Title: A process for the Preparation of methionine

alpha-hydroxy analogues from sugars and derivatives thereof.

Description :

A process for the preparation of methionine a-hydroxy ana ^¬ logue and derivatives thereof from sugars in the presence of zeotype compounds . Background :

Carbohydrates represent the largest fraction of biomass and various strategies for their efficient use as a feedstock for the preparation of commercial chemicals are being estab- lished. Biomass is of particular interest due to its poten ^¬ tial for supplementing, and ultimately replacing, petroleum as a feedstock for such purposes. Carbohydrates obtainable from biomass comprise C2 to C6 sugars and are of particular interest industrially as they are a potential source of high- ly functionalised short chain carbon compounds.

This invention is directed towards the preparation of methio ^¬ nine a-hydroxy analogue and derivatives thereof from sugars in the presence of zeotype compounds. Methionine a-hydroxy analogue is 2-hydroxy-4- (methylthio) butanoic acid. Methio ^¬ nine a-hydroxy analogue and derivatives thereof may be used as a food/nutritional supplement in animal feed composi ^¬ tions/formulations . It is known that C2-C6 sugars may be converted to methyl lac ^¬ tate and methyl vinylglycolate (MVG) in the presence of zeo ^¬ type materials such as Sn-BEA. EP 2 184 270 Bl and Science (2010) 328, pp 602 - 605 report average yields of methyl lac- tate of 64%, 43% and 44% at 160 °C, in the presence of Sn-BEA and methanol from sucrose, glucose and fructose, respective ^¬ ly. Methyl vinylglycolate (MVG) is the major by-product with a reported yield of 3-11%. MVG may be produced in yields of up to 56% from the C4 sugar D-erythrose.

WO 98/32735 discloses a process for the preparation of methi ^¬ onine a-hydroxy analogue methyl ester, 2-hydroxy-4-

(methylthio) butanoic acid methyl ester, _r in cLn 85-6 yield via a free radical addition of methylthiol to a non- conjugated olefinic substrate, i.e. methyl vinylglycolate

(MVG) . Although high yielding, radical reactions have the po ^¬ tential to form region-isomeric by-products. WO 98/32735 also discloses an alternative, multi-step, com ^¬ mercially feasible process for preparing methionine a- hydroxy analogue, 2-hydroxy-4- (methylthio) butanoic acid.

The process comprises a Michael addition of methyl mercaptan to acrolein (a conjugated olefinic substrate) in the presence of an organic amine catalyst to produce 3- (methylthio) - propanal, followed by nitrile addition and hydrolysis to the acid. Although the process is industrially feasible, the use of toxic and expensive reagents such as HCN and acrolein should be avoided.

ChemCatChem (2013) 5, pp 569-575 discloses the conversion of tetroses (C4 sugars) to MVG and MMHB under homogenous cata ^¬ lytic conditions. MMHB is selectively produced from erythru- lose (C4 sugar) in the presence of a homogenous tin chloride catalyst. Accordingly, it is desirable to provide an alternative pro ^¬ cess for the preparation of methionine a-hydroxy analogue and derivatives thereof. In particular, it is desirable to provide a process that is industrially feasible, it is there- fore desirable that the process is high yielding, direct and selective. It is desirable that the process is carried out under conditions that are industrially feasible, with regents or catalysts that enable ease of production and reduced toxic waste, such as the use of heterogenous catalysts that may be regenerated. Additionally, the provision of a process wherein the substrates are derived from renewable sources such as C2- C6 sugars, is desirable. In particular because the sugar sub ^¬ strates are much less toxic and much cheaper than, for example acrolein and the HCN reagent, consequently the use of sugar substrates significantly lowers the costs of produc ^¬ tion.

