GB2232415A - Microbial preparation of benzoic acids - Google Patents

Abstract

Compounds of formula I <IMAGE> wherein R is CH3, OH, F or Cl, are prepared by adding a corresponding compound of formula II <IMAGE> to an anaerobic culture, in a suitable aqueous medium, in the presence of CO2 or a source thereof, of one or more anaerobic bacteria capable of metabolising the formula II compound or phenol and accumulating, respectively, the formula I compound or benzoic acid. The compounds of formula I are useful as intermediates for agrochemicals and pharmaceuticals.

Description

MICROBIAL PREPARATION OF BENZOIC ACIDS This invention relates to a microbial process for the preparation of benzoic acids.

The ability of certain organisms to degrade aromatic compounds under anaerobic conditions is well known, and the general concept of reductive degradation of, say, benzoic acid has been proposed. See Dutton and Evans, Biochem. G.

(1967) 109:5P-6P.

Tschech and Fuchs, Arch. Microbiol. (1987) 148:213-217, disclose the microbial oxidative degradation of phenol, in the absence of molecular oxygen, to CO2 with nitrate as the terminal electron acceptor. Evidence is provided that the first reaction in the anaerobic oxidation is phenol carboxylation, to 4-hydroxybenzoic acid. Various carbon sources were tested in addition to phenol; inter alia, m-cresol and p-cresol were utilised, but o-cresol and catechol were not.

Knoll and Winter, Appl. Microbiol. Biotechnol. (1987) 25:384-391, disclose the anaerobic degradation of phenol in sewage sludge to methane and C02. Based on the different degradation pathways for phenol and benzoic acid proposed by Dutton and Evans, a hypothetical scheme for the degradation is given, in which an initial step comprises the reversible conversion of phenol to benzoic acid (followed by reduction of the aromatic ring).

It has now been found that the anaerobic microbial conversion of phenol to benzoic acid may occur by a mechanism in which the OH- substituted carbon atom in the phenol is in the para position with respect to the COOH-substituted carbon atom in the product. This is evident if the aromatic ring is substituted: according to the present invention, a process for the preparation of a compound of formula I (see below), wherein R is CH3, OH, F or Cl, comprises adding a corresponding compound of formula II to a culture, in a suitable aqueous medium, in the presence of CO2 or a source thereof, of one or more anaerobic bacteria capable of metabolising the formula II compound or phenol and accumulating, respectively, the formula I compound or benzoic acid, without further metabolism.

The process of the invention provides a route for the preparation of, say, m-toluic acid, m-hydroxybenzoic acid, m-fluorobenzoic acid or m-chlorobenzoic acid. These compounds are useful per se, as intermediates in the preparation of, for example, agrochemicals, and in the pharmaceutical and other industries.

The process of the invention also provides compounds which are labelled isotopically in a regiospecific manner, for analytical purposes. The label will usually be deuterium (D) or tritium (T) as one or more of the aromatic hydrogen atoms, and/or 13C or 14C as one or more of the ring carbon atoms or in the carboxyl group.

Studies of the mechanism of the phenol transformation activity show that the H atom at the p-position to the OH substituent in the formula II compound is exchanged specifically, presumably by water protons. The exchange reaction appears to be faster than the formation of product.

According to a second process of the invention, D or T is incorporated from D2 0 or T20 in the medium, to give a compound of formula III (in which R may additionally be H) which may be isolated. However, if the process is allowed to go to completion, using D2O or T2O, the product is a compound of formula IV in which the D or T atom is at the 4-position. The feasibility of such processes has been demonstrated by the conversion of l2,3,4,5,6-d5]phenol to benzoic acid having a 1H substituent at the 4-position whilst retaining the other D substituents on the ring.

Alternatively, if the starting material of formula II is labelled with D or T at the 3, 5 and/or 6-position(s), the process of the invention gives a labelled compound of formula I, specifically a compound of formula IV in which the D or T atom is at the 2, 6 and/or 5-position(s), respectively.

The process of the invention requires CO2 or a source thereof, such as NaHCO3. If the carbon atom of this reactant is labelled isotopically with 13C or 14C, the carbon atom in the COOH group of the product is labelled.

