Frank Wuggenig

Direct liquid chromatographic enantioseparation of chiral α- and β-aminophosphonic acids employing quinine-derived chiral anion exchangers: determination of enantiomeric excess and verification of absolute configuration

Four types of quinine-derived chiral anion exchangers were used for the direct liquid chromatographic separation of enantiomers of chiral but N-protected α- and β-aminophosphonic acids. The respective and easily prepared 3,5-dinitrobenzyloxycarbonyl and dinitrophenyl derivatives were well separated, yielding α-values between 1.1 and 2.8 and resolution values in the range 2.0–9.0. Besides the chromatographic investigations, data on enantiomeric excesses (ees) and the absolute configurations of some enantiomerically enriched α- and β-aminophosphonic acids prepared by stereoselective synthesis were also determined. The results obtained by this method (ee and absolute configuration) correspond well with the results previously obtained by a 31P-NMR spectroscopic method.

Enzymes in organic chemistry. Part 9:Chemo-enzymatic synthesis of phosphonic acid analogues of l-valine, l-leucine, l-isoleucine, l-methionine and l-α-aminobutyric acid of high enantiomeric excess

Abstract Diisopropyl α-chloroacetoxyphosphonates derived from propanal, isobutanal, 3-methylmercaptopropanal, 3-methylbutanal and ( S )-2-methylbutanal were resolved by enzyme-catalysed hydrolysis. Lipases preferentially hydrolysed the ( S )-esters and protease Chirazyme ® P-2 the ( R )-esters. Replacing the isopropyl groups by t -butyl groups reduced the reaction rate; replacing them by a 2,2-dimethylpropane-1,3-diyl group increased the reaction rate. ( S )-α-Hydroxyphosphonates (ee 92–99%), obtained with the protease except one, were transformed into phosphonic acid analogues of l -valine, l -leucine, l -isoleucine, l -methionine and l -α-aminobutyric acid. Their enantiomeric purity was determined by HPLC on a chiral stationary phase after derivatisation at nitrogen.

Enzymes in organic chemistry. Part 10: Chemo-enzymatic synthesis of l-phosphaserine and l-phosphaisoserine and enantioseparation of amino-hydroxyethylphosphonic acids by non-aqueous capillary electrophoresis with quinine carbamate as chiral ion pair agent

Abstract Diisopropyl 2-azido-1-acetoxyethylphosphonate (±)- 7 was hydrolysed with high enantioselectivity by lipase SP 524 to give α-hydroxyphosphonate ( S )-(−)- 6 and ester ( R )-(−)- 7 , which was saponified to give ( R )-(+)- 6 . The two α-hydroxyphosphonates ( R )- and ( S )- 6 were transformed into l-phosphaisoserine and l -phosphaserine, respectively. Their enantiomeric excesses were determined to be 97% by HPLC on an chiral stationary phase. A mixture of all four stereoisomeric amino-hydroxyethylphosphonic acids can be separated by non-aqueous capillary electrophoresis with quinine carbamate as the chiral ion pair agent applying the partial filling technique.

Low‐molecular‐weight chiral cation exchangers: Novel chiral stationary phases and their application for enantioseparation of chiral bases by nonaqueous capillary electrochromatography

Cation exchange type chiral stationary phases (CSPs) based on 3,5‐dichlorobenzoyl amino acid and amino phosphonic acid derivatives as chiral selectors (SOs) and silica as chromatographic support were developed and applied to enantiomer separations of chiral bases by nonaqueous capillary electrochromatography (NA‐CEC). As a rationale for efficient CSP development we adopted the combined use of the “reciprocity principle of chiral recognition” and nonaqueous ion‐pair CE as screening assay. Thus, (S)‐atenolol was employed as chiral counter‐ion added to the BGE in CE and a series of N‐derivatized amino acids and amino phosphonic acids were screened to derive reciprocally information on their chiral recognition abilities for atenolol enantiomers. Two SO candidates, namely N‐(3,5‐dichlorobenzoyl)‐O‐allyl‐tyrosine and N‐(4‐allyloxy‐3,5‐dichlorobenzoyl)‐1‐amino‐3‐methylbutane phosphonic acid that have been identified as potential SOs in the CE screening were, after immobilization on thiol‐modified silica, evaluated in cation‐exchange NA‐CEC. The strong chiral cation exchanger with the free phosphonic acid group exhibited enhanced enantioselectivity compared to the weak chiral cation exchanger with the carboxylic acid group. A wide variety of chiral bases could be successfully resolved on the strong chiral cation exchanger with α‐values up to 2.2 and efficiencies up to 375 000 m–1 including β‐blockers and other amino alcohols, local anesthetics like etidocaine, antimalarial agents like mefloquine, Tröger’s base, phenothiazines like promethazine, and antihistaminics. The influence of several experimental parameters (electrolyte concentration, acid‐base ratio and acetonitrile‐methanol ratio) was evaluated *.

