1H NMR study of protected and unprotected kainoid amino acids: facile assignment of C-4 stereochemistry

Synthesis of Kainoids and C4 Derivatives

A unified stereoselective synthesis of 4-substituted kainoids is reported. Four kainic acid analogues were obtained in 8-11 steps with up to 54% overall yields. Starting from trans-4-hydroxy-l-proline, the sequence enables a late-stage modification of C4 substituents with sp² nucleophiles. Stereoselective steps include a cerium-promoted nucleophilic addition and a palladium-catalyzed reduction. A 10-step route to acid 21a was also established to enable ready functionalization of the C4 position.

Regio- and Stereoselective Heck Arylations of N-Carbomethoxy-l- 3-Dehydroproline Methyl Ester with Arenediazonium Salts. Total Synthesis of Neuroexcitatory Aryl Kainoids

The Heck arylation of N-carbomethoxy-L-3-dehydroproline methyl ester with arenediazonium tetrafluoroborates produced chiral 4-aryldehydroproline derivatives in moderate to good yields in a highly regio- and stereocontrolled fashion. A rationale for the unexpected high regioselectivity is provided using Deeth's model. Heck adduct 15 (G = o-CH3O) was converted into several aryl kainoids using concise and efficient routes.

Synthesis of a bis-azido analogue of acromelic acid for radioisotope-free photoaffinity labeling and biochemical studies

A novel acromelic acid analogue containing a phenyl group possessing two different types of azido functional groups, of which one is the aromatic N3 acting as a photoaffinity group to bind to a target protein by photoirradiation and the other is alkyl N3 group which survives photolysis acting as a detecting group through the Staudinger-Bertozzi reaction to identify the ligated product, was designed and synthesized as a radioisotope-free biochemical probe potentially for studies on kainoid receptors.

Parallel synthesis of novel heteroaromatic acromelic acid analogues from kainic acid

A range of new C-4 heteroaromatic acromelic acid analogues has been synthesized in a parallel fashion from (-)-alpha-kainic acid 1. Protection of the amine and carboxylate groups of 1 followed by ozonolysis gave methyl ketone 8. A silyl enol ether 9, generated regiospecifically from the methyl ketone 8 using "kinetic" conditions, was brominated in situ with phenyltrimethylammonium perbromide to give the key alpha-bromo ketone 10. Parallel cyclization reactions of bromo ketone 10 with thioamides and thioureas were then performed. The aromatic heterocyclic derivatives 11a-d and 19 produced were deprotected to give the new kainoid amino acids 6a-d and 25 in excellent yield. Compounds 6a and 6c show strong binding to the kainate receptor. Reaction of 10 with alternative condensing agents was also briefly investigated.