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K Faber

Publications and source records attributed to K Faber.

At least 19 recordsLinked to original sources
PubMed2006

Biocatalytic approaches for the quantitative production of single stereoisomers from racemates.

Strategies for the chemoenzymatic transformation of a racemate into a single stereoisomeric product in quantitative yield have been developed. A range of industrially relevant alpha-hydroxycarboxylic acids was deracemized in a stepwise fashion via lipase-catalysed enantioselective O-acylation, followed by mandelate racemase-catalysed racemization of the remaining non-reacted substrate enantiomer. Alternatively, aliphatic alpha-hydroxycarboxylic acids were enzymatically isomerized using whole resting cells of Lactobacillus spp. Enantioselective hydrolysis of rac-sec-alkyl sulphate esters was accomplished using novel alkyl sulphatases of microbial origin. The stereochemical path of catalysis could be controlled by choice of the biocatalyst. Whereas Rhodococcus ruber DSM 44541 and Sulfolobus acidocaldarius DSM 639 act through inversion of configuration, stereo-complementary retaining sulphatase activity was detected in the marine planctomycete Rhodopirellula baltica DSM 10527.

Animals↗
PubMed2001

Assisted reproductive interventions and multiple birth.

OBJECTIVE: To investigate the contributions of ovulation-inducing drugs and assisted reproductive technologies to multiple birth. METHODS: This historic prospective study was conducted in a cohort of 13,151 women who delivered after 20 weeks' gestation between October 1996 and December 1999. The study setting was a Colorado health maintenance organization. Cases were women who were pregnant as a result of exposure to treatment with either assisted reproductive technologies or ovulation induction in the absence of assisted reproductive technologies. The main outcome measure was multiple birth. RESULTS: There was a significant association between assisted conception and multiple birth. Compared with women with naturally conceived pregnancies, there was a 25-fold likelihood (95% confidence interval 18, 35, P <.001) of multiple birth among women exposed to any of those treatments. In the total cohort the proportion of multiple births attributable to those treatments was 33%. After adjusting for the use of assisted conception and other covariates, we found no association between advanced maternal age and multiple birth. CONCLUSION: In this cohort, assisted reproductive interventions were strongly associated with multiple birth. Although a higher proportion of older women sought assisted reproductive technologies, we did not find an independent relationship between advanced maternal age and multiple birth. The increasing number of multiple births attributable to assisted conception raises public health concerns regarding multiple gestation-related maternal and infant morbidities.

Adolescent↗
PubMed2001

Microbial epoxide hydrolases for preparative biotransformations.

Epoxide hydrolases from microbial sources are highly versatile biocatalysts for the asymmetric hydrolysis of epoxides on a preparative scale. Besides kinetic resolution, which furnishes the corresponding vicinal diol and remaining non-hydrolysed epoxide in nonracemic form, enantioconvergent processes are possible: these are highly attractive as they lead to the formation of a single enantiomeric diol from a racemic oxirane. The data accumulated over recent years reveal a common picture of the substrate structure selectivity pattern of microbial epoxide hydrolases and indicate that substrates of various structural types can be selectively hydrolysed with enzymes from certain microbial sources.

Bacterial Proteins↗
PubMed1999

Determination of absolute configuration in 4-aryl-3, 4-dihydro-2(1H)-pyrimidones by high performance liquid chromatography and CD spectroscopy.

The absolute configuration of three 4-aryl-3, 4-dihydro-2(1H)-pyrimidones (Biginelli compounds, DHPMs) was established by comparison of the typical circular dichroism (CD) spectra of individual enantiomers with reference samples of known absolute configuration. The enantiomers were obtained by semipreparative separation of racemic mixtures on a Chiralcel OD-H chiral stationary phase. The method was used to establish the enantiopreference of various lipases in biocatalytic kinetic resolution experiments employing activated DHPM esters.

Chromatography, High Pressure Liquid↗
PubMed1999

Epoxide hydrolases and their synthetic applications.

