Biotransformation of alkyl and aryl carbonates. Microbial degradation

Summary An enriched mixed culture was successfully grown on model alkyl and aryl carbonates. These compounds were degraded by microorganisms at different rates.P-Chlorophenyl-2-octyl carbonate andp-nitrobenzyl-2-octyl carbonate were metabolized through the formation ofp-chlorophenol andp-nitrobenzyl alcohol respectively. A strain ofAcinetobacter calcoacefcus isolated from the mixed culture utilized phenyl-2-octyl carbonate by an intracellular hydrolase to phenol and 2-octanol which were further metabolized.     

First enantioselective hydrolysis of n-alkyl sec-alkyl carbonates by porcine pancreatic lipase

Summary n-Alkyl sec-alkyl carbonates were enantioselectively hydrolyzed by porcine pancreatic lipase to give optically active (R)-sec-alkanols. (R)-1-Phenylethanol with an optical purity of >99%ee was obtained by the resolving method.     

Alkaline phosphatase revisited: hydrolysis of alkyl phosphates

Escherichia coli alkaline phosphatase (AP) is the prototypical two metal ion catalyst with two divalent zinc ions bound approximately 4 A apart in the active site. Studies spanning half a century have elucidated many structural and mechanistic features of this enzyme, rendering it an attractive model for investigating the potent catalytic power of bimetallic centers. Unfortunately, fundamental mechanistic features have been obscured by limitations with the standard assays. These assays generate concentrations of inorganic phosphate (P(i)) in excess of its inhibition constant (K(i) approximately 1 muM). This tight binding by P(i) has affected the majority of published kinetic constants. Furthermore, binding limits k(cat)/K(m) for reaction of p-nitrophenyl phosphate, the most commonly employed substrate. We describe a sensitive (32)P-based assay for hydrolysis of alkyl phosphates that avoids the complication of product inhibition. We have revisited basic mechanistic features of AP with these alkyl phosphate substrates. The results suggest that the chemical step for phosphorylation of the enzyme limits k(cat)/K(m). The pH-rate profile and additional results suggest that the serine nucleophile is active in its anionic form and has a pK(a) of < or = 5.5 in the free enzyme. An inactivating pK(a) of 8.0 is observed for binding of both substrates and inhibitors, and we suggest that this corresponds to ionization of a zinc-coordinated water molecule. Counter to previous suggestions, inorganic phosphate dianion appears to bind to the highly charged AP active site at least as strongly as the trianion. The dependence of k(cat)/K(m) on the pK(a) of the leaving group follows a Br?nsted correlation with a slope of beta(lg) = -0.85 +/- 0.1, differing substantially from the previously reported value of -0.2 obtained from data with a less sensitive assay. This steep leaving group dependence is consistent with a largely dissociative transition state for AP-catalyzed hydrolysis of phosphate monoesters. The new (32)P-based assay employed herein will facilitate continued dissection of the AP reaction by providing a means to readily follow the chemical step for phosphorylation of the enzyme.     

Production of chiral epoxides: Epoxide hydrolase-catalyzed enantioselective hydrolysis

Chiral epoxides are highly valuable intermediates, used for the synthesis of pharmaceutical drugs and agrochemicals. They have broad scope of market demand because of their applications. A major challenge in modern organic chemistry is to generate such compounds in high yields, with high stereo- and regio-selectivities. Epoxide hydrolases (EH) are promising biocatalysts for the preparation of chiral epoxides and vicinal diols. They exhibit high enantioselectivity for their substrates, and can be effectively used in the resolution of racemic epoxides through enantioselective hydrolysis. The selective hydrolysis of a racemic epoxide can produce both the corresponding diols and the unreacted epoxides and vicinal diol has prompted researchers to explore their use in the synthesis of epoxides and diols with high ee values.     

Synthesis of substituted aryloxy alkyl and aryloxy aryl alkyl imidazoles as antileishmanial agents

A series of aryloxy alkyl/aryl alkyl imidazoles were synthesized and evaluated in vitro as antileishmanials against Leishmania donovani. All the 19 compounds exhibited 94–100% inhibition at 10 μg/mL against promastigotes and 12 compounds exhibited high inhibition with an IC₅₀ in the range of 0.47–4.85 μg/mL against amastigotes. Promising compounds were tested further in vivo. Among all, compounds 4 and 23 with 4-CF₃ aryloxy moiety exhibited medium in vivo inhibition of 58–60%, thus providing new structural lead for antileishmanials.     

Anomeric O-acylation of Kdo using alkyl and aryl isocyanates

To develop a convenient method for the preparation of an alpha-Kdo derivative carrying a functional spacer at the reducing end, we examined anomeric O-acylation using Kdo and halogenated alkyl/aryl isocyanates as nucleophile and electrophiles, respectively. Reaction of a Kdo derivative with 2-chloroethyl isocyanate in the presence of DMAP gave an alpha-spiro product (82%) and an alpha-Kdo derivative of a dimeric isocyanate adduct (10%). Similar reaction with 4-(chloromethyl)phenyl isocyanate gave only the corresponding alpha-spiro product (81%). The NMR data show that the pyranose rings of both the alkyl and aryl spiro products adopt the 5C2 conformation. Thus, we accomplished alpha-selective anomeric O-acylation by coupling the Kdo derivative with alkyl and aryl isocyanates.     

