibilities of enantiomer separation owing to the simultaneous presence of basic and acidic groups. In fact, L-aspartic acid, L-lysine, L-histidine, L-arginine, and L-ser-ine resolved racemic alkaloids, (3-blockers, profens, some amino acids, and their Dns derivatives. Macrocyclic antibiotics [i.e., (-)-erythromycin and (-)-vancomycin] were also used as chiral agents for the separation of enantiomeric DNs amino acids. The mechanisms of chiral recognition was investigated by Aboul-Enein, El-Awady, and Heard they hypothesized that the formation of... 

In the last two decades, chiral receptors containing amidic functions were designed almost exclusively for binding protected amino acids [49-57], oligopeptides [54,58], and lactic [59], tartaric [60,61] or camphoric acid derivatives [62]. Usually, chiral building blocks such as spirobifluorene [49, 60], binaphthalene [51,57],or amino acid chains containing macrocycles [52-56,58] were employed. An interesting receptor was synthesized via connection of the calix[4]arene moiety with an aza-crown derivative [61]. 

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