The present disclosure provides processes for preparing an alpha-hydroxy ester by addition of a vinyl Grignard reagent to an oxalate ester and thiolation of the resulting double bond. Also provided are alpha-hydroxy esters and synthetic intermediates prepared according to processes disclosed herein and compositions comprising the alpha-hydroxy esters.

The present disclosure provides processes for preparing an alpha-hydroxy ester by addition of a vinyl Grignard reagent to an oxalate ester and thiolation of the resulting double bond. Also provided are alpha-hydroxy esters and synthetic intermediates prepared according to processes disclosed herein and compositions comprising the alpha-hydroxy esters.

The invention relates to a process for the co-production of alkyl mercaptan and of dialkyl disulfide, comprising the following successive steps: a) reaction of a C.sub.1-C.sub.4 alcohol in the presence of hydrogen sulfide (H.sub.2S) to form a stream (M) comprising an alkyl mercaptan, water, and possibly unreacted hydrogen sulfide, b) purification of the stream (M) to obtain a stream (N) enriched in alkyl mercaptan, c) recovery of a first portion of the stream (N) including the alkyl mercaptan purified in step b), d) oxidation with sulfur of the second portion of the stream (N) of alkyl mercaptan, to form a stream (O) comprising a dialkyl disulfide, hydrogen sulfide, and possibly unreacted alkyl mercaptan, e) purification of the stream (O) to separate, on the one hand, the enriched dialkyl disulfide and, on the other hand, the hydrogen sulfide and possibly the alkyl mercaptan that has not reacted in step d), f) recycling of the hydrogen sulfide and possibly of the alkyl mercaptan isolated in step e) into the stream (M) obtained from step a), g) recovery of the dialkyl disulfide isolated in step e).

The invention features methods for the treatment of cystinosis and other cysteamine sensitive disorders in a subject including administration of a disulfide convertible to cysteamine in vivo. The methods can include the separate administration of a reducing agent to the subject to increase the bioavailablity and extend the plasma pharmacokinetic profile of the cysteamine produced following administration of the disulfide. The methods permit sustained cysteamine plasma concentrations in a subject.

The invention features methods for the treatment of cystinosis and other cysteamine sensitive disorders in a subject including administration of a disulfide convertible to cysteamine in vivo. The methods can include the separate administration of a reducing agent to the subject to increase the bioavailablity and extend the plasma pharmacokinetic profile of the cysteamine produced following administration of the disulfide. The methods permit sustained cysteamine plasma concentrations in a subject.

The invention features methods for the treatment of cystinosis and other cysteamine sensitive disorders in a subject including administration of a disulfide convertible to cysteamine in vivo. The methods can include the separate administration of a reducing agent to the subject to increase the bioavailablity and extend the plasma pharmacokinetic profile of the cysteamine produced following administration of the disulfide. The methods permit sustained cysteamine plasma concentrations in a subject.

The invention features methods for the treatment of cystinosis and other cysteamine sensitive disorders in a subject including administration of a disulfide convertible to cysteamine in vivo. The methods can include the separate administration of a reducing agent to the subject to increase the bioavailablity and extend the plasma pharmacokinetic profile of the cysteamine produced following administration of the disulfide. The methods permit sustained cysteamine plasma concentrations in a subject.

The present invention provides a compound of formula (I), formula (II), formula (III), (IV) or a salt thereof, compositions and methods of making the compound, methods and reagents for measuring the compound, and kits using the same. The use of a compound of formula (I), formula (II), formula (III), or formula (IV) for assessing or monitoring kidney function in a subject, determining predisposition to developing reduced kidney function, classifying a subject according to level of kidney function, and diagnosing or monitoring chronic kidney disease is also described.

The present invention provides a compound of formula (I), formula (II), formula (III), (IV) or a salt thereof, compositions and methods of making the compound, methods and reagents for measuring the compound, and kits using the same. The use of a compound of formula (I), formula (II), formula (III), or formula (IV) for assessing or monitoring kidney function in a subject, determining predisposition to developing reduced kidney function, classifying a subject according to level of kidney function, and diagnosing or monitoring chronic kidney disease is also described.

The invention concerns a synthesis process of a compound of the following formula (I) or one of the salts thereof,

##STR00001## wherein R represents a COOH, CH.sub.2OH or CHO group, comprising the step according to which the but-3-ene-1,2-diol (BDO) is subjected to an oxidation in the presence of a catalyst, said catalyst comprising an active phase based on at least one noble metal selected from palladium, gold, silver, platinum, rhodium, osmium, ruthenium and iridium, and a support containing alkaline sites.

The invention also concerns the application of this reaction to the preparation of bioavailable compounds of methionine used, in particular, in animal nutrition.