# Patent

## Title
Epoxidation using peroxygenase

## Abstract

The invention relates to enzymatic methods for epoxidation of a non-cyclic aliphatic alkene, or a terpene.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. application Ser. No. 15/250,290 filed on Aug. 29, 2016, now U.S. Pat. No. 9,663,806, which is a divisional of U.S. application Ser. No. 14/382,957 filed on Sep. 4, 2014, now U.S. Pat. No. 9,458,478, which is a 35 U.S.C. 371 national application of international application no. PCT/EP2013/056326 filed on Mar. 25, 2013, which claims priority or the benefit under 35 U.S.C. 119 of European application nos. 12162791.3 and 12165214.3 filed on Mar. 31, 2012 and Apr. 23, 2012, respectively, and U.S. provisional application Nos. 61/622,686 and 61/636,956 filed on Apr. 11, 2012 and Apr. 23, 2012, respectively. The content of these applications is fully incorporated herein by reference.


CROSS-REFERENCE TO A SEQUENCE LISTING
This application contains a Sequence Listing in computer readable form, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to use of peroxygenases for epoxidation of non-cyclic aliphatic alkenes, or terpenes.
Background
A peroxygenase denoted AaP from the agaric basidiomycete strain Agrocybe aegerita (strain TM-A1) was found to oxidize aryl alcohols and aldehydes. The AaP peroxygenase was purified from A. aegerita TM A1 by several steps of ion chromatography, the molecular weight was determined by SDS-PAGE and the N-terminal 14 amino acid sequence was determined after 2-D electrophoresis but the encoding gene was not isolated (Ullrich et al., 2004, Appl. Env. Microbiol. 70(8): 4575-4581).
WO 2006/034702 discloses methods for the enzymatic hydroxylation of non-activated hydrocarbons, such as, naphtalene, toluol and cyclohexane, using the AaP peroxygenase enzyme of Agrocybe aegerita TM A1. This is also described in Ullrich and Hofrichter, 2005, FEBS Letters 579: 6247-6250.
WO 2008/119780 discloses eight different peroxygenases from Agrocybe aegerita, Coprinopsis cinerea, Laccaria bicolor and Coprinus radians. 
DE 103 32 065 A1 discloses methods for the enzymatic preparation of acids from alcohols through the intermediary formation of aldehydes by using the AaP peroxygenase enzyme of Agrocybe aegerita TM A1.
A method was reported for the rapid and selective spectrophotometric direct detection of aromatic hydroxylation by the AaP peroxygenase (Kluge et al., 2007, Appl. Microbiol. Biotechnol. 75: 1473-1478).
It is well-known that a direct regioselective introduction of oxygen functions (oxygenation) into organic molecules constitutes a problem in chemical synthesis. The products may be used as important intermediates in a wide variety of different syntheses.
It is known that an intracellular enzyme, methane monooxygenase (MMO, EC 14.13.25), oxygenates/hydroxylates the terminal carbon of some hydrocarbons. The MMO enzyme consists of several protein components and is solely formed by methylotrophic bacteria (e.g. Methylococcus capsulatus); it requires complex electron donors such as NADH or NADPH, auxiliary proteins (flavin reductases, regulator protein) and molecular oxygen (O2). The natural substrate of MMO is methane, which is oxidized to methanol. As a particularly unspecific biocatalyst, MMO oxygenates/hydroxylates, as well as methane, a series of further substrates such as n-alkanes and their derivatives, cycloalkanes, aromatics, carbon monoxide and heterocycles. Utilization of the enzyme in biotechnology is currently not possible, since it is difficult to isolate, like most intracellular enzymes, it is of low stability, and the cosubstrates required are relatively expensive.
SUMMARY OF THE INVENTION
In a first aspect, the inventors of the present invention have provided an enzymatic method for producing an epoxide, comprising contacting a non-cyclic aliphatic alkene, or a terpene, with hydrogen peroxide and a peroxygenase; wherein the peroxygenase comprises an amino acid sequence which has at least 60% identity to SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In an embodiment, the amino acid sequence comprises the motif: E-H-D-[G,A]-S-[L,I]-S-R (SEQ ID NO: 21).
Definitions
Peroxygenase activity: The term “peroxygenase activity” means an “unspecific peroxygenase” activity according to EC 1.11.2.1, that catalyzes insertion of an oxygen atom from H2O2 into a variety of substrates, such as nitrobenzodioxole. For purposes of the present invention, peroxygenase activity is determined according to the procedure described in Poraj-Kobielska et al., 2012, “A spectrophotometric assay for the detection of fungal peroxygenases”, Analytical Biochemistry 421(1): 327-329.
The peroxygenase of the present invention has at least 20%, preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, even more preferably at least 90%, most preferably at least 95%, and even most preferably at least 100% of the peroxygenase activity of the mature polypeptide of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20.
Mature polypeptide: The term “mature polypeptide” is defined herein as a polypeptide having peroxygenase activity that is in its final form following translation and any post-translational modifications, such as N-terminal processing, C-terminal truncation, glycosylation, phosphorylation, etc. In a preferred aspect, the mature polypeptide has the amino acid sequence shown in positions 1 to 328 of SEQ ID NO:1 based on the N-terminal peptide sequencing data (Ullrich et al., 2004, Appl. Env. Microbiol. 70(8): 4575-4581), elucidating the start of the mature protein of AaP peroxygenase enzyme.
Identity: The relatedness between two amino acid sequences or between two nucleotide sequences is described by the parameter “identity”.
For purposes of the present invention, the degree of identity between two amino acid sequences is determined using the Needleman-Wunsch algorithm (Needleman and Wunsch, 1970, J. Mol. Biol. 48: 443-453) as implemented in the Needle program of the EMBOSS package (EMBOSS: The European Molecular Biology Open Software Suite, Rice et al., 2000, Trends in Genetics 16: 276-277; emboss.org), preferably version 3.0.0 or later. The optional parameters used are gap open penalty of 10, gap extension penalty of 0.5, and the EBLOSUM62 (EMBOSS version of BLOSUM62) substitution matrix. The output of Needle labeled “longest identity” (obtained using the -nobrief option) is used as the percent identity and is calculated as follows:

