DE3924257A1 - New tri:alkoxy-silyl derivs. - which are of aminoacid(s), sugars, etc. useful as protected intermediates - Google Patents

Abstract

Trialkoxysilyl derivs. of formula RxSi(OR1)3 (I) are new; where R= the residue of an amino acid, peptide or sugar of formula RXH, or a 1-24C hydrocarbon gp. which is opt. substd. by amino, oxo, thio (sic) gps. and/or interrupted by O, N or S; R1 = 1-4C alkyl; X= O or S. Pref. (I) area amino acid trialkoxysilyl esters, or amino acid or sugar trialkoxysilyl ethers. USE/ADVANTAGE - (I) are useful as protected intermediates, e.g. in the synthesis of peptides or sugar derivs.. For example, N-Boc-aspartic acid beta-(tri-t-butoxysilyl) ester is useful as an intermediate for the sweetener aspartane. Trialkoxysilyl protecting gps. are easy to introduce and remove, and the protected intermediates are easily isolated and have good stability in aq. media and good solubility in organic solvents.

Description

The invention relates to silicone esters of the general formula (1)

R-X-Si (O-R¹) ₃ (1)

in which

R - the residue of an amino acid, a peptide or a sugar of the general formula RXH
R¹ - an alkyl of 1 to 4 carbon atoms and
X - an oxygen or sulfur atom

mean.

Among the rest of an amino acid of the formula R-X-H, for example a residue of alanine, arginine, asparagine, aspartic acid, of cysteine, cystine, glutamine, glutamic acid, glycine, histidine, Hydroxyprolins, Isoleucins, Leucins, Lysins, Methionins, Ornitins, Phenylalanins, Prolins, Serins, Threonins, Tryptophans, Tyrosins, Valins etc. are understood.

Among the rest of a peptide, for example, a residue of one of the Amino acids listed above formed di-, tri- or tetrapeptide be understood.

Under the sugar residue R, the rest of a sugar R-X-H, such as. B. a pentose, a hexose or one of their usual derivatives will.

Suitable residues are given, for example, by an amino and / or if oxo, thio group substituted and / or by oxygen and optionally by nitrogen or sulfur atoms broken hydrocarbon residues with a maximum of 24 carbon atoms.  

Suitable radicals R are, for example, either

• - by one or two unprotected or protected in the usual way Amino groups and optionally one by an unprotected or protected carboxyl group substituted 1-oxoalkyl radical, alkyloxy radical or alkylthio radical with a maximum of 10 carbon atoms, or
• - by an unprotected or normally protected amino group and a optionally protected in the usual way hydroxyl substituted phenyl, indoyl or imidazolyl group 1-oxoalkyl radical with a maximum of 3 carbon atoms, or
• Peptide residues which are composed of 2 to 4 amino acids R-X-H, which contain the radicals R mentioned above, or
• - by unprotected or possibly protected in the usual way Hydroxy group-containing methyl or ethyl tetrahydrofuran or methyl tetrahydropyran residues.

Under a conventionally protected hydroxyl or amino group are understood those described in Houben-Weyl "Methods of Organic Chemistry ", Vol. 14 and Vol. 15, are listed.

Suitable protective groups for the hydroxyl group are, for example Acyl radicals with 1-8 carbon atoms such as the formyl radical, acetyl radical, the trimethylacetyl radical or the benzoyl radical, 1-alkoxyalkyl radicals with 2-6 carbon atoms such as methoxymethyl, 2-tetrahydro pyranyl radical or alkyl radical with 1-6 carbon atoms such as t-butyl, t-amyl, benzyl, etc.

Suitable protective groups for the amino groups are, for example Uretan type protecting groups such as Boc, Fmoc, Z and similar protection groups.

Suitable protective groups for the carboxyl group are, for example, the Benzyl or t-butyl radical.  

As radicals RX- the silicone ester of the general formula I may be mentioned as examples: Ala-O-, Arg (NO₂) O-, Arg (Z) O-, D-Arg (Tos) O-, AsnO-, AspO-, Asp (O ^t Bu) O-, Asp (O-) OH, D-Asp (O-) OH, Boc-Asp (O-) OH, Z-Asp (O-) OH, Fmoc-Asp (O-) OH , CysO-, CysOH, Cys [Si (O ^t Bu) ₃] O-, Cys (TRT) O-, Boc-CysOH, Fmoc-CysOH, GluO-, D-GluO-, Glu (O-) OH, D -Glu (O-) OH, BocGlu (O-) OH, FmocGlu (O-) OH, Fmoc-D-Glu (O-) OH, SerOH, Ser [Si (O ^t Bu) ₃] O-, Boc- SerOH, Fmoc-SerPH, PheO-, TyrO-, Tyr [Si (O ^t Bu) ₃] O-, TyrOH, Boc-TyrOH, FmocTyrOH, ThrOH, Fmoc-Ala- SerOH, Boc-Asp (O -) - PheOEt , Boc-Glu (O -) - ValO ^t Bu aa Abbreviations according to desire "Methods of Organic Chemistry" (Houben-Weyl) Volume XV / 1 (1974), pp. 1-27; and IUPAC-IUB nomenclatures, J. Biol. Chem. 260, pp. 14-42.

