PROCESS FOR SYNTHESIZING FUNCTIONALIZED MERCAPTANS UNDER AN H2S PRESSURE

1 . Process for synthesizing at least one functionalized mercaptan of the following general formula (I): R 2 —X—C*H(NR 1 R 7 )—(CH 2 ) n —SH (I) in which,

R 1 and R 7 , which are identical or different, are a hydrogen atom or an aromatic or nonaromatic, linear, branched or cyclic, saturated or unsaturated, hydrocarbon chain of 1 to 20 carbon atoms which may comprise one or more heteroatoms;

X is chosen from —C(═O)—, —CH 2 — or —CN;

R 2 is:

(i) either absent when X represents —CN,

(ii) or a hydrogen atom,

(iii) or —OR 3 , R 3 being a hydrogen atom or an aromatic or nonaromatic, linear, branched or cyclic, saturated or unsaturated, hydrocarbon chain of 1 to 20 carbon atoms which may comprise one or more heteroatoms,

(iv) or —NR 4 R 5 , R 4 and R 5 , which are identical or different, being a hydrogen atom or an aromatic or nonaromatic, linear, branched or cyclic, saturated or unsaturated, hydrocarbon chain of 1 to 20 carbon atoms which may comprise one or more heteroatoms;

n is equal to 1 or 2; and * represents an asymmetric carbon;

said process comprising the stages of:

a) provision of at least one compound of the following general formula (II):

R 2 —X—C*H(NR 1 R 7 )—(CH 2 ) n - G   (II)

in which *, R 1 , R 2 , R 7 , X and n are as defined for formula (I) and

G represents either (i) R 6 —C(O)—O—, or (ii) (R 7 O)(R 8 O)—P(O)—O—, or (iii) R 9 O—SO 2 —O—; with

R 6 being a hydrogen atom or a linear, branched or cyclic, saturated or unsaturated hydrocarbon chain of 1 to 20 carbon atoms which may comprise one or more aromatic groups and may be substituted by one or more groups chosen from —OR 10 , (═O), —C(O)OR 11 , —NR 12 R 13 ;

R 10 , R 11 , R 12 and R 13 being independently chosen from:

H or a linear, branched or cyclic, saturated or unsaturated hydrocarbon chain of 1 to 20 carbon atoms;

R 7 and R 8 , which are identical or different, being a proton, an alkali metal, an alkaline earth metal or an ammonium;

R 9 being chosen from a proton, an alkali metal, an alkaline earth metal or an ammonium;

b) provision of H 2 S;

c) reaction between said at least one compound of formula (II) and H 2 S in the presence of at least one enzyme chosen from sulfhydrylases, preferably a sulfhydrylase associated with said compound of formula (II);

said reaction being performed in a reactor with a partial pressure of H 2 S in the gas headspace of said reactor of between 0.01 and 4 bars, for example between 0.01 and 3 bars, preferably between 0.1 and 3 bars, for example between 0.1 and 2.5 bars, at the reaction temperature;

d) obtaining of at least one functionalized mercaptan of formula (I);

e) optional separation of said at least one functionalized mercaptan of formula (I) which is obtained in stage d); and

f) optional additional functionalization and/or optional deprotection of the functionalized mercaptan of formula (I) which is obtained in stage d) or e); and

wherein stages a) and b) are optionally performed simultaneously.

2 . Synthesis process according to claim 1 , wherein the partial pressure of H 2 S in the gas headspace of said reactor is of between 0.25 and 2 bars.

3 . Synthesis process according to claim 1 , wherein the H 2 S is in excess relative to the compound of formula (II).

4 . Synthesis process according to claim 1 , wherein stage c) is carried out in aqueous solution.

5 . Synthesis process according to claim 1 , wherein the partial pressure of H 2 S corresponds to the total pressure in said gas headspace.

6 . Synthesis process according to claim 1 , wherein the partial pressure of H 2 S is kept constant throughout the entire duration of stage c).

7 . Synthesis process according to claim 1 , wherein the compound of formula (II) is chosen from the group consisting of:

O-phospho-L-homoserine, O-succinyl-L-homoserine, O-acetyl-L-homoserine, O-acetoacetyl-L-homoserine, O-propio-L-homoserine, O-coumaroyl-L-homoserine, O-malonyl-L-homoserine, O-hydroxymethylglutaryl-L-homoserine, O-pimelyl-L-homoserine and O-sulfato-L-homoserine, preferably O-acetyl-L-homoserine.

8 . Synthesis process according to claim 1 , wherein the functionalized mercaptan of formula (I) is L-homocysteine.

9 . Synthesis process according to claim 1 , wherein said compound of formula (II) is O-acetyl-L-homoserine, the enzyme used is O-acetyl-L-homoserine sulfhydrylase and the functionalized mercaptan of formula (I) is L-homocysteine.

10 . Process according to claim 1 , wherein stage c) is carried out essentially in the absence of oxygen, preferably in the absence of oxygen.

11 . Process according to claim 1 , wherein the temperature during stage c) is between 10° C. and 60° C., preferably between 20° C. and 40° C., and more particularly between 25° C. and 40° C.

12 . Composition comprising:

a compound of formula (II) as defined in claim 1 ;

a sulfhydrylase; and

dissolved H 2 S.