(Identical Residues×100)/(Length of Alignment−Total Number of Gaps in Alignment)

For purposes of the present invention, the degree of identity between two deoxyribonucleotide sequences is determined using the Needleman-Wunsch algorithm (Needleman and Wunsch, 1970, supra) as implemented in the Needle program of the EMBOSS package (EMBOSS: The European Molecular Biology Open Software Suite, Rice et al., 2000, supra; emboss.org), preferably version 3.0.0 or later. The optional parameters used are gap open penalty of 10, gap extension penalty of 0.5, and the EDNAFULL (EMBOSS version of NCBI NUC4.4) substitution matrix. The output of Needle labeled “longest identity” (obtained using the -nobrief option) is used as the percent identity and is calculated as follows:

(Identical Deoxyribonucleotides×100)/(Length of Alignment−Total Number of Gaps in Alignment).

Modification: The term “modification” means herein any chemical modification of the polypeptide consisting of the mature polypeptide of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20; or a homologous sequence thereof; as well as genetic manipulation of the DNA encoding such a polypeptide. The modification can be a substitution, a deletion and/or an insertion of one or more (several) amino acids as well as replacements of one or more (several) amino acid side chains.


DETAILED DESCRIPTION OF THE INVENTION
Peroxygenase
The present invention relates to methods for epoxidation using a polypeptide, which is preferably recombinantly produced, having peroxygenase activity (referenced as “peroxygenase”), which comprises or consists of an amino acid sequence having at least 60% identity, preferably at least 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% identity to the polypeptide of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20; preferably SEQ ID NO: 1.
In a preferred embodiment, the peroxygenase comprises an amino acid sequence represented by the motif: E-H-D-[G,A]-S-[L,I]-S-R (SEQ ID NO: 21).
In yet another embodiment, the polypeptide of the first aspect comprises or consists of the amino acid sequence of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20; preferably SEQ ID NO: 1; or a fragment thereof having peroxygenase activity; preferably the polypeptide comprises or consists of the mature polypeptide of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20; preferably SEQ ID NO: 1.
Preferably, amino acid changes are of a minor nature, that is conservative amino acid substitutions or insertions that do not significantly affect the folding and/or activity of the protein; small deletions, typically of one to about 30 amino acids; small amino- or carboxyl-terminal extensions, such as an amino-terminal methionine residue; a small linker peptide of up to about 20-25 residues; or a small extension that facilitates purification by changing net charge or another function, such as a poly-histidine tract, an antigenic epitope or a binding domain.
Examples of conservative substitutions are within the group of basic amino acids (arginine, lysine and histidine), acidic amino acids (glutamic acid and aspartic acid), polar amino acids (glutamine and asparagine), hydrophobic amino acids (leucine, isoleucine and valine), aromatic amino acids (phenylalanine, tryptophan and tyrosine), and small amino acids (glycine, alanine, serine, threonine and methionine). Amino acid substitutions that do not generally alter specific activity are known in the art and are described, for example, by H. Neurath and R. L. Hill, 1979, In, The Proteins, Academic Press, New York. The most commonly occurring exchanges are Ala/Ser, Val/Ile, Asp/Glu, Thr/Ser, Ala/Gly, Ala/Thr, Ser/Asn, Ala/Val, Ser/Gly, Tyr/Phe, Ala/Pro, Lys/Arg, Asp/Asn, Leu/Ile, Leu/Val, Ala/Glu, and Asp/Gly.
In addition to the 20 standard amino acids, non-standard amino acids (such as 4-hydroxyproline, 6-N-methyl lysine, 2-aminoisobutyric acid, isovaline, and alpha-methyl serine) may be substituted for amino acid residues of a wild-type polypeptide. A limited number of non-conservative amino acids, amino acids that are not encoded by the genetic code, and unnatural amino acids may be substituted for amino acid residues. “Unnatural amino acids” have been modified after protein synthesis, and/or have a chemical structure in their side chain(s) different from that of the standard amino acids. Unnatural amino acids can be chemically synthesized, and preferably, are commercially available, and include pipecolic acid, thiazolidine carboxylic acid, dehydroproline, 3- and 4-methylproline, and 3,3-dimethylproline.