Because of their surprisingly good stability and shelf life these compounds are not only used as intermediates Synthesis of peptides and sugars find application, but also can be used directly as industrial chemicals.

In many areas of organic chemistry, for example peptide and sugar synthesis, where often a conversion to unwanted Functions is a selective blocking of such functions the crucial problem. This will be more complicated if after the corresponding reaction step a milder release of Protection group should take place. Handling selective blocking of page groups and the response to desired functions of the Compound and a mild deblocking after the reaction step therefore of particular importance. There are already many protection methods known that are suitable for reversible blocking, for. B. the benzyl, t-butyl or 9-fluorenylmethyl method. Nevertheless, these are protections methods are burdened with numerous disadvantages, which a. significant costs, a number of difficulties in synthesis or cleavage, as well as an additional cleaning of substrates and products.  

The silicone esters - especially trimethylsilyl esters - are in the organic Synthesis of great importance and are called hydroxyl protecting groups used in alcohols, phenols or carboxylic acids. The great instability of trimethylsilyl esters and other silicone esters is nevertheless a disadvantage. As a result, they are usually un protective groups useful. In addition, the silicone protection method requires stricter anhydrous (hydroxyl free) reaction conditions (e.g. can completely decompose humidity Silylester in a few minutes what has practical and technical difficulties and the Production costs increases.

In our studies on peptide synthesis and new protection We have synthesized new trialkoxysilyl esters using neutral methods Media are surprisingly stable and excellent as protective groups own. For example, B. the tri-tert-butoxysilanol in conjunction with the Side chain functions of amino acids such as aspartic acid, glutamine acid, serine, threonine, tyrosine, hydroxyproline, cysteine and the like and / or with their α-carboxyl group so stable derivatives that they Wash with water, diluted acids and bases without decomposition leave and even crystallize in water. The connections tri-tert Butoxysilanol with amino acids dissolve and tolerate popular solutions medium in peptide synthesis, such as. B. methylene chloride or di methylformamide. Your free amino group easily reacts with those in the Peptide chemistry mostly used acylating agents or amino group Protection reagents (Z, Boc or Fmoc reagents). The tri-alkoxy sililoxy, especially tri-tert-butoxysililoxy protecting group splits very quickly in solutions with strong acids, such as. B. hydrogen chloride, so that the tert-butoxy trigger known in peptide chemistry, namely trifluoroacetic acid in methylene chloride (1: 1), the protected Group separates in 1 minute.

For the process according to the invention, oligofunctional organi  cal compounds are used which have at least one hydroxyl group and / or phenol, carboxyl, thiol group, among others Own groups. The amino acids which in addition to the amino and carboxyl group another function in the side chain have: aspartic acid, glutamic acid, serine, threonine, Cysteine, tyrosine, hydroxyproline or the like. Most of the time, however α-carboxyl group in amino acids are protected. It is suitable for this Trialkoxysilyloxyester very good.

The tri-alkoxysilyloxy esters are made in uncomplicated processes Silicon tetrachloride or other active silicon compounds (see e.g. Gmelin's Handbook of Inorganic Chemistry, Silicon, Part C, p. 371 ff. [1958]) with corresponding alcohols R′-X-H (see e.g. N. Dolgov et al., Zhur. Obshchei Khim. 27, p. 921 [1957]; C.A. 1958, 3673i). This reaction step could either be in inert solvents such as Toluene, acetone, dioxane, tetrahydrofuran, methylene chloride, chloroform and with common solvents or simply in excess of R'-O-H alcohols (R 'has the meaning given above) will. Bases such as pyridine, dimethylaniline, Na, K-alcoholates, alkylamines or ammonia (see e.g. C.S. Miner et al., Ind. Closely. Chem. 39, p. 1368 [1947]) was used.

The suitable reaction temperatures are of R'-O-H used Alcohol dependent and are usually in the range of 0 ° -100 ° C.

