Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
  • C07D233/54—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members
  • C07D233/66—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D233/84—Sulfur atoms
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/41—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having five-membered rings with two or more ring hetero atoms, at least one of which being nitrogen, e.g. tetrazole
  • A61K31/4164—1,3-Diazoles

Definitions

• ESH ergothioneine
• ESH ovothiol A
• ovothiol A also serves as an anti-oxidant albeit in sea urchin eggs as well as in the pathogens, Leishmania major and Trypanosoma cruzi. 5
• the sulfoxide is the substrate for the mycobacterial enzyme, EgtE.
• EgtE mycobacterial enzyme
• the absolute chirality of the sulfoxide is not known for the natural substrate or the synthetic one.
• Prior synthesis of intermediate (II) was reported in 1974 but was elaborate and irreproducible, and resulted in a low overall yield of 8.5%. 15 The authors reported only the position of the aromatic proton resonance and no further structural confirmation.
• the m.p. of both natural and synthetic product was recorded as 188-190 °C.
• ESH is synthesized by the sequential action of five enzymes, encoded by the genes egtA, egtB, egtC, egtD and egtE (Scheme 1 ).
• EgtA is considered to be a ⁇ -glutamyl cysteine ligase and catalyzes the formation of y- glutamylcysteine.
• Histidine is methylated by an S-adenosylmethionine (SAM) dependant methyl transferase, EgtD, to give the trimethyl ammonium betaine, hercynine.
• SAM S-adenosylmethionine
• Hercynine is then converted into S-(P-amino ⁇ -carboxyethyl)ergothioneine sulfoxide (II), via an iron (II)-dependent oxidase (EgtB) which requires oxygen and ⁇ -glutamylcysteine to produce ⁇ - glutamylcysteinylhercynine (I).
• II iron-dependent oxidase
• EgtC a putative class-ll glutamine amidotransamidase
• PDP pyridoxal 5- phosphate
• OvoA is an iron (II) dependent sulfoxide synthase which catalyzes the first step in ovothiol A synthesis and is a homolog of EgtB.
• the substrate specificity of EgtB vs. OvoA in achieving C-S bond formation differs significantly.
• OvoA is very selective for its sulfur donor substrate and only accept L-cysteine while it prefers histidine as co-substrate.
• EgtB require ⁇ -glutamyl-L-cysteine as sulfur donor.
• OvoA switches its sulfurization pattern on the histidine ring from the ⁇ -carbon to the ⁇ -carbon depending on the level of a-A/-methylation.
• OvoA converts hercynine directly into S- (P-amino-p-carboxyethyl)ergothioneine sulfoxide (II) and produces a minor amount of the ⁇ - sulfoxide (ovothiol substitution pattern) when ⁇ - ⁇ /,/V-dimethyl histidine is used as the co- substrate (Scheme 1 ).
• R may be when n is 1
• R may be when n is
• R may be when n is 0;
• R may be H.
• the compound of formula V may be selected from the group consisting of:
• the compound of formula 1 1 may be a protected L-histidine.
• step (d) dimethylformamide (DMF) and /V-bromosuccinimide (NBS) may be used to form the 5-bromohercynine lactone. At least 2 mol equivalents, and preferably at least 2,5 mol equivalents, of NBS relative to compound 14 may be used. Prior to performing step (e), the 5-bromohercynine lactone may be isolated from other products formed in step (d), such as 2, 5-bromohercynine.
• DMF dimethylformamide
• NBS V-bromosuccinimide
• step (e) cysteine or thioacetic acid may be used to form the compound of formula 15.
• Steps (d) and (e) may be performed together in one-pot synthesis.
• step (h) pyridoxal-5 phosphate (PLP) may be used to form the ergothioneine of formula IV.
• the sulfoxide of formula II may be further converted to ergothioneine of formula IV.
• the sulfoxide of formula II may be contacted with an enzyme encoded by the egrfE gene, and preferably the EgtE enzyme, to form the ergothioneine of formula IV.
• the sulfide of formula 15 formed in step (e), or any one of the intermediate compounds formed in the process, such as 5-bromohercynine, may be labelled with a stable isotope, for example deuterium.
• the labelled compound or intermediate may be for use in the study of the biosynthesis pathway of ergothioneine or as an internal standard in the quantitation of pathway metabolites during external stimuli or drug treatment.
• ESH ergothioneine
• the compound of formula 15 may be contacted with a crude enzyme extract of M. smegmatis or EgtE.
• ergothioneine of formula IV or a physiologically acceptable salt thereof, a tautomer, a stereoisomer or a mixture of stereoisomers
• FIG. 2 Non enzymatic production of ESH catalysed by PLP.
• TIC extracted for ESH and PLP using S-(p-amino-p-carboxyethyl)ergothioneine sulfide (15), S-( -amino-p- carboxyethyl)ergothioneine sulfoxide (II) and S-( -amino- -carboxyethyl)ergothioneine sulfone (III).
• FIG. 15A TIC of S-(P-amino-p-carboxyethyl)ergothioneine sulfoxide (II).
• Figure 16A TIC of S-(p-amino-p-carboxyethyl)ergothioneine sulfone (III).
• Figure 18 Overlaid TIC of Ergothioneine. Retention time of 1 .5 min.
• Figure 19 ESI/QTOF mass spectra of ESH standard in positive ion mode.
• the invention provides a process for synthesising a compound of formula V
• n 0, 1 or 2;
• R is H or (where the wavy line indicates the point of attachment of R to the rest of the molecule of formula V); or a physiologically acceptable salt, tautomer, stereoisomer or mixture of stereoisomers thereof.
• the process utilizes a /V-benzyl protected histidine rather than the unprotected form of histidine which is used by known processes of forming compounds of formula V, such as ergothioneine, ( -amino-p-carboxyethyl)ergothioneine sulfide, ( ⁇ -amino-p- carboxyethyl)ergothioneine sulfoxide and (P-amino-3-carboxyethyl)ergothioneine sulfone.