Alternatively, the amino acid changes are of such a nature that the physico-chemical properties of the polypeptides are altered. For example, amino acid changes may improve the thermal stability of the polypeptide, alter the substrate specificity, change the pH optimum, and the like.
Essential amino acids in the parent polypeptide can be identified according to procedures known in the art, such as site-directed mutagenesis or alanine-scanning mutagenesis (Cunningham and Wells, 1989, Science 244: 1081-1085). In the latter technique, single alanine mutations are introduced at every residue in the molecule, and the resultant mutant molecules are tested for biological activity (i.e., peroxygenase activity) to identify amino acid residues that are critical to the activity of the molecule. See also, Hilton et al., 1996, J. Biol. Chem. 271: 4699-4708. The active site of the enzyme or other biological interaction can also be determined by physical analysis of structure, as determined by such techniques as nuclear magnetic resonance, crystallography, electron diffraction, or photoaffinity labeling, in conjunction with mutation of putative contact site amino acids. See, for example, de Vos et al., 1992, Science 255: 306-312; Smith et al., 1992, J. Mol. Biol. 224: 899-904; Wlodaver et al., 1992, FEBS Lett. 309: 59-64. The identities of essential amino acids can also be inferred from analysis of identities with polypeptides that are related to a polypeptide according to the invention.
Single or multiple amino acid substitutions, deletions, and/or insertions can be made and tested using known methods of mutagenesis, recombination, and/or shuffling, followed by a relevant screening procedure, such as those disclosed by Reidhaar-Olson and Sauer, 1988, Science 241: 53-57; Bowie and Sauer, 1989, Proc. Natl. Acad. Sci. USA 86: 2152-2156; WO 95/17413; or WO 95/22625. Other methods that can be used include error-prone PCR, phage display (e.g., Lowman et al., 1991, Biochem. 30: 10832-10837; U.S. Pat. No. 5,223,409; WO 92/06204), and region-directed mutagenesis (Derbyshire et al., 1986, Gene 46: 145; Ner et al., 1988, DNA 7: 127).
Mutagenesis/shuffling methods can be combined with high-throughput, automated screening methods to detect activity of cloned, mutagenized polypeptides expressed by host cells (Ness et al., 1999, Nature Biotechnology 17: 893-896). Mutagenized DNA molecules that encode active polypeptides can be recovered from the host cells and rapidly sequenced using standard methods in the art. These methods allow the rapid determination of the importance of individual amino acid residues in a polypeptide of interest, and can be applied to polypeptides of unknown structure.
The total number of amino acid substitutions, deletions and/or insertions of the mature polypeptide of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20; preferably SEQ ID NO: 1; is 10, preferably 9, more preferably 8, more preferably 7, more preferably at most 6, more preferably 5, more preferably 4, even more preferably 3, most preferably 2, and even most preferably 1.
Hydrogen Peroxide
The hydrogen peroxide required by the peroxygenase may be provided as an aqueous solution of hydrogen peroxide or a hydrogen peroxide precursor for in situ production of hydrogen peroxide. Any solid entity which liberates upon dissolution a peroxide, which is useable by peroxygenase, can serve as a source of hydrogen peroxide. Compounds which yield hydrogen peroxide upon dissolution in water or an appropriate aqueous based medium include but are not limited to metal peroxides, percarbonates, persulphates, perphosphates, peroxyacids, alkyperoxides, acylperoxides, peroxyesters, urea peroxide, perborates and peroxycarboxylic acids or salts thereof.
Another source of hydrogen peroxide is a hydrogen peroxide generating enzyme system, such as an oxidase together with a substrate for the oxidase. Examples of combinations of oxidase and substrate comprise, but are not limited to, amino acid oxidase (see e.g. U.S. Pat. No. 6,248,575) and a suitable amino acid, glucose oxidase (see e.g. WO 95/29996) and glucose, lactate oxidase and lactate, galactose oxidase (see e.g. WO 00/50606) and galactose, and aldose oxidase (see e.g. WO 99/31990) and a suitable aldose.
By studying EC 1.1.3._, EC 1.2.3._, EC 1.4.3._, and EC 1.5.3.— or similar classes (under the International Union of Biochemistry), other examples of such combinations of oxidases and substrates are easily recognized by one skilled in the art.
Alternative oxidants which may be applied for peroxygenases may be oxygen combined with a suitable hydrogen donor like ascorbic acid, dehydroascorbic acid, dihydroxyfumaric acid or cysteine. An example of such oxygen hydrogen donor system is described by Pasta et al., 1999, Biotechnology & Bioengineering 62(4): 489-493.
