A method for preparing organic products from aqueous solutions, such as waste or byproduct liquid streams and waste or byproduct gas or vapor streams, uses phase transfer catalysis to transfer a chemical species in low concentration from the aqueous solution to the organic phase or the aqueous-organic interface. The system has little or no organic solvent, and the organic phase contains an electrophile which participates in the reaction. In one embodiment, the aqueous solution is contacted with the electrophile and a phase transfer catalyst and, optionally, a pH adjusting agent in the event that the chemical species in the aqueous solution is not sufficiently ionized to react with the electrophile, and optionally an organic solvent. A method for continuously converting a chemical species involves this contacting step, separating the phases, then dividing the organic phase into the product, the phase transfer catalyst, and the optional organic solvent.

One aspect of the present invention relates to methods of asymmetric synthesis, e.g., asymmetric hydride reductions of carbonyl groups, using a chiral, non-racemic phase transfer catalyst, a helper nucleophile, and a sterically bulky reagent nucleophile, e.g., an alkoxyhydride derived from a sacrificial ketone and a hydride reagent. Moreover, the sterically bulky reagent nucleophile may be generated in situ or prepared in a prior step. Another aspect of the present invention relates to chiral non-racemic phase transfer catalysts, and their use in the subject methods.

Non-natural amino acids such as 2-alkylated amino acids allow for the synthesis of a wider variety of peptidal and non-peptidal pharmaceutically active agents. In one embodiment, the present invention relates to a method of preparing 2-alkylcysteine comprising condensing cysteine with an aryl nitrile to form a 2-arylthiazoline-4-carboxylic acid, forming a 2-arylthiazoline-4-amide using an amine group comprising at least one substituted or unsubstituted alkyl group that comprises one or more chiral carbon atoms, and alkylating at the 4-position of the thiazoline ring to form a 2-aryl-4-alkyl-thiazoline-4-amide. The present invention also discloses a method of preparing a class of iron chelating agents related to desferrithiocin, all of which contain a thiazoline ring. In one embodiment, an aryl nitrile or imidate is condensed with cysteine or a 2-alkyl cysteine.

A useful and efficient method of preparing an alkylated thiazoline carboxylic acid, or a derivative thereof, comprises coupling a substituted aryl nitrile such as, for example, 2,4-dimethoxybenzonitrile or 4-methoxybenzonitrile, with a cysteine ester to form a substituted thiazoline carboxylic acid ester; optionally hydrolyzing the substituted thiazoline carboxylic acid ester to form a substituted thiazoline carboxylic acid; optionally, protecting the carboxyl group; alkylating the thiazoline ring at the 4-carbon position, as indicated in Structural Formula (I), with a compound of the formula R.sub.1-L, wherein R.sub.1 is as defined above and L is a leaving group, in the presence of a phase transfer catalyst; and, optionally, deprotecting the carboxyl group.In one embodiment of the present invention, a cinchona-alkaloid derived phase transfer catalyst is used to alkylate a protected substituted thiazoline carboxylic acid.

Non-natural amino acids such as 2-alkylated amino acids allow for the synthesis of a wider variety of peptidal and non-peptidal pharmaceutically active agents. In one embodiment, the present invention provides methods of preparing 2-alkylcysteine derivatives. In another embodiment, the method comprises forming a 2-alkylcysteine derivative from a cysteine derivative in the presence of a phase transfer catalyst. In particular, the present invention provides methods for preparing 2-methylcysteine derivatives.The present invention also discloses a method of preparing a class of iron chelating agents related to desferrithiocin, all of which contain a thiazoline ring. In one aspect, an aryl nitrile or imidate is condensed with cysteine or a 2-alkyl cysteine. The present invention also relates to the preparation of 4,5-dihydro-2-(2,4-dihydroxyphenyl)-4-alkyl-thiazole-4-carboxylic acids, such as 4,5-dihydro-2-(2,4-dihydroxyphenyl)-4-methyl-thiazole-4-carboxyli- c acid.