Disclosure of the Invention It has surprisingly been found that a methionine a-hydroxy analogue and derivatives thereof is obtainable by contacting one or more sugars with a metallo-silicate composition in the presence of a compound comprising sulphur and a solvent. The methionine a-hydroxy analogue and derivatives thereof may be represented by the formula

R' -S-CH2-CH2-CHOH-COO-R (I),

wherein R is selected from the group consisting of H, Ci-Cs alkyl or alkaline or alkaline-earth metals; and R' is select- ed from the group consisting of H and methyl. The methionine a-hydroxy analogue and derivatives thereof may alternatively be ws:

It has surprisingly been found that a high yield of the me ^¬ thionine a-hydroxy analogue and derivatives thereof is ob ^¬ tainable according to the process of the present invention,

The compound comprising sulphur is preferably a compound of the formula RSR' , wherein R and R' are selected from the group consisting of H, C1-C5 alkyl or alkaline or alkaline- earth metals. The compound comprising sulphur is preferably selected from the group consisting of C ₁ -C5 alkyl thiol, C ₁ -C5 alkyl thiol salts, dimethylmercaptan, dimethyl disulphide and hydrogen sulphide. C ₁ -C5 alkyl thiol is in the present con ^¬ text meant to refer to mono-and di-substituted thiols with a substituent comprising a straight or branched chain saturated aliphatic alkyl group comprising one, two, three, four or five carbons. C ₁ -C5 alkyl thiol is in the present context meant to refer to an alkyl thiol selected from the group con ^¬ sisting of methane thiol, ethane thiol, straight or branched chain propane thiol, straight or branched chain butane thiol and straight or branched chain pentane thiol.

C ₁ -C5 alkyl thiol salt is in the present context meant to re fer to the alkali or alkaline earth metal salt of a C ₁ -C5 al kyl thiol. Specifically, C ₁ -C5 alkyl thiol salt is in the present context meant to refer to a C ₁ -C5 alkyl thiol in the salt form wherein the cation is selected from the group con- sisting of sodium, potassium, lithium, magnesium and calcium. Specifically, C ₁ -C5 alkyl thiol salt is in the present con ^¬ text meant to refer to a C ₁ -C5 alkyl thiol selected from one or more of the group consisting of NaSC¾, KSCH ₃ , Ca(SCH ₃ ) ₂ and Mg (SCH ₃ ) 2.

Hydrogen sulphide can be used as sulphur compound to produce 2-hydroxy-4-mercapto-butanoic acid or esters thereof, which can be further converted to the methionine a-hydroxy ana- logues by reaction with methanol. Alternatively, hydrogen sulphide can be used to form a C ₁ -C5 alkyl thiol in the pres ^¬ ence of the sugar, an alcohol and an acidic catalyst, as de ^¬ scribed in Roberts, J. S. 2000. Thiols, Kirk-Othmer Encyclo ^¬ pedia of Chemical Technology.

The methionine a-hydroxy analogue and derivatives thereof are selected from the group consisting of 2-hydroxy-4- (C ₁ -5 alkylthio) butanoic acid, salts and esters thereof. C ₁ -5 al- kylthio corresponds to the C ₁ -5 alkyl thio compound comprising sulphur present in the process. Preferably, the methionine a-hydroxy analogue and derivatives thereof are selected from the group consisting of 2-hydroxy-4- (methylthio) butanoic ac ^¬ id, salts and esters thereof. Preferably, the methionine a- hydroxy analogue and derivatives thereof are selected from the group consisting of 2-hydroxy-4- (methylthio) butanoic ac ^¬ id, alkali and alkaline earth metal salts and Ci-8 alkyl es ^¬ ters thereof. Preferably, the methionine a-hydroxy analogue and derivatives thereof are selected from the group consist ^¬ ing of 2-hydroxy-4- (methylthio) butanoic acid, alkali and al- kaline earth metal salts and Ci-8 alkyl esters thereof. Ci-8 alkyl esters is in the present context meant to refer to esters comprising the alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, isopropyl, isobu- tyl, pentyl, hexyl, heptyl, octyl and 2-ethylhexyl . Alkali and alkaline earth metal salts mean salts of the acid wherein the salt cation is selected from the group I and group II metals .

In one embodiment of the invention the methionine a-hydroxy analogue and derivatives thereof is 2-hydroxy-4- (methylthio) butanoic acid.