Chiral epoxides and 1,2-diols, which are central building blocks for the asymmetric synthesis of bioactive compounds, can be obtained by using enzymes--i.e. epoxide hydrolases--which catalyse the enantioselective hydrolysis of epoxides. These biocatalysis have recently been found to be more widely distributed in fungi and bacteria than previously expected. Sufficient sources from bacteria, such as Rhodococcus and Nocardia spp., or fungi, as for instance Aspergillus and Beauveria spp., have now been identified. The reaction proceeds via an SN2-specific opening of the epoxide, leading to the formation of the corresponding trans-configured 1,2-diol. For the resolution of racemic monosubstituted and 2,2- or 2,3-disubstituted substrates, various fungi and bacteria have been shown to possess excellent enantioselectivities. Additionally, different methods, which lead to the formation of the optically pure product diol in a chemical yield far beyond the 50% mark (which is intrinsic to classic kinetic resolutions), are discussed. In addition, the use of non-natural nucleophiles such as azides or amines provides access to enantiomerically enriched vicinal azido- and amino-alcohols. The synthetic potential of these enzymes for asymmetric synthesis is illustrated with recent examples, describing the preparation of some biologically active molecules.

Epoxide Hydrolases↗
PubMed1999

Stereoselectivities of microbial epoxide hydrolases.

Epoxide hydrolases from bacterial and fungal sources are highly versatile biocatalysts for the asymmetric hydrolysis of epoxides on a preparative scale. Besides kinetic resolution, which yields the corresponding enantiomerically enriched vicinal diol and the remaining nonconverted epoxide, enantioconvergent processes are also possible, which lead to the formation of a single enantiomeric diol from a racemic oxirane. The data available to date indicate that the enantioselectivities of enzymes from certain microbial sources can be correlated to the substitutional pattern of various types of substrates: red yeasts (e.g. Rhodotorula or Rhodosporidium sp.) give best enantioselectivities with monosubstituted oxiranes; fungal cells (e.g. from Aspergillus and Beauveria sp.) are best suited for styrene oxide-type substrates; bacterial enzymes, on the other hand (in particular from Actinomycetes such as Rhodococcus and Nocardia sp.) are the biocatalysts of choice for more highly substituted 2,2- and 2,3-disubstituted epoxides.

Bacteria↗
PubMed1999

Compartment pressure monitoring during anterior cruciate ligament reconstruction.

A prospective double blind randomized study was carried out using 20 healthy males with anterior cruciate ligament (ACL) insufficiency undergoing bone-patellar tendon-bone ACL reconstruction. The subjects were randomized into either water or saline irrigation and then underwent identical reconstructive procedures using an arthroscopic pump. Continuous preoperative, intraoperative, and postoperative pressures were monitored using the slit catheter technique. Blood pressure and compartment pressure measurements were continuously recorded and noted at all stages of the procedure. Mean preoperative anterior and posterior compartment pressures were similar in both groups. No significant differences were noted between the anterior and posterior compartments of each group. No difference between water and saline irrigation was identified throughout the procedure. In both groups, postoperative pressures were slightly lower in the anterior and posterior compartments compared with preoperative pressures, but not significantly.

Adolescent↗
PubMed1998

Detection of a new enzyme for stereoselective hydrolysis of linalyl acetate using simple plate assays for the characterization of cloned esterases from Burkholderia gladioli.

Plate assays were developed for the identification of specific hydrolytic activities of esterases from Burkholderia gladioli, cloned and expressed in Escherichia coli. Clones showing different substrate specificities were identified by fluorescence or azo-dye formation caused by the released alcohol moiety of the hydrolyzed substrates, or by colour change of pH indicators mediated by decreased pH. The use of 1-hydroxypyrene-3,6,8-trisulfonic acid (HPTS-) esters and linalyl acetate for these assays clearly allowed to discriminate substrate specificities for two different cloned esterases, EP6 and EP10. Long chain fatty acid HPTS-esters were only hydrolyzed by the EP10 clone. On the other hand, the EP6 clone showed significant activity in hydrolysis of the sterically hindered ester linalyl-acetate. Enantioselective hydrolysis of linalyl acetate could be verified with a crude EP6 preparation on a preparative scale.