The feasibility of such a conversion has been demonstrated by the conversion of phenol to benzoic acid in the presence of NaH13CO3, which yields benzoic acid with the carboxyl C atom 13C-labelled. Other C-labelled compounds of the invention may be prepared by using a reactant of formula II in which one or more of the ring C atoms is 13C or 14C The following experimental information illustrates how the invention may be practised. In general, the culture conditions will be 25-350C and pH 6.5-8.0.

The phenol-transforming activity can be grown anaerobically in FW-salts medium (composition shown in Table 1) plus (a) 0.5-5.0 g.1-1 yeast extract; (b) 1.5 g.1-1 yeast extract and 0.5 g-1 peptone; (c) 1.5 g.1-1 yeast extract and 0.5 g.l 1 formate; (d) 1.5 g.l 1 yeast extract and 0.4-4.0 g.l-1 lactate; (e) 1.5 g.l-1 yeast extract and 0.5 g.l-1 acetate; (f) yeast extract and any mixture of peptone, formate, lactate and acetate. It is also possible to use MBM medium (Table 4).

-1 In all cases phenol was present at 0.5 g.l and the cultures were grown at pH 7.0 and 300C.

The phenol-transforming activity can be grown in continuous culture at 300C in a medium containing FW-salts, 0.5 g.1-1 of yeast extract and peptone and 5 mM formate and lactate with 1.0 g.1-1 phenol at pH 7-8. The maximum dilution rate was 0.016 h-1 giving a specific productivity (qP) of 0.05 g benzoic acid formed. (g of cells) -1 l.h l. To preserve anaerobic conditions, the fermenter was sparged with a gas mixture containing 80% N2: 10% H2: 10t C02 at 0.05 vol. of gas.(vol. of fermenter broth) l.min and the medium reservoir was sparged with N2.

All anaerobic manipulations were carried out in an anaerobic cabinet (Don Whitley Scientific Ltd.; either Mk 2 or Mk 3). The Mk 2 cabinet is supplied with a gas mixture of about 80% N2, 10% CO2 and 10% H2 and has been found to contain a gas mixture of about 85% N2, 10% CO2 and 5% H2 in use. The Mk 3 cabinet contains an atmosphere of about 96% N2, 2% CO2 and 2% H2.

The FW-salts medium was degassed with N2 for 30 min on the bench and then transferred to the anaerobic cabinet where it was dispensed into bottles or tubes as required.

The bottles or tubes were sealed with butyl rubber stoppers and Al crimped closures, sterilised at 1200C for 15 min and then returned to the anaerobic cabinet, where additions were made as required from sterilised containers by means of sterile syringes and needles.

The aromatic substrates and products were determined by capillary gas chromatography (GC). A 0.3 ml culture sample was acidified with 1 drop of 5 M HCl, centrifuged to remove cells and debris and then a sample of the supernatant was injected (0.5 Fl; injection temp. 1350C; split injection mode, ratio 20:1) into a Hewlett-Packard GC model 5790A fitted with an HP-5 (cross-linked 5% Ph Me silicone gum) capillary column 25 m long, 0.32 mm I.D.

and 1.05 Am film thickness. The carrier gas was He (1 ml.min l) and peaks were detected by a flame ionisation detector set at 3000C. The oven temp. was held at 1300C for 8 min, programmed to 2500C at a rate of 120C.min and finally held at 2500C for a further 5-10 min.

A list of GC retention times is given in Table 3.

Samples from cultures (typically 5 ml) were spun down on a bench centrifuge for 5 min. The supernatants were acidified with concentrated HCl and then extracted with 3 volumes of diethyl ether. The ether extracts were dried through phase-separating paper and concentrated with a stream of N2. The residue was redissolved in ether and an aliquot (usually 1 Fl) was injected into a Finnigan 4500 combined GC/MS quadruple instrument in the electron impact (EI) mode. The injector was from a Varian 4700 GC and operated at 150-2000C in the split mode (20:1). The capillary GC column used was a Chrompak CP-SIL-8CB, 25 m x 0.32 mm, thick film; carrier gas, He at 1 ml.min Data from the MS were collected using an Incos data system, scanning at 1 sec intervals.Peaks were compared with standard EI-MS spectra from an NBS library containing 38,000 spectra.