In a another embodiment of the invention the methionine a- hydroxy analogue and derivatives thereof is selected from the group consisting of 2-hydroxy-4- (methylthio) butanoic acid me ^¬ thyl ester, 2-hydroxy-4- (methylthio) butanoic acid ethyl es ^¬ ter, 2-hydroxy-4- (methylthio) butanoic acid propyl ester, 2- hydroxy-4- (methylthio) butanoic acid butyl ester, 2-hydroxy-4- (methylthio) butanoic acid isopropyl ester, 2-hydroxy-4- (methylthio) butanoic acid pentyl ester, 2-hydroxy-4-

(methylthio) butanoic acid hexyl ester, 2-hydroxy-4- (methylthio) butanoic acid heptyl ester, 2-hydroxy-4- (methylthio) butanoic acid octyl ester and 2-hydroxy-4- (methylthio) butanoic acid 2-ethylhexyl ester.

The one or more sugars or derivatives thereof are selected from the group consisting of C2-C6 sugars or derivatives thereof. C2-C6 sugars or derivatives thereof is in the pre ^¬ sent context meant to refer to carbohydrates commonly found in biomass selected from the group consisting of glucose, fructose, galactose, mannose, sucrose, xylose, erythrose, erythrulose, threose, glycolaldehyde and 2-hydroxy-y- butyrolactone . The one or more sugars or derivatives thereof may be used in solution or it may be a sugar syrup. Such a solution and syrup may be referred to as a sugar composition. The sugar composition may contain the solvent. Accordingly, the one or more sugars and derivatives thereof may be mixed with the solvent and/or the compound comprising sulphur, before it is contacted with the metallo-silicate composition. It may be referred to as a reaction mixture. The process is preferably a one step process wherein the me ^¬ thionine a-hydroxy analogue and derivatives thereof are ob ^¬ tainable directly from the sugar substrate by contacting one or more sugars with a metallo-silicate composition in the presence of a compound comprising sulphur and a solvent.

In a further embodiment of the invention the sugars can be used in the presence of other C ₁ -C3 oxygenates such as, ace- tol, pyruvaldehyde, formaldehyde and glyoxal. Glycolaldehyde (C2 sugar) can be produced together with minor amounts of other C ₁ -C3 oxygenates by hydrous thermolysis of sugars ac ^¬ cording to the procedure described in US 7,094,932 B2 and PCT/EP2014/053587.

The methionine a-hydroxy analogue and derivatives thereof are also obtainable by subjecting the one or more sugars or derivatives thereof to a pyrolysis step to obtain a pyrolysis product and subsequently contacting the pyrolysis product with the metallo-silicate composition in the presence of the compound comprising sulphur and the solvent.

Metallo-silicate composition refers to one or more solid ma ^¬ terials comprising silicon oxide and metal and/or metal oxide components, wherein the metal and/or metal oxide components are incorporated into and/or grafted onto the surface of the silicon oxide structure (i.e. the silicon oxide structure comprises M-O-Si bonds) . The silicon oxide structure is also known as a silicate. Metallo-silicate compositions may be crystalline or non-crystalline. Non-crystalline metallo- silicates include ordered mesoporous amorphous or other meso- porous amorphous forms. The metallo-silicate composition is selected from one or more of the group consisting of zeotype materials and ordered mesoporous amorphous silicates.

Preferably the active metal of the metal and/or metal oxide component is selected from one or more of the group consist ^¬ ing of Ge, Sn, Pb, Ti, Zr and Hf. The genus of zeotype mate- rials encompasses the zeolite material genus. Preferably the zeotype material has a framework structure selected from the group consisting of BEA, MFI, FAU, MOR and FER. Preferably the ordered mesoporous amorphous silicate has a structure se ^¬ lected from the group consisting of MCM-41 and SBA-15. In a preferred embodiment, the metallo-silicate composition is a zeotype material. More preferably the metallo-silicate compo ^¬ sition is a zeotype material and is selected from the group consisting of Sn-BEA, Sn-MFI, Sn-FAU, Sn-MCM-41 and Sn-SBA- 15.

The solvent is preferably selected from one or more of the group consisting of methanol, ethanol, 1-propanol, 1-butanol, 2-propanol, 2-butanol, DMSO and water. WO 2015/024875 discloses that in certain conditions, the presence of a metal ion in the reaction solution is benefi ^¬ cial to the yield. WO 2015/024875 provides experimental de- tails describing the origin and addition of the metal ion to the process either via the catalyst itself or independently of the catalyst. A further embodiment of the present invention is a basic re ^¬ action solution. The basic solution may be obtainable by the addition of one or more basic components. The basic component may be selected from one or more of the reagents selected from a metal salt and a basic polymer resin. Basic polymer resin may be for example a basic amberlyst resin.

