A method for esterification of one or more carboxylic acid groups in a compound containing one or more carboxylic acid groups wherein the esterification reagent is a diazo-compound of formula:

##STR00001##

wherein the R.sub.1 and R.sub.2 groups of the diazo compound are selected such that the corresponding organic compound of formula:

##STR00002##

exhibits a —C—H pKa value between 18 and 29 as measured in DMSO. Specific reagents and methods for esterification are provided. The esterification reagents provided exhibit high selectivity for esterification of carboxylic acid groups over reaction with amine, alcohol or thiol groups in the compound containing one or more carboxylic acid groups. The method can be used to selectively esterify carboxylic acid groups in peptides or proteins.

A method for producing an amide includes: subjecting carboxylic acids to dehydration condensation or causing a reaction between a carboxylic acid and a haloformic acid ester; and subsequently causing a reaction with a first base and a reaction with an amine to obtain an amide, wherein the reaction with a first base and/or the reaction with an amine is performed by adding an acid thereto.

A method for producing an amide includes: subjecting carboxylic acids to dehydration condensation or causing a reaction between a carboxylic acid and a haloformic acid ester; and subsequently causing a reaction with a first base and a reaction with an amine to obtain an amide, wherein the reaction with a first base and/or the reaction with an amine is performed by adding an acid thereto.

Disclosed is a method for synthesizing a sitagliptin intermediate, the method comprising: in the presence of hydrogen and a transition metal catalyst having a chiral phosphine ligand, subjecting a compound of formula II to an asymmetric reductive amination with ammonia or ammonium salt in a proper organic solvent under the condition of adding an acidic additive to produce a compound of formula I, wherein, an R- or S-configuration of a stereocenter is represented by *; the compound of formula I of R configuration can be used to prepare sitagliptin, and a reaction formula is as follows: R.sup.1 and R.sup.2 are each independently selected from hydrogen, C.sub.1-C.sub.12 linear or branched alkyl, C.sub.3-C.sub.12 cycloalkyl, C.sub.2-C.sub.12 alkenyl, C.sub.2-C.sub.12 alkynyl and C.sub.7-C.sub.12 arylalkyl. The method has a high yield and a high ee % value, a mild reaction condition and a low production cost, and is simple to operate, convenient to purify, environmental friendly and suitable for industrial production.

##STR00001##

The present disclosure is directed synthetic methods for the preparation of 4-valyloxybutyric acid. The synthetic methods described herein employ a diverse array of protecting group strategies and reaction conditions. Additionally, the present disclosure is directed to compounds useful as synthetic intermediates in the preparation of 4-valyloxybutyric acid.

The present disclosure is directed synthetic methods for the preparation of 4-valyloxybutyric acid. The synthetic methods described herein employ a diverse array of protecting group strategies and reaction conditions. Additionally, the present disclosure is directed to compounds useful as synthetic intermediates in the preparation of 4-valyloxybutyric acid.

This invention provides compositions and methods for producing translational components that expand the number of genetically encoded amino acids in eukaryotic cells. The components include orthogonal tRNAs, orthogonal aminoacyl-tRNA synthetases, orthogonal pairs of tRNAs/synthetases and unnatural amino acids. Proteins and methods of producing proteins with unnatural amino acids in eukaryotic cells are also provided.

This invention provides compositions and methods for producing translational components that expand the number of genetically encoded amino acids in eukaryotic cells. The components include orthogonal tRNAs, orthogonal aminoacyl-tRNA synthetases, orthogonal pairs of tRNAs/synthetases and unnatural amino acids. Proteins and methods of producing proteins with unnatural amino acids in eukaryotic cells are also provided.

The present invention is directed to a new class of lipids, more specifically ether-lipids having a polar headgroup, as well as vesicles comprising these lipids, methods of their preparation as well as their uses in medical applications, wherein the ether-lipids are represented by general formula I ##STR00001##

The present invention is directed to a new class of lipids, more specifically ether-lipids having a polar headgroup, as well as vesicles comprising these lipids, methods of their preparation as well as their uses in medical applications, wherein the ether-lipids are represented by general formula I ##STR00001##