芳香酰胺类化合物的选择性水解菌初筛模型的研究

建立了一种快速筛选选择性水解手性芳香酰胺类化合物微生物的方法。在中性或弱碱性条件下,KMnO4能氧化芳香胺,但对芳香乙酰胺没有氧化效果。KMnO4被芳香胺还原而褪色,通过褪色程度来快速测定菌的酶活力及手性选择性。以1-苯基乙酰胺为例,得出最佳筛选体系:最大吸收波长为525 nm;1-苯基乙胺在0.04~5 mmol/L的浓度范围内与其ΔA525符合朗伯比尔定律;反应温度为60℃,反应时间为20 m in。通过该模型筛到5株选择性的菌株,R-选择性的菌株4株,S-选择性的菌株1株。     

Lipase-catalysed regio- and enantioselective deacetylation of 2,4-diacetoxyphenyl alkyl ketones.

Porcine pancreatic lipase in tetrahydrofuran catalyses the deacetylation of 2,4-diacetoxyphenyl alkyl ketones in a highly regioselective fashion. The strategy of regioselective deacetylation of diacetoxyphenyl alkyl ketones has also resulted in the enantiomeric resolution of a racemic diacetoxyphenyl alkyl ketone, i.e. (+/-)-2,4-diacetoxyphenyl (1-ethyl)pentyl ketone, a precursor for the synthesis of an antifungal coumarin, 7-acetoxy-4-(1-ethyl)pentyl-3-phenyl-2H-1-benzopyran-2-one.     

Mass and infrared spectra of diaryl and aryl alkyl sulfate diesters

The synthesis and the infrared and mass spectra of diaryl and aryl alkyl sulfate diesters are described. The mass spectra of these two classes of compounds consistently showed an intense molecular ion and two or three additional intense, diagnostic ions. Their infrared spectra also gave information useful for characterizing and differentiating these two classes of compounds.     

Alkyl sulfates and alkyl aryl sulfonates as inhibitors of penicillinase]

The kinetics of inhibition of penicillinase of Bac. licheniformis 749/c by various alkyl-sulphates (with a long hydrocarbon chain from C8 to C16), n-toluolsulphoacid and alkylbenzol-sulphonate (R-C12--C16) was studied. The inhibition rate increased with elongation of the alkyl radical and rising of the inhibitor concentraiton. This means that the determining factor in inhibition process was hydrophobic interaction of the alkyl chains and not the electrostatic interaction with the enzyme. In-vitro experiments with penicillinase-producing strains of staphylococcus showed that non-bactericidal concentrations of the alkylsulphates and alkylben zolsulphonates increased the effect of benzylpenicillin, ampicillin and methicillin. The highest increase in the antibiotic activity, as well as in the enzyme inhibition was observed with respect to the compound with the hydrocarbon chain fron C12 to C16. The increase in the activity of methicillin against the staphylococcal strains resistant simultaneously to benzylpenicillin, ampicillin and methicillin was indicative of possible using of the above surface active substances as inhibitors of the realization process of various mechanisms of penicillin resistance.     

Reactions of alkyl and aryl sulfides with a monocarbon platinacarbaborane anion

The reaction of the monocarbon carbaborane complex Na[Pt(PEt₃)₂(η⁵-CB₁₀H₁₁)] with some diaryl- and dialkyl disulfides has been investigated. With Ph₂S₂, two new cage substituted products are formed, [Pt(SPh)(PEt₃)(η⁵-9-SPh-7-CB₁₀H₁₀)] (1) and [Pt(SPh)(PEt₃)(η⁵-8-SPh-11-SPh-7-CB₁₀H₉)] (2), whereas with S₂ the main product is the metal substituted complex, [Pt(SBu^t)(PEt₃)(η⁵-7-CB₁₀H₁₁)] (4). All three new molecules have been identified spectroscopically (¹H, ¹³C, ³¹P, ¹¹B NMR) and through single crystal X-ray diffraction.     

Immobilization of enzymes in liquid membranes for enantioselective hydrolysis

Summary The enantioselective hydrolysis of racemic 4-acetoxy-cyclopentenone by immobilized enzymes is described. Liquid membrane emulsions were used to encapsulate the enzyme. This technique combines the specific enzymatic reaction with a selective transport through the organic phase. The product (–)-4-hydroxy-cyclopentenone was produced with an enantiomeric excess of 82%. The immobilization techniques and all reaction steps, as well as a mathematical model for the complete process are discussed in this report.     

Enzymatic synthesis of alkyl beta-D-xylosides by transxylosylation and reverse hydrolysis

The Trichoderma reesei beta-xylosidase (EC 3.2.1.37) is used to catalyze the production of alkyl beta-D-xyloside. Two general methods of production are tested and compared using the same enzyme: transglycosylation and reverse hydrolysis. Using both methods, primary, secondary, and tertiary alcohols are studied as acceptors. In kinetically controlled process (transglycosylation), the chosen donor is methyl beta-D-xyloside and primary, secondary, and tertiary alkyl alcohols are accepted. In the equilibrium-controlled synthesis, the donor is xylose whereas acceptors are only primary and secondary alcohols. The influence of the donor concentration is investigated in both processes. The yields of the kinetically controlled reactions are higher compared with those of the equilibrium-controlled synthesis. The specificity of the beta linkage is confirmed by proton nuclear magnetic resonance ((1)H NMR) analysis. (c) 1994 John Wiley & Sons, Inc.     

Enzymatically enantioselective hydrolysis of prochiral 1,3-diacyloxyglycerol derivatives.

An enzymatically enantioselective ester hydrolysis of prochiral 1,3-diacyloxy-2-substituted-2-propanol to chiral 1-acyloxy-2,3-propanediol was studied. The (R)-monoester was prepared by selection of a suitable lipase and alkyl chain length of the substrate diester. Lipase D from Rhizopus delemer gave (R)-1-isobutyryloxy-2-(2,4-difluorophenyl)-2,3-propanediol with 97%ee and 87% yield at 15 degrees C and pH 5.5. The (R)-monoester is a key intermediate of azole antifungal agents.