The inventive method is characterized in that a corresponding compound R-X-H (where R and X have the above meaning have) with silicon tetrachloride in an excess of alcohol and optionally organic bases - such as pyridine, dimethylaniline, Na, K-alcoholates, amines or ammonia - at one reaction temperature from preferably 0 ° to 50 ° C. After that, the implementation product by means of extraction, chromatography or crystallization isolated.  

In a preferred variant of the method, the substrate, for. Legs Amino acid or a sugar, in an alcohol / pyridine solution with an appropriate amount of the trialkoxysilicon chloride and isolating the product in a known manner.

The method according to the invention has numerous advantages:

• 1. Simple and inexpensive introduction of the trialkoxysilyl protective group
• 2. Selective blocking of the functional group in addition to other free ones groups
• 3. uncomplicated isolation of protected connections
• 4. good solubility of the protected compounds, mostly also not polar solvents
• 5. very satisfactory stability of the connections during storage and during the chemical reaction
• 6. very simple, fast and uncomplicated splitting off of the protection group
• 7. very good protection due to the larger extent of the Trialkoxysilyl group, which is particularly the case with aspartic acid see is.

The following examples further illustrate the invention, but without the Limit claims.

Example 1 Tri-tert-butoxysilyl chloride

To a solution of 240 ml of anhydrous pyridine in 1000 ml of tert-butanol 110 ml of silicon tetrachloride are added dropwise while cooling in an ice bath slowly that the temperature of the reaction does not exceed 40 ° C. Then the mixture reacts for 2 hours at room temperature and 10 hours at 50 ° C. Filtered after cooling to normal temperature the white crystals (pyridine hydrochloride) and the solution that which contains tri-tert-butoxysilicon chloride, can be used for protecting groups introduction. The pure tri-tert-butoxychloride is obtained by distillation under reduced pressure (126-128 ° C at 10 Torr).

Example 2 L-Aspartic acid β- (tri-tert-butoxysilyl) ester

1.33 g of aspartic acid are dissolved in 20 ml of tri-tert-butoxysilicon chloride (according to Example 1) dissolved, which normally take 1 day can. 50 ml of toluene are added to the clear solution obtained and thicken the substance on a rotary evaporator. The oil obtained with partially white white crystals is diluted with 100 ml of ethyl acetate and with water, then with saturated sodium bicarbonate and again washed with water. The organic layer is now separated and dried with sodium sulfate, then concentrated with toluene. The glass like gel is sucked off in the Schott funnel, ground with toluene and vacuumed again. The substance is still chromato on silica gel 60 graphically cleaned by rinsing out first with toluene, then with a gradient of acetone in toluene and in the end only with acetone. 1.9 g of white powder are obtained.  

The analysis clearly shows the title link.

Elemental analysis: Molecular weight C₁₆H₃₃NO₇Si · ½ H₂O = 388.5
Ber. C 49.46; H 8.82; N 3.60;
Found: C 49.57; H 8.64; N 3.44.

Mass spectrum (FAB method in DMSO glycerin): m / 3 = 378 and dimer 758.
NMR (CDCl₃), δ: 1.32, 1.40, 1.42 (m, 27 H), 292-3.20 (m, 2 H), 3.84-4.00 (m, 1 H), 6.00-7.50 (very broad, 2 H )
IR (in KBr) cm ^-1 : 3975, 1725, 1635, 1385, 1365, 1243, 1190, 1080 (wide) and others
= -10.0 ° ± 0.5 ° (C = 12 in CHCl₃)

Example 3 tert-Butoxycarbonyl-L-aspartic acid β- (tri-tert-butoxysilyl) ester

379 mg (1 mmol) of aspartic acid β-silylester (according to Example 2) are dissolved in 4 ml of tert-butanol and 0.15 ml of triethylamine and the mixture 1 React with 0.25 ml of di-tert-butyl dicarbonate per day. After that it will evaporated tert-butanol with toluene under reduced pressure, so oil obtained dissolved in ethyl acetate, washed with 2% citric acid and dried with sodium sulfate. 0.2 ml is added to the solution Dicyclohexylamine together with ligroin and constricts it under reduced Pressure. The product thus obtained is crystallized from ligroin. Man receives 568 mg of white crystals that melt at 149 ° C.

Elemental analysis: molar mass C₃₃H₆₄N₂O₉Si = 660.94
Ber. C 59.96; H 9.76; N 4.24;
Found: C 60.01; H 9.73; N 4.05.