The metal salt comprises a metal ion. Preferably the metal ion is selected from the group consisting of potassium, sodium, lithium, rubidium and caesium. Preferably the metal salt is a salt of an alkaline earth metal or alkali metal and ani ^¬ on is selected from the group consisting of carbonate, ni ^¬ trate, acetate, lactate, chloride, bromide and hydroxide. Even more preferably the metal ion originates from one or more salts of the alkaline earth metal or alkali metal and is selected from the group consisting of K ₂ CO ₃ , KNO ₃ , KC1, potas ^¬ sium acetate (CH ₃ CO ₂ K) , potassium lactate (CH ₃ CH (OH) CO ₂ K) , Na ₂ C0 ₃ , Li ₂ C0 ₃ and Rb ₂ C0 ₃ .

The reaction vessel/solution that is used in the process is heated to a temperature of less than 250 °C . Preferably the vessel is heated to from 50 °C to 180 °C, from 60 °C to 170 °C, from 80 °C to 150 °C; more preferably from 60 °C to 140 °C. According to the process of the present invention the inven ^¬ tors have surprisingly found that the yield of the methionine a-hydroxy analogue and derivatives thereof is greater than than the yield of MVG. If a C4 saccharide is the substrate, the yield of MVG is less than 5%, 4%, 3%, 2%, 1%.

Also, the inventors have surprisingly found that the yield of the methionine a-hydroxy analogue and derivatives thereof prepared according to the process of the present invention is greater than 15%.

The process for the preparation of methionine a-hydroxy ana- logue and derivatives thereof may be carried out in a batch scale reaction or a continuous flow reaction.

The one or more sugars or derivatives thereof are contacted with the metallo-silicate composition in the presence of the compound comprising sulphur and the solvent in a reactor.

Sugars or derivatives thereof are gradually converted into the methionine a-hydroxy analogue and derivatives thereof. Preferably the reactor is stirred such as by a mixer or by the flow through the reactor. The conversion is preferably carried out under heating and for a period of time sufficient to achieve a high conversion of the sugars and derivatives thereof. Preferably for a period of from 10 minutes to 12 hours, more preferred of from 20 to 300 minutes. The methio ^¬ nine a-hydroxy analogue and derivatives thereof may be re- covered as it is or it may be purified such as by distilla ^¬ tion.

Products obtained from bio materials such as sugars, will have a significantly higher content of ¹⁴ C carbon than the same products obtained from petrochemical sources. Previous- ly, methionine and its derivatives for use as nutritional supplements have been obtained from fossil fuels. Accordingly a product is provided according to the present invention, which is obtainable by the process for the prepa ^¬ ration of a methionine a-hydroxy analogue and derivatives thereof from sugars described above. Such a product is char- acteristic by having a ¹⁴ C content above 0.5 parts per tril ^¬ lion of the total carbon content. The methionine a-hydroxy analogue and derivatives thereof may be 2-hydroxy-4- (methylthio) butanoic acid, salts and esters thereof and at least 70% of the initial carbon may be recovered in that form.

Legends to the Figures

Figure 1. Yield of methyl ester of methionine a -hydroxy ana- logue (2-hydroxy-4- (methylthio) butanoic acid methyl ester) with Sn-Beta as catalyst using glycolaldehyde as sugar in continuous flow reaction. Feed composition: 9 g/L glycolaldehyde in methanol as solvent, 10.7 wt% of water, 0.9 g/L me- thanethiol .

Figure 2. Yield of methyl ester of methionine a -hydroxy ana ^¬ logue (2-hydroxy-4- (methylthio) butanoic acid methyl ester) with Sn-Beta as catalyst using glycolaldehyde in the presence of C1-C3 oxygenate compounds in continuous flow reaction.

Feed composition: 10.9 g/L glycolaldehyde in methanol as sol ^¬ vent, 8 wt% of water, 0.7 g/L methanethiol .