Burkholderia↗
PubMed1998

Purification and characterization of a highly selective epoxide hydrolase from Nocardia sp. EH1.

A highly enantioselective, soluble epoxide from Nocardia sp. EH1 was purified to homogeneity via a four-step procedure: (i) hydrophobic interaction chromatography on Phenyl Sepharose CL-4B, (ii) anion exchange chromatography on SOURCE 30Q, followed by (iii) a second hydrophobic interaction chromatography on Phenyl Sepharose HP, and finally (iv) gel-filtration on Superdex 75 HR 10/30. The pure protein was shown to be a monomer of integral of 34 kDa possessing an optimum pH of 8-9. Neither UV-absorbing cofactors nor metal ions were required for activity. In contrast to whole-cell activity, the partially purified enzyme proved to be considerably less stable. Stabilization was achieved by addition of non-ionic detergents such as Tween 80 or Triton X-100, causing a shift of the temperature optimum from 35 to 40 degrees C. Both effects combined led to an enhancement of the relative activity of up to approximately 150% of that of the native enzyme.

Biotechnology↗
PubMed1996

Enantiomeric perylene-glycerolipids as fluorogenic substrates for a dual wavelength assay of lipase activity and stereoselectivity.

A new type of fluorogenic alkyldiacyl glycerols was synthesized and used as fluorogenic substrates for the analysis of lipase activities and stereoselectivities. These compounds contain perylene as a fluorophore and the trinitrophenylamino (TNP) residue as a quencher. Both substituents are covalently bound to the omega-ends of the sn-2 and sn-1 (3) acyl chains, respectively. Upon glycerolipid hydrolysis, the residues are separated from each other thus allowing determination of lipase activity by the continuous increase in fluorescence intensity which is caused by dequenching. Using enantiomeric pairs of these compounds, we were able to analyze lipase stereoselectivity depending on the reaction medium. Mixtures of enantiomeric fluorogenic alkyldiacyl glycerols, selectively labelled with pyrene or perylene as fluorophores, can be used for a dual-wavelength "stereoassay" of lipases. Since absorption and emission maxima of both labels are clearly separated, hydrolysis of the respective enantiomeric substrates can be determined simultaneously, and the difference in the rates of hydrolysis can be taken as a parameter for the stereopreference of a lipase. Hydrolysis rates measured with perylene-substituted lipids are generally lower than those obtained with the pyrene analogs. Thus, with a mixture of perylene and pyrene-substituted lipids, we observe a higher apparent stereoselectivity of lipases since we measure a combination of stereo- and substrate selectivity. In the presence of albumin, all microbial lipases tested so far exhibit stereopreference for the sn-1 glycerol position. In our assay, the apparent stereoselectivities are highest if in the presence of albumin, the sn-1 position carries pyrene and the sn-3 position is substituted with perylene. The lipase stereoselectivity assay described here requires the simultaneous measurement of the fluorescence intensities at two different wavelengths in a single cuvette and can thus be carried out using existing and cheap instrumentation that was developed for the fluorimetric analysis of Ca+2 concentrations.

Animals↗
PubMed1996

Evaluation of the developmental neuroendocrine and reproductive toxicology of aluminium.