NMR (CDCl₃), δ: 0.84-2.10 (m, 10 H), 1.28 (s, 27 H), 1.46 (s, 9 H), 2.88-3.08 (m, 4 H), 4.16 (dd, 1 H) , 5.68 (d, 1H)
IR (in KBr) cm ^-1 : 3425, 3270, 2975, 2935, 2860, 1740, 1710, 1635, 1388, 1365, 1240, 1175 (broad), 1075 and others
= + 12.7 ° ± 0.5 ° (C = 22 in CHCl₃)

Example 4 tert-Butoxycarbonyl-aspartic acid-β- (tri-tert-butoxysilyl) ester

2.33 g (10 mmol) of Boc-aspartic acid are dissolved in 15 ml of tert-butanol and 4 ml pyridine. 1.3 ml of silicon are added while cooling in an ice bath tetrachloride added. After 12 hours of reaction, the tert-butanol with Toluene evaporated under reduced pressure, the rest in 25 ml of vinegar ester dissolved and with 2% aqueous citric acid, water, then 5% sodium bicarbonate, again with citric acid and then with Washed water. After drying with sodium sulfate, vinegar becomes evaporated with toluene under reduced pressure, the oil obtained dissolved in 10 ml ligroin with 2 ml dicyclohexylamine and in the refrigerator 2 Stored at -20 ° C for days.

The crystals obtained are suction filtered and recri in a little Ligroin installed. 1.6 g of ester are obtained, which are identical to the substance Example 3 is.

The α-isomer, ie. H. tert-butoxycarbonyl Aspartic acid α- (tri-tert-butoxysilyl) ester using the column chromato graphic isolated. Elution with toluene: acetone 4: 1 gives 1.8 g of substance which was found to be identical to that obtained in Example 6 Connection proves.

Example 5 Aspartic acid α and β (tri-tert-butoxysilyl) esters

30 ml of tert-butanol, 1.75 ml of silicon tetrachloride and 3.5 ml of anhydrous Pyridine are stirred together for 2 hours. Then add 1.33 g powdered aspartic acid and the mixture is stirred for a further day. 1.6 ml of pyridine is added and the tert-butanol is added after 2 days evaporated together with toluene under reduced pressure. 20 ml of toluene and 10 ml of ethyl acetate are added to the porridge obtained and the  Washed out the ester phase with 5% sodium carbonate to neutral pH, separated the water and the organic layer with 2% oxalic acid pH 4.5 acidified. The organic phase becomes a gel-like substance precipitated, which was sucked off after 15 min, with water and toluene washed off and then air dried. 1.5 g are obtained amorphous substance consisting of 95% pure α-ester. The 5% rest (the β-isomer) is triggered by acetone: water 4: 1.

Elemental analysis: Molecular weight C₁₆H₃₃NO₇Si · ½ H₂O = 388.5
Ber. C 49.46; H 8.82; N 3.60;
Found: C 49.57; H 8.64; N 3.46.

The organic phase obtained by filtration, which is the β-isomer contains, is separated from the water and in a vacuum rotary evaporator constricted. The precipitated gel-like mass is in 50 ml acetone with 10 ml of water dissolved, filtered through a layer of silica gel 60 (Merck) and concentrated with toluene. The now failed gel-like substance is filtered off, washed with toluene and dried. 1.8 g are obtained pure aspartic acid β- (tri-tert-butoxysilyl) ester, which is identical with the ester obtained according to Example 2.

Example 6 tert-Butoxycarbonyl-aspartic acid α- (tri-tert-butoxysilyl) ester

400 mg of the aspartic acid-α- (tri-tert- butoxysilyl) ester is in 4 ml of tert-butanol and 0.15 mg of triethylamine dissolved and reacted with 0.25 ml of di-tert-butyl dicarbonate. Analogously to Example 3, the ester is isolated as the dicyclohexylamine salt. 590 mg of white crystals are obtained.  

Example 7 tert-Butoxycarbonyl-glutamic acid-β- (tri-tert-butoxysilyl) ester

3 g of glutamic acid are produced using the known method (O. Keller et al., Org. Synthesis, 60, 2145, 1981) with 5 ml of di-tert-butoxydicarbonate Brought reaction and the crude Boc-glutamic acid (a Syrup) is mixed with 4 ml of anhydrous pyridine and 1 day with 25 ml Solution treated according to Example 1. After that, the organic solution (tert-butanol and part of pyridine) with toluene under reduced pressure Pressure is reduced and the thick slurry obtained is dissolved in ethyl acetate, first washed with citric acid and then with water. The solution is concentrated again and the product by means of column chromatography graphie (silica gel, toluene: acetone 6: 1) cleaned. 2.36 g are obtained Boc-glutamic acid di-silicone ester as an oily first fraction, 0.45 g Boc-glutamic acid α- (tri-tert-butyloxylilyl) ester as the second fraction and 6.12 g Boc-glutamic acid β- (tri-tert-butyloxysilyl) ester as the third Fraction. The melting point is 122-123 ° C.