Hydrogen peroxide or a source of hydrogen peroxide may be added at the beginning of or during the method of the invention, e.g. as one or more separate additions of hydrogen peroxide; or continously as fed-batch addition. Typical amounts of hydrogen peroxide correspond to levels of from 0.001 mM to 25 mM, preferably to levels of from 0.005 mM to 5 mM, and particularly to levels of from 0.01 to 1 mM or 0.02 to 2 mM hydrogen peroxide. Hydrogen peroxide may also be used in an amount corresponding to levels of from 0.1 mM to 25 mM, preferably to levels of from 0.5 mM to 15 mM, more preferably to levels of from 1 mM to 10 mM, and most preferably to levels of from 2 mM to 8 mM hydrogen peroxide.
Surfactants
The method of the invention may include application of a surfactant (for example, as part of a detergent formulation or as a wetting agent). Surfactants suitable for being applied may be non-ionic (including semi-polar), anionic, cationic and/or zwitterionic; preferably the surfactant is anionic (such as linear alkylbenzenesulfonate, alpha-olefinsulfonate, alkyl sulfate (fatty alcohol sulfate), alcohol ethoxysulfate, secondary alkanesulfonate, alpha-sulfo fatty acid methyl ester, alkyl- or alkenylsuccinic acid or soap) or non-ionic (such as alcohol ethoxylate, nonylphenol ethoxylate, alkylpolyglycoside, alkyldimethylamineoxide, ethoxylated fatty acid monoethanolamide, fatty acid monoethanolamide, polyhydroxy alkyl fatty acid amide, or N-acyl N-alkyl derivatives of glucosamine (“glucamides”)), or a mixture thereof.
When included in the method of the invention, the concentration of the surfactant will usually be from about 0.01% to about 10%, preferably about 0.05% to about 5%, and more preferably about 0.1% to about 1% by weight.
Aliphatic Alkene
The aliphatic alkene (unsaturated aliphatic hydrocarbon), which is epoxidized in the method of the invention, is a non-cyclic aliphatic alkene, which is linear or branched; and substituted or unsubstituted. Preferably, the aliphatic alkene is unsubstituted. Branched alkenes correspond to isomers of linear alkenes.
In an embodiment, the non-cyclic aliphatic alkene has at least three carbons. In another embodiment, the aliphatic alkene has a carbon-carbon double bond (an unsaturated carbon) at one end.
Preferably, the aliphatic alkene is propene, butene, pentene, hexene, heptene, octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene or hexadecene, or isomers thereof. More preferably, the aliphatic akene is propene, 1-butene, 1-pentene, 1-hexene, 2-hexene, 3-hexene, 1-heptene, 1-octene, 2-methyl-2-butene, 2,3-dimethyl-2-butene, cis/trans-2-butene, isobutene, 1,3-butadiene, and isoprene; or isomers thereof.
When the aliphatic alkenes are substituted (functional groups attached), the preferred substituents are halogen, hydroxyl, carboxyl, amino, nitro, cyano, thiol, sulphonyl, formyl, acetyl, methoxy, ethoxy, carbamoyl and sulfamoyl; more preferred substituents are chloro, hydroxyl, carboxyl and sulphonyl; and most preferred substituents are chloro and carboxyl.
The aliphatic alkenes may be substituted by up to 10 substituents, up to 8 substituents, up to 6 substituents, up to 4 substituents, up to 2 substituents, or by up to one substituent.
Terpene
The terpenes, which are epoxidized according to the invention, include isoprene, and compounds having multiples of the isoprene structure. The terpenes of the invention also include terpenoids.
Terpenes can be subdivided in monoterpenes (two isoprene units), sesquiterpenes (three isoprene units), diterpenes (four isoprene units), triterpenes (six isoprene units), tetraterpenes (eight isoprene units) etc. Terpenes can be monocyclic, bicyclic, tricyclic, etc. Examples of monoterpenes include geraniol (rose oil) and monocyclic monoterpenes, such as (−)-menthol (peppermint oil), R-(+)-carvone (caroway oil), S-(−)-carvone (spearmint oil), R-(+)-limonene (orange oil), and S-(−)-limonene (pine oil smell).
Preferably the terpene of the invention is isoprene or a monoterpene; more preferably the terpene is a cyclic terpene, such as a monocyclic monoterpene, such as limonene.
Terpenes and cyclic terpenes like limonene are found broadly in nature. Limonene is the most abundant common naturally occurring terpene—produced by more than 300 plants and is a major component in citrus peel oil. Epoxidation of limonene is of particular relevance since it forms the basis for the synthesis of fragrances and drugs. Peroxygenases epoxidize limonene both in the ring position and in the side chain—with dominating preference for the ring position (see Example 1).
Methods and Uses