Examples

Preparation of catalyst Sn-BEA (Si/Sn = 125) is prepared according to a modification of the procedure described in US 4,933,161. Commercial zeo ^¬ lite Beta (Zeolyst, Si/Al 12.5, ammonium form) is calcined

(550°C for 6 h) to obtain the H form (de-aluminated form) and treated with 10 grams of concentrated nitric acid (Sigma- Aldrich, 65%) per gram of zeolite beta powder for 12 h at 80°C. The resulting solid is filtered, washed with ample wa ^¬ ter and calcined (550°C for 6 h) to obtain the de-aluminated Beta. This solid is impregnated by incipient wetness method- ology with a Sn/Si ratio of 125. For this purpose, tin (II) chloride (0.128 g, Sigma-Aldrich, 98%) is dissolved in water

(5.75 mL) and added to the de-aluminated Beta (5 g) . After the impregnation process, the samples are dried 12 h at 110 °C and calcined again (550°C for 6 h)

Example 1 : Catalytic reaction in batch reaction

A stainless steel pressure vessel (40 cc, Swagelok) is charged with 15.0 g of methanol (Sigma-Aldrich, >99.8%), 0.450 g of sucrose (Fluka, >99.0%) and 0.150 g of catalyst.

The reactor is then filled with 75 mL of methanethiol at 1.7 bar, pressurized at 11 bar with 2 and closed. The reactor is heated in an oil bath at 170 °C under stirring (700 rpm) . The reaction is continued for the desired time and after this pe- riod, the reaction is quenched by submerging the vessel in cold water. Samples from the reaction vessel are filtered and analysed by HPLC (Agilent 1200, Biorad Aminex HPX-87H column at 65 °C, 0.05 M H ₂ SO ₄ , 0.6 ml min ^-1 ) to quantify unconverted hexoses and dihydroxyacetone (DHA) , glyceraldehyde (GLA) ; and GC (Agilent 7890 with a Phenomenex Solgelwax column) was used to quantity: methyl lactate (ML) , methyl vinylglycolate (MVG, methyl 2-hydroxy-3-butenoate) , glycolaldehyde dimethylacetal (GADMA) and MHA (Methionine a-hydroxy analogue and deriva ^¬ tives thereof) .

The methionine a-hydroxy analogue esters prepared according to Example 1 may be reacted in a basic aqueous solution, such as aqueous NaOH or KOH or an acidic aqueous solution, such as aqueous HC1, or solid acid catalyst to produce the salts and the acid derivatives of the methionine α-hydroxy analogue ester .

Table 1: Conversion of sugars to methionine α-hydroxy ana ^¬ logue and derivatives thereof in the Presence of a Metallo- silicate composition and sulfur compound. MHA means methio ^¬ nine g-hydroxy analogue and derivatives thereof. In the case of solvents A, B and C, MHA means 2-hydroxy-4-

(methylthio) butanoic acid methyl ester. In the case of H20 as solvent, MHA means 2-hydroxy-4- (methylthio) butanoic acid. In the case of IPA, MHA means 2-hydroxy-4- (methylthio) butanoic acid isopropyl ester. In the case of ethanol, MHA means 2- hydroxy-4- (methylthio) butanoic acid ethyl ester.