In the anaerobic cabinet, a 125 ml glass bottle (Hypovial, Pierce & Warriner) containing 80 ml of N2-degassed FW-salts medium was charged with a mixture of anaerobic sediments (5-10 g each), collected from Sittingbourne sewage digester, a pond on the Isle of Grain, Betteshanger coal mine (4 samples from different locations mixed together) and Shell Haven oil refinery (6 samples from different pond and ditch sediments mixed -1 together). Phenol was added to 0.2 g.l 1 and the pH was adjusted to 7.0. The bottle was sealed with a butyl rubber stopper and incubated at 300C.

The sediment samples were collected by filling the vessel as completely as possible with the wet sediment, to exclude as much air as possible, before sealing with either a metal screw top with rubber liner (25 ml glass bottles) or with butyl rubber stoppers (Belco) held on with Al crimped closures (125 ml Hypovials).

After 83 days, no phenol had been used and so vitamins (Table 2), 0.1 g.l 1 yeast extract and 0.1 g.1-1 peptone together with two more mixed sediment samples were added; these were collected from Synthetic Chemicals Ltd., Wolverhampton (46 samples from different locations mixed together) and Ward-Blenkinsop, Runcorn (50 samples from different locations mixed together).

Incubation at 300C resulted in phenol metabolism as judged by capillary GC (see above). This activity was maintained in the culture on further addition of phenol, yeast extract and peptone. A product was formed from the phenol, which was identified by GC retention time and GC/MS as benzoic acid. The product was extracted from the acidified culture with diethyl ether and the ether extract was dried by filtration through phase-separating paper.

After concentration of the extract, the residue was reacted with ethereal diazomethane for about 5 sec at 200C, and then the solution was taken to dryness with a stream of N2. The presence of methyl benzoate in the methylated extract was confirmed by GC retention time and by GC/MS. Quantitative GC analysis showed that there was a stoichiometric conversion of phenol to benzoic acid.

The mixed culture can be subcultured repeatedly by anaerobic incubation at 300C in a medium containing -l FW-salts, 0.5 g.l 1 of yeast extract and peptone and 5 mM -1 formate and lactate with 0.5 g.l 1 phenol at pH 7.0.

The mixed culture has been deposited at the National Collections of Industrial and Marine Bacteria Ltd.

(NCIMB), Aberdeen, Scotland. The deposit date was 21st April 1989 and the accession number is NCIMB 40132.

Example 1 m-Fluorobenzoic Acid To 8 ml of anaerobic medium containing FW-Salts, 0.5 1 of yeast extract and peptone and 5 mM formate and lactate in an 18 x 150 mm culture tube (Belco) were added 0.2 g.l 1 phenol and 2 ml of an active culture growing on the same medium as inoculum. The tubes were sealed with butyl rubber stoppers and Al crimped closures and incubated at pH 7.0 and 300C. After several days, when GC analysis showed the formation of benzoic acid, 0.2 g.l 1 of o-fluorophenol from a 1% (w/v) aqueous solution was added, and incubation was continued. After about 1 week, and subsequently, samples were analysed by GC.

m-Fluorobenzoic acid was identified by comparison of its GC retention time with that for an authentic standard and by GC/MS. Ether extraction from an acidified culture sample and methylation by ethereal diazomethane (see above) showed the presence of methyl m-fluorobenzoate by GC retention time and GC/MS, confirming the original presence of m-fluorobenzoic acid.

The formation of m-fluorobenzoic acid was confirmed 19 also by F-NMR (spectra acquired on aqueous samples using a Bruker WM-250 spectrometer operating at 235 MHz and 300C; chemical shifts related to CFC13 in CDCl3 as reference for zero ppm; D2O was added to the sample solution to provide a lock signal) directly on a sample of the supernatant from the o-fluorophenol culture. The chemical shift of the product coincided with that for authentic m-fluorobenzoic acid in aqueous solution at pH 7 (-115.8 ppm) but not with those for o- and p-fluorobenzoic acids (-117.9 and -112.2 ppm, respectively).