The present invention provides a method for producing an epoxide from a non-cyclic aliphatic alkene, or a terpene (a method for epoxidation of a non-cyclic aliphatic alkene or a terpene), comprising contacting the aliphatic alkene, or terpene, with a peroxygenase and hydrogen peroxide. Thus, the invention provides a method for converting a non-cyclic aliphatic alkene, or terpene, to an epoxide, by oxidation of the aliphatic alkene or terpene at a carbon-carbon double bond.
The aliphatic alkene includes at least three carbons. Preferably, the aliphatic alkene has a carbon-carbon double bond (an unsaturated carbon) at one end.
Accordingly, in a first aspect, the present invention provides a method for producing an epoxide, comprising contacting a non-cyclic aliphatic alkene, or terpene, with hydrogen peroxide and a peroxygenase; wherein the peroxygenase comprises an amino acid sequence which has at least 60% identity to SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. The aliphatic alkene may be substituted or unsubstituted, linear or branched.
In an embodiment, the amino acid sequence comprises the motif: E-H-D-[G,A]-S-[L,I]-S-R (SEQ ID NO: 21).
In an embodiment, the peroxygenase comprises or consists of an amino acid sequence having at least 65% identity, preferably at least 70% identity, more preferably at least 75% identity, more preferably at least 80% identity, more preferably at least 85% identity, most preferably at least 90% identity, and in particular at least 95% identity to the amino acid sequence of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20; preferably SEQ ID NO: 1. In a preferred embodiment, the peroxygenase comprises or consists of the amino acid sequence of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20; preferably SEQ ID NO: 1; or a fragment thereof having peroxygenase activity.
In an embodiment, the terpene is isoprene or a monoterpene; preferably the terpene is a cyclic terpene, such as a monocyclic monoterpene, such as limonene.
In another embodiment, the aliphatic alkene has one or more substituents selected from the group consisting of halogen, hydroxyl, carboxyl, amino, nitro, cyano, thiol, sulphonyl, formyl, acetyl, methoxy, ethoxy, carbamoyl and sulfamoyl. Preferably, the substituent(s) are selected from the group consisting of chloro, hydroxyl, carboxyl and sulphonyl; in particular, chloro and carboxyl.
In another embodiment, the aliphatic alkene consists of at least three carbons, and has a carbon-carbon double bond at one end.
In another embodiment, the aliphatic alkene is propene, butene, pentene, hexene, heptene, octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene or hexadecene, or isomers thereof. In a more preferred embodiment, the aliphatic alkene is propene, 1-butene, 1-pentene, 1-hexene, 2-hexene, 3-hexene, 1-heptene, 1-octene, 2-methyl-2-butene, 2,3-dimethyl-2-butene, cis/trans-2-butene, isobutene, 1,3-butadiene, and isoprene; or isomers thereof.
In another embodiment, the aliphatic alkene is unsubstituted.
In another embodiment, the aliphatic alkene is linear.
Preferred epoxides, which can be produced by the method of the invention include, but are not limited to, propylene oxide (1,2-epoxypropane) and epoxy terpenes (including epoxy terpenoids), such as limonene oxide; and 2-methyloxirane, 2-ethyloxirane, 2-propyloxirane, 2-butyloxirane, 2-pentyloxirane, 2-hexyloxirane, 2,2,3-trimethyloxirane, 2,2,3,3-tetramethyloxirane, (2S,3S)-2,3-dimethyloxirane, (2R,3S)-2,3-Dimethyloxirane, 2,2-dimethyloxirane, 2-methyl-2-(4-methylcyclohex-3-en-1-yl)oxirane, 2-methyl-2-(4-methylcyclohex-3-en-1-yl)oxirane, 2-ethenyloxirane, 2-ethenyl-2-methyloxirane, 2-methyl-3-propyloxirane, and 2,3-diethyloxirane.
The method of the invention may be used for a variety of purposes, like bulk chemical synthesis (biocatalysis). Alkenes are efficiently epoxidized by peroxygenases. Propylene oxide is a highly reactive substance and one of the most important chemical intermediates. It is the starting material for a broad spectrum of products, including polymers (polyurethanes, polyesters), oxygenated solvents (propylene glycol ethers) and industrial fluids (monopropylene glycol and polyglycols). Annually 6,500,000 MT are produced. Other longer chain alkenes including branched alkenes are epoxidized in a similar manner—including butene and isobutene.
Polymerization of an epoxide gives a polyether, for example ethylene oxide polymerizes to give polyethylene glycol, also known as polyethylene oxide.
The methods of the invention may be carried out with an immobilized peroxygenase.
The methods of the invention may be carried out in an aqueous solvent (reaction medium), various alcohols, ethers, other polar or non-polar solvents, or mixtures thereof. By studying the characteristics of the aliphatic hydrocarbon used in the methods of the invention, suitable examples of solvents are easily recognized by one skilled in the art. By raising or lowering the pressure at which the oxidation is carried out, the solvent (reaction medium) and the aliphatic hydrocarbon can be maintained in a liquid phase at the reaction temperature.