Elemental analysis of the β-ester: molar mass C₃₄H₆₆N₂O₉Si = 674.97
Ber. C 60.50; H 9.86; N 4.15;
Found: C 60.78; H 10.01; N 4.03.

NMR (CDCl₃), δ: 0.84-2.00 (m, 22 H), 1.36 (s, 27 H), 1.44 (s, 9 H), 2.20-2.70 (m, 4 H), 3.00 (m, 2 H) , 4.00 (wide, 1 H), 5.48 (dd, 1 H)
IR (in KBr) cm ^-1 : 3420, 2970, 2940, 2860, 1745, 1715, 1660, 1390, 1365, 1245, 1170 (wide), 1080 (wide) and others

Example 8

1 g of Boc serine hydrate is dissolved with 5 ml of tert-butanol and 1 ml of pyridine. 1.3 g of tri-tert-butoxysilicon chloride are added and the mixture is 2 Days reacted. The product is similar to Example 7  purified by column chromatography. 1.5 g of Boc-serine are obtained (O-tri-tert-butoxysilyl ether) as free acid for peptide synthesis.

Example 9

870 mg Boc-phenylalanyl-DCB derivative (W. Gruszecki et al., Liebigs Ann. Chem., 331, 1988) is dissolved in 10 ml of toluene and 0.6 ml of triethylamine. It is then left with 640 mg of asparagine-β- (tri-tert-butoxysilyl) ester (according to Examples 2 and 5) react for 5 hours. The toluene is under ver evaporated under reduced pressure, the rest mixed with 20 ml of ligroin and filtered through a Schott funnel G-4. The cloudy filtrate becomes a concentrated and dissolved with 5 ml of trifluoroacetic acid: methylene chloride (1: 1). After 10 minutes the acid is evaporated off under reduced pressure, the rest extracted with a little toluene and dried. 410 mg are obtained Phenylalanyl aspartic acid, which is characterized by the thin layer chro matography proves to be identical to the standard.

Example 10

660 mg tert-butoxycarbonyl-aspartic acid-β- (tri-tert-butoxysilyl) - esters according to Example 3 are dissolved in 10 ml of ethyl acetate, with 2% Zi washed tronic acid, then dried with sodium sulfate. To the ester layer, add 300 mg of 1-hydroxybenzotriazole (HOBt), then 214 mg Diclohexylcarbodiimide. After 20 minutes of shaking, 215 mg are added Phenylamine methyl ester hydrochloride and 0.14 ml triethylamine. The reagent mixture is shaken again for 5 hours. After that the precipitated crystals of the diclohexylurea are filtered off, the clear solution with aqueous citric acid, then with 5% sodium Washed bicarbonate and water and dried with sodium sulfate. The protecting groups in the dipeptide thus obtained are as in Example 9 split off. 251 mg of aspartyl phenylalanine methyl ester are obtained, which is identical to aspartame.  

Example 11

203 mg of glucose hydrate are as in Example 8 with tri-tert-butoxy Silicon chloride treated and processed in the usual way. You get 311 mg of glucosyl 6- (tri-tert-butoxysilyl) ether as a clear oil.

Elemental analysis: molar mass C₁₈H₃₈O₉Si = 426.57
Ber. C 50.68; H 8.98;
Found: C 50.88; H 8.82.

Claims (4)

1. silicone ester of the general formula (1) RX-Si (O-R¹) ₃ (1) wherein
R - the residue of an amino acid, a peptide or a sugar of the formula RXH
R¹ - an alkyl of 1 to 4 carbon atoms and
X - an oxygen or sulfur atom
mean. 2. silicone ester of the general formula (1), wherein
R - is a hydrocarbon radical with a maximum of 24 carbon atoms which is optionally substituted by the amino, oxo or thio group and / or interrupted by the oxygen, nitrogen or sulfur atom,
R¹ - and X have the meaning given above. 3. A process for the preparation of substances according to claim 1, characterized characterized in that the organic compound of formula (2) R-X-H (2) where R and X have the meaning given above, with a silicon chloride derivative according to formula (3) (R¹-O) ₃Si-Cl (3) wherein R¹ has the meaning given above, reacts. 4. A process for the preparation of substances according to claim 1, characterized characterized in that the above-mentioned substances R-X-H according Formula (2) dissolved in an alcohol R¹-O-H, where R, R¹ and X are the same Have meaning as in formula (1), in the presence of bases with silicon converts tetrachloride.