• the process of the invention comprises the steps of:
• 5-bromohercynine 2 5-bromohercynine e) converting the 5-bromohercynine lactone of step (d) to ( -amino-p carboxyethyl)ergothioneine sulfide of formula 15
• a suitable /V-benzyl protected histidine is commercially available from Sigma-Aldrich under the trade name A/a-Boc-/V(im)-benzyl-L-histidine.
• the process may include a step of forming a suitably blocked histidine.
• Bacteria, and in particular mycobacteria can be used to enzymatically produce the ergothioneine from the synthetically produced S- ⁇ -amino- - carboxyethyl)ergothioneine sulfide or S-( -amino-p-carboxyethyl)ergothioneine sulfoxide (II).
• Suitable bacteria produce the EgtE enzyme and include Claviceps purpurea. Neurospora crassa and Mycobacterium smegmatis.
• the ergothioneine produced according to the process of the invention can be used as a neutraceutical, cosmeceutical, hair care product, product to assist with recovery after sport and so forth.
• the product can be formulated for topical application or oral administration.
• the sulfone of formula III may be used as an inhibitor of ergothioneine synthesis or in identifying or designing an inhibitor in the ergothioneine synthesis pathway.
• Two different routes to the target compound, S-(p-amino-p-carboxyethyl)ergothioneine sulfoxide (II) were attempted by the applicant before the process of the present invention was conceived.
• reaction may possibly occur via the formation of the cyclic ethylenimine carboxylic acid intermediate produced by an intramolecular S N 2 reaction of the ⁇ -chloroalanine (2), followed by the ring opening induced by nucleophilic attack of the sulfur atom of ESH, giving the major product A/-Boc methyl ester (3a).
• the process of the invention is capable of providing an overall yield which is at least 2 times better than any prior published process.
• the final step can be achieved in either chemical, biosynthetic or microbial means.
• the chemical transformation involves a pyrolytic C-S cleavage.
• biomimetic pyridoxal phosphate (PLP) mediated cleavage of the sulfide or sulfoxide substrates as well as with crude enzymatic extracts of M. smegmatis gave ESH. (Schemes 3 and 4).
• the control reaction containing only the crude M. smegmatis cell free extract was also treated under the same conditions as the metabolites.
• the concentration of ESH thus obtained was 5.70 ( ⁇ 0.30) ng /ml, which was equated to that of endogenous ESH. This concentration was above the limit of detection (0.78 ng/ml), thus any increase in the concentration of ESH in the experiment above 1 ng/ml is considered significant enough to be ascribed to basal levels or biotransformation of the respective substrates by the crude endogenous enzymes of the ESH pathway.
• (P-amino-p-carboxyethyl)ergothioneine sulfoxide (II) biosynthetically produced the highest concentration of ESH (22.6 ng/ml) (Fig. 1 ).
• the increased yield which is obtained by the process of the invention will also allow intermediates to be recovered in higher quantities for isotopic labelling.
• the high yields of the intermediate products also allow viable isotopic labelling steps to be performed. Isotopes are usually very expensive and are advantaged by high yield conversions.
• Optical rotations were obtained using a Perking Elmer 141 polarimeter at 20 °C.
• the concentration c refers to g/100ml.
• Mass spectra were recorded on a JEOL GC MATE II magnetic sector mass spectrometer and the base peaks are given, University of Cape Town.
• cysteine HCI. H 2 0 (1 .07 g, 6.08 mmol) was added in one portion and the resulting solution was allowed to stir at room temperature for 24 hours.
• Reverse phase chromatography C18 afforded the product 15 isolated as the yellow hygroscopic solid acetate salt form (695 mg, 90%).
• M. smeg culture 800 ml was grown to exponential phase, and then dried to obtain 10 g of dry cells. The obtained pellets of M. smeg cells were thereafter stored at -80 °C until it was required.
• M.smeg cells were sonicated for 35minutes at 4°C (25 pulsars), followed by the addition of potassium phosphate buffer (60 ml; pH 7). The solution was allowed to stir at 4°C for 10 minutes and thereafter centrifuged at 3000 rpm for 20 min. The supernatant was collected, measured and then the appropriate amount of ammonium sulphate gradually added while stirring at 4 °C overnight to obtain 60-70 % saturation. 28
• the complex total protein ammonium salts precipitate was resuspended in buffer mixture (20 ml; pH 7) containing py idoxal phosphate (10 ml; 20 ⁇ ), potassium phosphate buffer (8 ml; 50 mM; pH 7) and (2 ml; 1 mM EDTA).
• the calculated M. smeg total protein concentration was found to be 10.33 ⁇ / ⁇ .
• Hercynine-d 3 (7) was synthesized in a two-step reaction starting with commercially available L-histidine (Scheme 2).
• the first step involved reductive amination using aqueous formaldehyde and sodium triacetoxyborohydride to give N,N-d ⁇ methyl histidine (6).
• the second step involved the quaternarization of the crude A/,/V-dimethyl histidine (6) using methyl-d 3 iodide under basic conditions to give the hercynine-c/ 3 (7).
• ESH-d 3 (10) was synthesized in two sequential reaction steps starting with the S-terf-butyl protected 2-mercapto-histidine (9), derived from mercapto histidine (8). 21 Selective N- methylation with methyl-d 3 iodide, followed by S-terf-butyl deprotection using 2- mercaptopropionic acid (terf-butyl scavenger) in HCI gave ESH-d 3 (10).

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