The methods according to the invention may be carried out at a temperature between 0 and 90° C., preferably between 5 and 80° C., more preferably between 10 and 70° C., even more preferably between 15 and 60° C., most preferably between 20 and 50° C., and in particular between 20 and 40° C.
The methods of the invention may employ a treatment time of from 10 seconds to (at least) 24 hours, preferably from 1 minute to (at least) 12 hours, more preferably from 5 minutes to (at least) 6 hours, most preferably from 5 minutes to (at least) 3 hours, and in particular, from 5 minutes to (at least) 1 hour.
The present invention is further described by the following examples that should not be construed as limiting the scope of the invention.
EXAMPLES
The amino acid sequence of the peroxygenase from Agrocybe aegerita is shown as SEQ ID NO: 1.
Example 1
Alkene Epoxidation Catalyzed by a Fungal Peroxygenase
Reagents
Commercially available chemicals were purchased from Sigma-Aldrich, TCI Europe and Chemos GmbH, except for 2,3-epoxy-2-methylbutane which was purchased from Acros Organics. The extracellular peroxygenase of Agrocybe aegerita (wild type, isoform II, 44 kDa) was produced and purified as described previously. The enzyme preparation was homogeneous by SDS polyacrylamide gel electrophoresis and exhibited an A418/A280 ratio of 1.86. The specific activity of the peroxygenase was 63 U mg−1, where 1 U represents the oxidation of 1 μmol of 3,4-dimethoxybenzyl alcohol to 3,4-dimethoxybenzaldehyde in 1 min at 23° C.
Reaction Conditions
Typical reaction mixtures (total volume: 0.2 ml; 1.2 ml for gaseous alkenes) contained purified peroxygenase (1-2 U ml−1, 0.38-0.76 μM) dissolved in potassium phosphate buffer (10 mM, pH 7.0), acetone (60%, pH 5.3), and the alkene substrate (5% vol/vol; except for +/− limonene 5 mM of the substrate was used). The reactions were started by the addition of H2O2 via a syringe pump (4 mM h−1, except for 2-methyl-2-butene and 2,3-dimethyl-2-butene 2 mM h−1 was used), stirred at room temperature for 30 min, and stopped at which time chromatographic analyses showed that product formation was complete. Gaseous propene and n-butene were treated under the same conditions but by continuously bubbling the pure gas through the reaction vial (approx. 1 l h−1). The reaction mixtures were extracted with hexane (0.1 ml) by vigorous shaking.
Product Identification
The reaction products were analyzed by GC using a Hewlett Packard 6890 chromatograph equipped with a Hewlett Packard 5973 mass spectrometer and a ZB-Wax plus capillary column (250 μm diameter by 30 m length, 0.25 μm film thickness, Phenomenex, Torrance, Calif., USA). For analysis, 1 μl of the hexane extract was injected into the GC-system. GC was performed using various temperature profiles in dependence of the analyte. Propene: 30° C. hold 2 min; 1-butene: 35° C. hold 3.5 min, 30° C. min−1 to 100° C.; 1-pentene: 50° C. hold 3.5 min, 40° C. min−1 to 115° C.; 1-hexene, 2-hexene and 3-hexene: 70° C. hold 3.5 min, 40° C. min−1 to 135° C.; 1-heptene: 90° C. hold 3.5 min, 40° C. min−1 145° C.; 1-octene: 110° C. hold 3.5 min, 20° C. min−1 to 120° C.; +/−limonene: 70° C., 5° C. min−1 to 125° C., 30° C. min−1 to 230° C.; cis/trans-2-butene, isobutene and 1,3-butadiene: 35° C. hold 10 min; cyclopentene and cycloheptene: 45° C. hold 3 min, 20° C. min−1 to 250° C.; isoprene: 45° C. hold 5 min, 10° C. min−1 to 100° C. Helium was the carrier gas, in all cases, at a column flow rate of 1.5 ml min−1. The products were identified relative to authentic standards by their retention times and/or by electron impact MS at 70 eV.
Chiral Separation
The chiral separation of epoxides was performed by GC/MS using the above apparatus but fitted with a Beta DEXTM 120 capillary column (250 μm in diameter by 30 m length, 0.25 μm film thickness, Supelco, Bellefonte, Pa., USA). GC was performed using various temperature profiles. 1-hexene: 45° C. hold 20 min; 1-heptene: 45° C. hold 37 min; 1-octene: 55° C. hold 46 min; 1-octyne: 45° C. hold 2 min, 10° C./min to 155° C. The products were identified relative to authentic standards by their retention time and by electron impact MS at 70 eV.
Product Quantification
Quantitative analyses of the reaction products were performed by GC/MS as described above, using external standard curves of the respective authentic standards. All standard curves had linear regression values of R2>0.98.
Results