Sugar Catalyst SolCH3SH MHA MVG ConverTemp Time vent / mL Yield Yield sion

Erythrulose Sn-BEA A 25 20.7 0 68.1 60 16

Erythrulose Sn-BEA A 25 6.8 0 43.8 60 4

Erythrulose Sn-BEA A 50 3.5 0 14.0 60 4

Erythrulose Sn-BEA A 25 24.3 0 77.7 100 4

Erythrulose Sn-BEA A 25 11.4 0 86.6 60 4

Erythrulose Sn-BEA A 25 12.7 17.4 93.8 170 16

Erythrulose Sn-MFI A 25 29.1 0 81.3 100 4

Erythrulose Sn-FAU A 25 0 0 54.0 100 4

Erythrulose Sn-MOR A 25 0 - 97.2 100 4

Erythrulose Sn-BEA IPA 25 0 0 66.7 100 4

Erythrulose Sn-BEA EtOH 25 15.6 0 68.7 100 4

Erythrulose Sn-BEA H20 25 0 0 0 80 4

Erythrulose Sn-BEA A 25 21.2 0 76.6 140 4

Erythrulose Sn-BEA A 50 19.7 8.3 85.7 170 4

Erythrulose Sn-BEA A 25 6.7 0 27.4 60 4

Erythrulose Sn-BEA A 25 14.8 0 84.6 170 4

Erythrulose Sn-BEA B 25 23.7 0 73.0 100 4

Erythrulose Sn-BEA C 25 22.1 0 76.9 100 4

Glucose Sn-BEA A 25 3.6 «1 0 160 3

Glucose Sn-BEA A 25 8.3 0 100 160 4

Glucose Sn-BEA A 25 5.0 5.8 96.8 170 16

GA Sn-BEA A 25 12.7 0 44.3 120 4

GA Sn-BEA A 25 17.4 0 41.9 120 16

GA Sn-BEA A 25 14.9 5.4 30.7 140 16

GA Sn-BEA A 10 7.5 0 48.0 60 4

GA Sn-BEA A 25 5.0 0 8.4 60 4

GA Sn-BEA A 25 17.7 4 28.9 60 3

GA Sn-BEA H20 25 0 0 51.3 80 4 Ex Sugar Catalyst SolCH3SH MHA MVG ConverTemp Time vent / mL Yield Yield sion

29 GA Sn-BEA A 25 0 0 39.4 60 4

30 GA Sn-BEA A 25 0 0 52.3 60 4

31 GA Sn-BEA A 10 0 0 51.1 60 4

32 GA Sn-BEA B 25 0 0 46.5 60 4

33 GA Sn-BEA C 25 5.0 0 88.9 120 4

34 GA Sn-BEA A 25 8.3 0 62.1 120 4

35 Sucrose Sn-BEA A 25 2.0 4.2 96 170 16

36 Sucrose Sn-BEA A 25 0.9 0 72.8 160 3

37 MVG Sn-BEA A 25 0 0 100 4

38 MVG Sn-BEA A 25 0 100 100 4

39 MVG Sn-BEA A 25 0.2 12.7 170 16

40 Erythrose Sn-BEA A 25 0 0 0 60 4

41 Erythrose Sn-BEA A 25 20.0 0 80.0 100 4

42 Erythrose Sn-BEA A 25 19.3 0 94.0 170 4

43 GA Sn-BEA A 25 14.5 0 73.0 100 16

44 GA Sn-BEA & A 25 15.4 0 90.1 100 16

Amberlyst

45 Glucose Sn-BEA A 85 8.3 - 79.4 120 4

46 Erythrulose Sn-BEA A 85 17.0 - 81.8 120 4

Solvent A: MeOH+0.13mmol K2C03

Solvent B: MeOH+0.06mmol K2C03

Solvent C: MeOH+0.3mmol K2C03

GA = glycolaldehyde As observed in Table 1, C4 and C2 sugars (erythrulose and glycolaldehyde) provided the highest yields of methionine a- hydroxy analogue and derivatives thereof. Methanol and etha- nol provided similar yields of the corresponding esters. Example 2 : Catalytic reaction in continuous flow reaction

Compositions comprising glycolaldehyde in the presence of Ci- C3 oxygenate compounds may be prepared by pryrolysis of bio- mass or C5-C6 sugars such as glucose, sucrose, fructose or xylose. Exemplary pyrolysis reactions are provided in US 7,094,932 B2 and PCT/EP2014/053587. A composition comprising glycolaldehyde or C ₁ -C3 oxygenate compounds with 814 g/L glycolaldehyde was dissolved in metha ^¬ nol ( Sigma-Aldrich, 99.9%) at room temperature to reach a concentration of 10.9 g/1. Additionally, methanethiol (Sigma, 1.7 bar) and if necessary water, were added to the feed solu- tion. Catalyst Sn-Beta (Si:Sn 125) prepared according to the above preparation was fractionized (0.25 g, 300-600 ym.) and loaded into a stainless steel 0.25 inch reactor. Glass wool was used to hold the catalyst in place. The reactor was in ^¬ troduced into an oven and the temperature of the reactor in- creased to 160 °C. When the temperature was over 140°C, the pump was started with a flow of 0.05 ml/min.