Example 2 m-Chlorobenzoic Acid The procedure of Example 1 was repeated, but substituting o-chlorophenol for o-fluorophenol. GC retention time comparison and GC/MS identified the product as m-chlorobenzoic acid.

Example 3 m-Hydroxybenzoic Acid The procedure of Example 1 was repeated, but substituting 1,2-benzenediol (catechol) for o-fluorophenol. GC retention time comparison and GC/MS identified the product as m-hydroxybenzoic acid. After methylation (see Example 1 above) GC and GC/MS confirmed the presence of methyl m-hydroxybenzoate.

Example 4 m-Toluic Acid The procedure of Example 1 was repeated, but substituting o-methylphenol (o-cresol) for o-fluorophenol.

GC retention time comparison and GC/MS identified the product as m-toluic acid. After methylation (see Example 1 above) GC and GC/MS confirmed the presence of methyl m-toluate.

The following Example illustrates the second aspect of the invention. 13C-NMR spectra were obtained using either a Nicolet QE-300 spectrometer operating at 75 MHz and ambient temperature (for d4-benzoic acid spectra in CDCl3 with D2 0 added to provide a lock signal) or a Bruker WM-250 spectrometer operating at 62.5 MHz and 300C (for the d4-phenol spectra in H2O with D2O added to provide a lock signal).

Example 5 To 50 ml of anaerobic medium containing sterile FW-salts, 0.5 g.1-1 of yeast extract and peptone and 5 mM formate and lactate, in a 125 ml glass hypovial sealed with a butyl rubber stopper and an Al crimped closure, was added 1.0 ml of freshly-prepared aqueous 5% (w/v) [d6]phenol (MSD Isotopes, 98.7 atom % D; the OD exchanges immediately with H2 0 in the solution giving [2,3,4,5,6-d5]phenol). The inoculum was prepared by spinning down in a sterile tube a 50 ml culture which had been growing actively in the presence of unlabelled phenol. The tube was transferred to the anaerobic cabinet where the supernatant was discarded. The resulting pellet of cells, containing very little of the original culture broth, was resuspended in some of the fresh culture medium and transferred back into the bottle, the pH was adjusted to about 7.4 with 2 ml of sterile 1.5 M NaHCO3, and the bottle was incubated at 300C. Samples were checked by GC for benzoic acid formation and then, after ether extraction, were analysed by GC/MS in the chemical ionisation mode (CI) using methane as the reactant gas.

Both the phenol and the benzoic acid showed (M+H) ions corresponding to 4 D atoms per molecule. (A zero time sample confirmed that the phenol carried 5 D atoms at the start).

When most of the phenol had been transformed into benzoic acid, a 5 ml samples of the culture was spun down and the supernatant was extracted into ether, dried over anhydrous MgSO4 and filtered, and the filtrate was evaporated with a stream of N2. The residue was dissolved 13 in CDCl3 for C-NMR analysis. A large singlet was observed at 133.46 ppm corresponding to the C-atom in benzoic acid carrying a 1H substituent at position 4 in the ring; the signals corresponding to the pairs of C atoms at C-2 and C-3 were observed at 129.38 and 127.96 ppm, respectively as small equal-sized triplets, showing that each was still coupled to a D-atom.

The culture bottle from above was reinoculated with a further 1.0 ml aliquot of freshly-prepared aqueous 5% (w/v) td6]phenol. After a further 14 days at 300C, a 2 ml sample was spun down and the supernatant was analysed by C-NMR. A singlet was observed at 123.3 ppm corresponding to C-4 of phenol carrying a 1H substituent.

The phenol was shown to have 4 D-atoms per molecule at this stage by a separate GC/MS determination in the CI mode.