Enzymes in Organic Chemistry VI [1]. Enantioselective Hydrolysis of 1-Chloroacetoxycycloalkylmethylphosphonates with Lipase AP 6 from Aspergillus niger and Chemoenzymatic Synthesis of Chiral, Nonracemic 1-Aminocyclohexyl- methylphosphonic Acids

Summary. Racemic α-chloroacetoxyphosphonates derived from cycloalkanecarbaldehydes and three branched aldehydes were prepared and tested for kinetic resolution by lipase AP 6 which hydrolyses preferentially the (S) esters. The enantiomeric excess and the reaction rate are significantly influenced by the size of the cycloalkyl group. The optical antipodes of α- hydroxycyclohexylmethylphosphonates (3d; ee 90% and ≥99%, respectively) were transformed into the corresponding α-aminophosphonic acids 6.Zusammenfassung. Racemische α-Chloroacetoxyphosphonate, die sich von Cycloalkancarbaldehyden und drei verzweigten Aldehyden ableiten, wurden hergestellt und für die kinetische Racematspaltung mit der Lipase AP 6, die bevorzugt die (S)-Ester hydrolysiert, verwendet. Der Enantiomerenüberschuß und die Reaktionsgeschwindigkeit werden signifikant von der Ringgröe des Cycloalkylrestes beeinflußt. Die optischen Antipoden des α-Hydroxycyclohexylmethylphosphonates (3d; ee 90% bzw. ≥ 99%) wurden in die entsprechenden α-Aminophosphonsäuren 6übergeführt.

Synthesis of chiral, nonracemic α-sulfanylphosphonates and derivatives

Abstract Optically active α-sulfanylphosphonates and the corresponding methyl sulfides were prepared in three steps starting from chiral, nonracemic (ee 93–97%) α-hydroxyphosphonates obtained by enzymatic resolution. Reaction conditions for the reduction of racemisation-prone substrates were found to preserve the enantiomeric excesses.

ENZYMES IN ORGANIC CHEMISTRY 7.[1] EVALUATION OF HOMOCHIRAL t-BUTYL(PHENYL)PHOSPHINOTHIOIC ACID FOR THE DETERMINATION OF ENANTIOMERIC EXCESSES AND ABSOLUTE CONFIGURATIONS OF α-SUBSTITUTED PHOSPHONATES

Abstract α-Hydroxy-, α-acetoxy-. α-chloroacetoxg, α-azido-, α-phthalimidooxy-, and α-aminooxy-phosphonates are investigated by 1H and 31P NMR spectroscopy in the presence of homochiral t−butyl(phenyl)phosphinothioic acid as chiral solvating agent. The 31P NMR shift differences for the diastereomeric complexes of α-hydroxyphosphonates are large (0.10 -0.30 ppm) and allow the determination of their enantiomeric excess and the cautious assignment of their absolute configuration.

On the Transformation of (S)‐2‐Hydroxypropylphosphonic Acid into Fosfomycin in Streptomyces fradiae—A Unique Method of Epoxide Ring Formation

(1S,2S)‐ and (1R,2S)‐2‐hydroxy‐[1‐D1]propylphosphonic acid were synthesised from (1S,2S)‐2‐benzyloxy‐[1‐D1]propanol, which was obtained by horse liver alcohol dehydrogenase catalysed reduction of the corresponding aldehyde. When (1S,2S)‐2‐hydroxy‐[1‐D1]propylphosphonic acid was fed to Streptomyces fradiae, the deuterium was retained to the same extent in fosfomycin (cis‐epoxide) and its co‐metabolite trans‐epoxide. Removal of the hydrogen (deuterium) atom from the C‐1 atom of deuterated 2‐hydroxypropylphosphonic acids is a stereospecific process (the hydrogen atom of (S)‐2‐hydroxypropylphosphonic acid is pro‐R). The formation of the OC‐1 bond of fosfomycin occurs with net inversion of configuration, the formation of the OC‐1 bond of the trans‐epoxide with net retention.

Indirect Evidence for the Biosynthesis of (1S,2S)‐1,2‐Epoxypropylphosphonic Acid as a Co‐Metabolite of Fosfomycin [(1R,2S)‐1,2‐Epoxypropylphosphonic Acid] by Streptomyces fradiae

Treatment of the culture broth of fosfomycin (1) producing Streptomyces fradae with ammonia gives 2−3% of the C-1 epimeric compound 5, as well as the known (1R,2R)-2-amino-1-hydroxypropylphosphonic acid (3) derived from fosfomycin. The configuration of 5 was determined by capillary electrophoresis employing a quinine carbamate-type chiral selector and by synthesis from a monoprotected 1,2-dihydroxypropylphosphonate of known absolute configuration. It is postulated that (1S,2R)-2-amino-1-hydroxypropylphosphonic acid (5) is derived by ring opening of a trans-epoxide, formed as a co-metabolite of fosfomycin (cis-epoxide), with ammonia. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Studies on the biodegradation of fosfomycin: Synthesis of 13C-labeled intermediates, feeding experiments with rhizobium huakuii PMY1, and Isolation of Labeled Amino Acids from Cell Mass by HPLC

Racemic (1R*,2R*)-1,2-dihydroxy-[1-(13)C(1)]propylphosphonic acid and 1-hydroxy-[1-(13)C(1)]acetone were synthesized and fed to R. huakuii PMY1. Alanine and a mixture of valine and methionine were isolated as their N-acetyl derivatives from the cell hydrolysate by reversed-phase HPLC and analyzed by NMR spectroscopy. It was found that the carbon atoms of the respective carboxyl groups were highly (13)C-labeled (up to 65 %). Hydroxyacetone is therefore considered an obligatory intermediate of the biodegradation of fosfomycin by R. huakuii PMY1.