As observed from figures 1 and 2, stable yields of 2-hydroxy- 4- (methylthio) butanoic acid methyl ester (over 30%) were ob- tained from glycolaldehyde in water and methanol using Sn- Beta as catalyst. The presence of other C1-C3 oxygentes (Fig ^¬ ure 2) did not affect the reaction of production of the me ^¬ thionine a -hydroxy analogue methyl ester. Embodiments

The present invention may also be described according to the following embodiments: Embodiment 1. A process for the preparation of methio ^¬ nine a-hydroxy analogues comprising contacting one or more sugars or derivatives thereof with a metallo- silicate composition in the presence of a compound com- prising sulphur and a solvent.

Embodiment 2. The process according to embodiment 1, wherein the compound comprising sulphur is selected from the group consisting of C ₁ -C5 alkyl thiol, C ₁ -C5 alkyl thiol salt, dimethylmercaptan, dimethyl disulphide and hydrogen sulphide.

Embodiment 3. The process according to any one of em ^¬ bodiments 1 and 2, wherein the compound comprising sul ^¬ phur is selected from the group consisting of methane thiol, dimethylmercaptan, dimethyl disulphide and hydro- gen sulphide.

Embodiment 4. A process according to any one of embodi ^¬ ments 1 to 3, wherein the one or more sugars or deriva ^¬ tives thereof is selected from the group consisting of glucose, fructose, galactose, mannose, sucrose, xylose, erythrose, erythrulose, threose, glycolaldehyde and 2- hydroxy-y-butyrolactone .

Embodiment 5. A process according to any one of embodi ^¬ ments 1 to 3, wherein the one or more sugars or deriva ^¬ tives thereof are derivatives obtained by subjecting one or more sugars selected from the group consisting of glucose, fructose, galactose, mannose, sucrose, xylose, erythrose, erythrulose, threose; to a pyrolysis step to obtain a pyrolysis product and subsequently contacting the pyrolysis product with the metallo-silicate composi- tion in the presence of the compound comprising sulphur and the solvent Embodiment 6. The process according to any one of em ^¬ bodiments 1 to 5, wherein the metallo-silicate composi ^¬ tion is a zeotype material.

Embodiment 7. The process according to embodiment 6, wherein the zeotype material is one or more materials selected from the group consisting of Sn-BEA, Sn-MFI, Sn-FAU, Sn-MCM-41 and Sn-SBA-15.

Embodiment 8. The process according to any one of em ^¬ bodiments 1 to 7, wherein the solvent is selected from one or more of the group consisting of methanol, etha- nol, 1-propanol, 1-butanol, 2-propanol, 2-butanol, DMSO and water.

Embodiment 9. The process according to any one of em ^¬ bodiments 1 to 8, wherein the methionine a-hydroxy ana- logues is selected from the group consisting of 2- hydroxy-4- (methylthio) butanoic acid, salts and esters thereof .

Embodiment 10. The process according to any one of em ^¬ bodiments 1 to 9, wherein the methionine a-hydroxy ana- logues is selected from the group consisting of 2- hydroxy-4- (methylthio) butanoic acid, 2-hydroxy-4- (methylthio) butanoic acid methyl ester and 2-hydroxy-4- (methylthio) butanoic acid ethyl ester

Embodiment 11. The process according to any one of em- bodiments 1 to 10, wherein the temperature of the pro ^¬ cess is less than 200°C, preferably within the range of from 50 to 200°C.

Embodiment 12. The process according to any one of em ^¬ bodiments 1 to 11, wherein the reaction solution com- prises one or more basic components selected from the group consisting of a metal salt and a polymer resin. Embodiment 13. The process according to any one of em ^¬ bodiments 1 to 12, wherein the yield of the methionine a-hydroxy analogues is greater than methyl vinylglyco- late (MVG) .

Embodiment 14. The process according to any one of em ^¬ bodiments 1 to 13, wherein the yield of the methionine a-hydroxy analogues is greater than 15%.

Embodiment 15. The process according to any one of em ^¬ bodiments 1 to 14, wherein the process is a continuous process .

Embodiment 16. The process according to any one of em ^¬ bodiments 1 to 15, wherein the methionine a-hydroxy an ^¬ alogues are purified by distillation.

Embodiment 17. The process according to embodiment 9, wherein the 2-hydroxy-4- (methylthio) butanoic esters are hydrolysed .

Embodiment 18. Use of 2-hydroxy-4- (methylthio) butanoic acid, salts and esters thereof prepared by the process of claims 9 to 17 for a nutritional supplement.