Table 1. Composition of FW-salts Component g.1-1 mM KH2PO4 4.08 30 NH4C1 1.07 20 MgSO4.7H2O 0.246 1.0 NaCl 0.058 1.0 CaCl2.2H2O 0.147 0.1 Resazurin 0.001 Trace element solution 2 ml.l-1 Adjust pH to 7.0 with KOH COMPOSITION OF TRACE ELEMENT SOLUTION Componet g.l-1 FeCl3.6H2O2.0 CoCl2.6H2O 1.36 MnCl2.4H2O 0.6 ZnCl2 0.4 NiCl2 0.2 Na2MoO4.2H2O 0.2 CuCl2 0.1 H3BO3 0.08 Na2Se)3 0.016 Na2Wo4.2H2O 0.008 1 M HCl 200 ml. 1-1 Table 2. Composition of vitamins solution Component mg.l-1 Pyridoxine.HCl 10 Riboflavin 5 Thiamin 5 Nicotinic acid 5 Pantothenic acid 5 p-Aminobenzoic acid 5 Thiooctic acid 5 Biotin 3 Folic acid 2 Vitamin B12 0.12 Used at 0..5 ml.1-1 Table 3.Retention times on capillary GC Compound Retention tim (min) o-Flucrcphenol 2.23 Phenol 2.98 o-Chlorophenol 3.40 ocresol 3.99 Methyl m-fluorobenzoate 4.52 methyl benzoate 5.02 m-Fluorobenzoic acid 6.07 Benzoic acid 6.1 Catechol 7.1 Methyl m-toluate 7.9 m-Toluic acid 3.32 m-Chlorobenzoic 11.2 Methyl m-hydroxybenzoate 13.0 m-Hydroxybenzoic 13.8 Table 4. Composition of MBM medium Component g.l-1 NaHCO3 4.0 Na formate 2.0 Na acetate 1.0 Yeast extract 1.0 KH2PO4 0.5 NH4Cl 0.4 MgSO4.7H2O 0.4 NaCl 0.4 Cysteine.HCl 0.3 Na2S 0.3 CaCl2.2H2O 0.05 FeSO4.7H2O 0.002 Fesazurin 0.001 Sludge fluid 50 ml.1-1 Fatty acid mixture 20 ml.1-1 Trace elements solution 1 ml.1-1 Adjust pH to 7.0 with NaOH COMPOSITION OF TRACE ELEMENT SOLUTION Component g.l-1 H3BO3 0.3 CoCl2.6H2O 0.2 ZnSO4.7H2O 0.1 MnCl2.4H2O 0.03 Na2MoO4.2H2O 0.03 NiCl2.H2O 0.02 CuCl2.2H2O 0.01 COMPOSTION OF FATTY ACID MIXTURE Component g.20ml-1 Valeric acid 0.5 Isovaleric acid 0.5 2-Methylbutyric acid 0.5 Isobutyric acid 0.5 Adjust pH to 7.0 with NaOH

Claims (6)

1. CLAIMS 1. A process for the preparation of a compound of formula I

   wherein R is CH3, OH, F or Cl, which comprises adding a corresponding compound cf formula II

   to an anaerobic culture, in a suitable aqueous medium, in the presence of CO2 or a source thereof, cf one or more anaerobic bacteria capable of metabolising the formula II compound cr phenol and accumulating, respectively, the formula I compound or benzoic acids
2. 2. A process according to claim 1, in which cne or mcre of the C atoms in the ring or in the COOH group, and/or one or more of the aromatic H atoms in the compound of formula I, is labelled isotopically.
3. 3. A process for the preparation o a compound of formula TIT

   wherein R is H, CH3, OH, F or C1 and D/T is deuterium (D) or tritium (T), which comprises adding a corresponding compound of formula II (see claim 1) to an anaerobic culture, in a suitable medium containing D2O or T20, of one or more anaerobic bacteria capable of metabolising the formula II compound and accumulating the formula III compound.
4. 4. A process according to claim 3, which is conducted in the presence of CO2 or a source thereof.
5. 5. A process according to any of claims 1, 2 and 4, which is ccnducted in the presence of NaHCO3.
6. 6. A process according to any preceding claim, in which the one or more anaerobic bacteria are as available under the deposit NCIMB 40132.