Two experiments evaluating functional endpoints pertaining to the developmental neuroendocrine effects of aluminum in the rat are reported. A total of 31 timed mated dams were fed by daily gastric gavage 0, 5, 25, 50, 250, 500 or 1000 mg/kg body weight/day aluminum as a solution of aluminum lactate in distilled water from days 5 to 15 of gestation. The 390 offspring were evaluated for morphological and physiological parameters of reproductive functioning, including birth weight, anogenital distance (AGD), timing of vaginal opening, regularly of oestrous cycles, duration of pseudopregnancy (PSP), number of superovulated oocytes, and gonadal weight. No consistent or reproducible findings suggestive of toxic effect were found in the parameters of birth weight, AGD, timing of vaginal opening, duration of PSP, number of superovulated oocytes, and adult gonadal weight. A temporary increase in the proportion of aberrant oestrous cycles was detected during the first four cycles after vaginal opening, in the 250 mg/body weight/day group, with none by the fifth consecutive oestrous cycle. These results suggest that, apart from a transient disturbance of oestrous cycle regularity, aluminum does not have a developmental reproductive toxic effect.

Administration, Oral↗
PubMed1995

Inversion of lipase stereospecificity for fluorogenic alkyldiacyl glycerols. Effect of substrate solubilization.

We synthesized enantiomeric 1-O-alkyl-2,3-diacyl-sn-glycerol and 3-O-alkyl-1,2-diacyl-sn-glycerol containing pyrene as a fluorescent reporter and the trinitrophenylamino residue as a fluorescence quencher; both reporter groups were covalently bound to the omega end of the acyl chains at positions sn-2 and sn-3(1), respectively. The fluorescence of the intact substrate molecules was very low. Chemical or enzymic release of the fatty acyl chains lead to fluorescence dequenching. The rate of lipolysis could be measured from the time-dependent increase in fluorescence intensity. We used the respective substrates for the continuous determination of activity and stereopreference of four different microbial lipases from Chromobacterium viscosum, Candida rugosa, Pseudomonas sp., Rhizopus arrhizus, as well as cutinase from Fusarium solani and lipoprotein lipase from bovine milk. The stereopreference of the lipases depended, in general, on how the substrate was solubilized in the reaction medium. All lipases under investigation preferentially hydrolysed the sn-1 acyl ester bond, if the lipid analog was dispersed in albumin-containing Tris/HCl buffer in the absence of detergent or organic solvent. In mixtures of 1:1 (by vol.) water/ethanol, the enzymes showed higher activity toward the sn-3 acyl ester bond, except for lipoprotein lipase which preferred the sn-1 acyl isomer under all conditions tested. Different stereopreferences were observed with the different lipases if the substrate was solubilized by amphiphiles (micelles of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate). C. rugosa lipase and F. solani cutinase showed high stereopreference for the sn-3 acyl ester, whereas Pseudomonas sp. lipase and C. viscosum lipase hydrolysed both enantiomers at similar rates. From spectroscopic studies, it can be inferred that the conformation of the fluorescent lipids is probably similar in water, mixtures of water and organic solvents, and in micelles. The possible effects of reaction conditions on substrate accessibility and enzyme conformation on stereoselectivity of the respective lipases are discussed.

Diglycerides↗
PubMed1993

Prospects for the increased application of biocatalysts in organic transformations.

Predicting the future use of biocatalysts for the transformation of organic compounds--both natural substrates and other compounds--needs to take many factors into account. To date, relatively few biotransformations have been developed to the industrial scale, primarily because there has been little economic incentive to replace existing successful processes with biocatalysts, with their inherent problems of instability, lack of selectivity and narrow operational range. However, advances that improve biocatalyst performance, coupled with the increasing emphasis on 'chirotechnology', are driving the development of biocatalysis as a complementary, if not a rival technology to existing chemical approaches.

Biotechnology↗
PubMed1990

Strategies for the chemoenzymatic preparation of optically active 1-alkyn-3-ols.

A series of (R)- and (S)-1-alkyn-3-ols, chiral building units for the synthesis of leukotrienes and pheromones, were prepared via enantioselective hydrolysis of their racemic esters. While the majority of biocatalysts employed (lipases, fermenting or freeze-dried microorganisms) failed in discriminating between enantiomers, lyophilized cells of baker's yeast (Saccharomyces cerevisiae Hansen) gave (S)-1-alkyn-3-ols and their corresponding (R)-esters with greater than 90% e.e.

Alcohols↗