TABLE 1 A











Total





Alcohol
Amount
Epoxide
Amount
Product
Epoxide


No.
Substrate
Product
(μM)
Product
(μM)
(μM)
(%)







 1




—
—




 117
 117
100


 


 2








20




 60
 80
 75


 


 3








28




 12
 40
 31


 


 4








6




  6
 12
 50


 


 5








1




  9
 10
 88


 


 6








88




 106
 194
 55


 


 7




—
—




 989
 989
100


 


 8




—
—




 496
 496
100


 


 9




—
—




 900
 900
100


 


10




—
—




1910
1910
100


 


11




—
—




 912
 912
100


 


12








247




460/309
1020
 76 (46/30)


 


13








163




561/360
1084
 85 (52/33)


 


14




—
—




nd
nd
nd


 


15




—
—




nd
nd
nd


 


16




nd
nd




nd
nd
nd


 


17




nd
nd




nd
nd
nd


 


18




nd
nd




nd
nd
nd


 


19




nd
nd




nd
nd
nd





“nd” means that the reaction was carried out and the product was identified, but the product yield was not determined.














TABLE 1B





Substrate
IUPAC name of the respective epoxide products


No.
(the formulae are given in column 5 of table 1A)
















1
2-methyloxirane


2
2-ethyloxirane


3
2-propyloxirane


4
2-butyloxirane


5
2-pentyloxirane


6
2-hexyloxirane


7
2,2,3-trimethyloxirane


8
2,2,3,3-tetramethyloxirane


9
(2S,3S)-2,3-dimethyloxirane


10
(2R,3S)-2,3-Dimethyloxirane


11
2,2-dimethyloxirane


12
(4R,6R)-1-methyl-4-(prop-1-en-2-yl)-7-



oxabicyclo[4.1.0]heptane/2-methyl-2-(4-methylcyclohex-



3-en-1-yl)oxirane


13
(4S,6R)-1-methyl-4-(prop-1-en-2-yl)-7-



oxabicyclo[4.1.0]heptane/2-methyl-2-(4-methylcyclohex-3-



en-1-yl)oxirane


14
2-ethenyloxirane


15
2-ethenyl-2-methyloxirane/2-(prop-1-en-2-yl)oxirane


16
2-methyl-3-propyloxirane


17
2,3-diethyloxirane


18
6-oxabicyclo[3.1.0]hexane


19
8-oxabicyclo[5.1.0]octane









Example 2
Epoxidation of 1-Octene Using Different Fungal Peroxygenases
The peroxygenases shown in Table 2 were used in Example 2.









TABLE 2





Name
Source organism
Amino acid sequence







Peroxygenase 1
Coprinopsis cinerea
SEQ ID NO: 2


Peroxygenase 2
Chaetomium virescens
SEQ ID NO: 7


Peroxygenase 3
Humicola insolens
SEQ ID NO: 8


Peroxygenase 4
Chaetomium globosum
SEQ ID NO: 9


Peroxygenase 5
Daldinia caldariorum
SEQ ID NO: 14


Peroxygenase 6
Myceliophthora fergusii
SEQ ID NO: 15


Peroxygenase 7
Myceliophthora hinnulea
SEQ ID NO: 16


Peroxygenase 8
Thielavia hyrcaniae
SEQ ID NO: 18


Peroxygenase 9
Pestalotiopsis virgatula
SEQ ID NO: 19









Reactions were carried out in capped 2 mL HPLC glass vials at the following conditions: 10 mM phosphate buffer pH 6.5, 20% v/v acetonitrile, 1 mM 1-octene, 0.01 mg/mL peroxygenase (see Table 3), 1 mM hydrogen peroxide, in a total reaction volume of 800 μL. Reaction mixtures were stirred by magnet at room temperature ( ̃25° C.) for 30 minutes, and the reaction was stopped by adding 5 μL catalase (Terminox Ultra 50L, Novozymes).
Samples were extracted by mixing with 760 μL ethyl acetate containing 0.01% w/v BHT (2,6-di-tert-butyl-4-methylphenol). The ethyl acetate extracts were analyzed by GC-MS on a gas chromatograph (model 7890A) equipped with an autosampler (model 7693A) and a mass selective detector (model 5975C) from Agilent (Santa Clara Calif., USA) as follows: samples were injected in split mode (10:1) on a Zebron DB-5HT Inferno column (15 m, 250 μm, 0.25 μm) from Phenomenex (Torrance Calif., USA) and eluted with 1.1 mL/min Helium using the following temperature program: 45° C. (for 1 min), 45-75° C. at 10° C./min, 75-275° C. at 40° C./min and 275° C. (1 minute). The mass detector was operated in scan mode and the Total Ion Count (TIC) chromatogram was used to determine the areas of the substrate and product peaks. Peaks were identified by comparing the mass spectra with spectra from the mass spectral library available in the GC software (NIST MS search version 2.0). Substrate and product concentrations were determined by external calibration with authentic compounds using BHT (2,6-di-tert-butyl-4-methylphenol) as internal standard.
The enzymatic conversion of 1-octene (substrate) to 1,2-epoxyoctane (product) is shown in Table 3. Due to the volatility of 1-octene, a large part of the substrate was lost by evaporation during the reaction.







TABLE 3







Concentration of remaining substrate and reaction product when reaction


was stopped.












Concentration of
Concentration of




1-octene
1,2-epoxyoctane



Enzyme
(mM)
(mM)







Peroxygenase 1
0.07
0.02



Peroxygenase 2
0.09
0.02



Peroxygenase 3
0.07
0.19



Peroxygenase 4
0.10
0.01



Peroxygenase 5
0.10
0.01



Peroxygenase 6
0.07
0.02



Peroxygenase 7
0.12
0.02



Peroxygenase 8
0.09
0.04



Peroxygenase 9
0.12
0.01










Example 3
Epoxidation of Different Alkenes Using a Humicola Peroxygenase
Reactions were carried out in capped 2 mL HPLC glass vials at the following conditions: 10 mM phosphate buffer pH 6.5, 20% v/v acetonitrile, 1 mM substrate (see Table 4), 0.01 mg/mL of peroxygenase 3 (see Example 2), 1 mM hydrogen peroxide, in a total reaction volume of 800 μL. Reaction mixtures were stirred by magnet at room temperature ( ̃25° C.) for 30 minutes, and the reaction was stopped by adding 5 μL catalase (Terminox Ultra 50L, Novozymes).
Samples were extracted by mixing with 760 μL ethyl acetate containing 0.01% w/v BHT (2,6-di-tert-butyl-4-methylphenol) as internal standard. The ethyl acetate extracts were analyzed by GC-MS as described in Example 2. Due to lack of authentic standards and high volatility of some substrates, product yields were calculated as the Area/Aistd of product in the sample compared to the Area/Aistd of a standard sample with 1 mM substrate dissolved in ethyl acetate containing 0.01% w/v BHT, assuming the same response factor for substrate and products. Results are shown in Table 4.







TABLE 4







Results for epoxidation of different alkenes using Peroxygenase 3.











Substrate
Main product
Product yield







1-Octene
1.2-epoxyoctane
15%



trans-2-Octene
2,3-epoxyoctane
63%



trans-3-Octene
3,4-epoxyoctane
69%



trans-4-Octene
4,5-epoxyoctane
76%



1,9-Decadiene
1,2-epoxy-9-decene
13%










Example 4
Epoxidation of Trans-2-Octene Using a Humicola Peroxygenase
Reactions were carried out in capped 2 mL HPLC glass vials under the following conditions: 10 mM phosphate buffer pH 6.5, 20% v/v acetonitrile, 20 g/L trans-2-octene, 0.1 or 0.5 mg/mL of peroxygenase 3 (see Example 2), 160 μL of 1 M hydrogen peroxide dosed during the reaction (2 hours) with a multi-channel syringe pump (model 220-CE, World precision instruments, Aston, Stevenage, UK) using 1 mL gas tight glass syringes (SGE Analytical Science, Ringwood, Australia); in a final reaction volume of 800 μL. Reaction mixtures were stirred by magnet at room temperature ( ̃25° C.) for 2 hours, and the reaction was stopped by adding 5 μL catalase (Terminox Ultra 50L, Novozymes).
Samples were extracted by mixing with 780 μL ethyl acetate containing 0.1% w/v BHT (2,6-di-tert-butyl-4-methylphenol) as internal standard. The ethyl acetate extracts were diluted 100 times with ethyl acetate without internal standard and analyzed by GC-MS as reported in Example 2. Formation of epoxide was measured as the area percentage of epoxide compared to the area sum of substrate and products, assuming the same response factor for substrate and product.







TABLE 5







Results from epoxidation of trans-3-octene using Peroxygenase 3.










Peroxygenase concentration
Yield of 2,3-epoxyoctane














  0 mg/mL
0%



0.1 mg/mL
3%



0.5 mg/mL
40%

## Claims

1. A method for producing an epoxide, comprising contacting a non-cyclic aliphatic alkene or a terpene with hydrogen peroxide and a peroxygenase (EC 1.11.2.1), wherein the peroxygenase comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1.

2. The method of claim 1, wherein the peroxygenase comprises an amino acid sequence having at least 95% sequence identity to SEQ ID NO: 1.

3. The method of claim 1, wherein the peroxygenase comprises an amino acid sequence having at least 97% sequence identity to SEQ ID NO: 1.

4. The method of claim 1, wherein the peroxygenase comprises an amino acid sequence having at least 98% sequence identity to SEQ ID NO: 1.

5. The method of claim 1, wherein the peroxygenase comprises an amino acid sequence having at least 99% sequence identity to SEQ ID NO: 1.

6. The method of claim 1, wherein the peroxygenase comprises the amino acid sequence of SEQ ID NO: 1.

7. The method of claim 1, wherein the amino acid sequence comprises the motif E-H-D-[G,A]-S-[L,I]-S-R (SEQ ID NO: 21).

8. The method of claim 1, wherein the aliphatic alkene has one or more substituents selected from the group consisting of halogen, hydroxyl, carboxyl, amino, nitro, cyano, thiol, sulphonyl, formyl, acetyl, methoxy, ethoxy, carbamoyl and sulfamoyl.

9. The method of claim 8, wherein the substituent(s) are selected from the group consisting of chloro, hydroxyl, carboxyl and sulphonyl.

10. The method of claim 1, wherein the aliphatic alkene consists of at least three carbons, and has a carbon-carbon double bond at one end.

11. The method of claim 1, wherein the aliphatic alkene is propene, butene, pentene, hexene, heptene, octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene, or hexadecene, or an isomer thereof.

12. The method of claim 1, wherein the aliphatic alkene is propene, 1-butene, 1-pentene, 1-hexene, 2-hexene, 3-hexene, 1-heptene, 1-octene, 2-methyl-2-butene, 2,3-dimethyl-2-butene, cis/trans-2-butene, isobutene, 1,3-butadiene, and isoprene; or an isomer thereof.

13. The method of claim 1, wherein the aliphatic alkene is unsubstituted.

14. The method of claim 1, wherein the aliphatic alkene is linear.

15. The method of claim 1, wherein the terpene is isoprene or a monoterpene.

16. The method of claim 1, wherein the terpene is a cyclic terpene.

17. The method of claim 16, wherein the cyclic terpene is a monocyclic monoterpene.

18. The method of claim 17, wherein the monocyclic monoterpene is limonene.