On the halogenation of N(1),N(2)-di-t-Boc-5-hydroxy-piperazic acid esters and the conformational preferences of their 5-halo-piperazic acid products. The importance of A1,3 rotameric-strain in determining N(2)-acyl piperazic acid ring conformation

In this Letter, an unambiguous synthetic strategy is reported for the preparation of enantiomerically purecis-5-halo-piperazic acid derivatives in single diastereoisomer form. Contrary to the recent report by Shin and co-workers (Chem. Lett. 2001, 1172), in which it is claimed that the Ph₃P and N-chlorosuccinimide (NCS)-mediated chlorination of (3R,5S)-trans-N(1),N(2)-di-t-Boc-5-hydroxy-piperazic acid derivative 1proceeds with retention of configuration at C(5) to give 2, we now show that this and related Ph₃P-mediated halogenations all occur with S_N2 inversion at the alcohol center, as is customary for such reactions. Specifically, we demonstrate that the (3R,5S)-trans-5-Cl-piperazic acid derivative 2 claimed by Shin and co-workers (Chem. Lett. 2001, 1172) is in actual fact the chlorinated (3S,5R)-enantiomer 6, which must have been prepared from the cis-(3S,5S)-alcohol 3, a molecule whose synthesis is not formally described in the Shin paper. We further show here that the cis-(3R,5R)-5-Cl-Piz 13 claimed by Shin and co-workers inChem. Lett. 2001, 1172, is also (3S,5R)-trans-5-Cl-Piz 6. Authentic 13 has now been synthesized by us, for the very first time, here. Since Lindsley and Kennedy have recently utilized the now invalid Shin and co-workers’ retentive Ph₃P/NCS chlorination procedure on 1 in their synthetic approach to piperazimycin A (Tetrahedron Lett. 2010, 51, 2493), it follows that their claimed 5-Cl-Piz-containing dipeptide 25 probably has the alternate structure 26, where the 5-Cl-Piz residue has a 3,5-cis-configuration. The aforementioned stereochemical misassignments appear to have come from a mix-up of starting materials by Shin and co-workers (Chem. Lett. 2001, 1172), and an under-appreciation of the various steric and conformational effects that operate in N(2)-acylated piperazic acid systems, most especially rotameric A^1,3-strain. The latter has now been unambiguously delineated and defined here under the banner of the A^1,3-rotamer effect.

UDP-galactose 4'-epimerase from the liver fluke, Fasciola hepatica: biochemical characterization of the enzyme and identification of inhibitors

Leloir pathway enzyme uridine diphosphate (UDP)-galactose 4'-epimerase from the common liver fluke Fasciola hepatica (FhGALE) was identified and characterized. The enzyme can be expressed in, and purified from, Escherichia coli. The recombinant enzyme is active: the K(m) (470 μM) is higher than the corresponding human enzyme (HsGALE), whereas the k(cat) (2.3 s(-1)) is substantially lower. FhGALE binds NAD(+) and has shown to be dimeric by analytical gel filtration. Like the human and yeast GALEs, FhGALE is stabilized by the substrate UDP-galactose. Molecular modelling predicted that FhGALE adopts a similar overall fold to HsGALE and that tyrosine 155 is likely to be the catalytically critical residue in the active site. In silico screening of the National Cancer Institute Developmental Therapeutics Program library identified 40 potential inhibitors of FhGALE which were tested in vitro. Of these, 6 showed concentration-dependent inhibition of FhGALE, some with nanomolar IC50 values. Two inhibitors (5-fluoroorotate and N-[(benzyloxy)carbonyl]leucyltryptophan) demonstrated selectivity for FhGALE over HsGALE. These compounds also thermally destabilized FhGALE in a concentration-dependent manner. Interestingly, the selectivity of 5-fluoroorotate was not shown by orotic acid, which differs in structure by 1 fluorine atom. These results demonstrate that, despite the structural and biochemical similarities of FhGALE and HsGALE, it is possible to discover compounds which preferentially inhibit FhGALE.

Clinical potential of gene-directed enzyme prodrug therapy to improve radiation therapy in prostate cancer patients

Despite the advances in prostate cancer diagnosis and treatment, current therapies are not curative in a significant proportion of patients. Gene-directed enzyme prodrug therapy (GDEPT), when combined with radiation therapy, could improve the outcome of treatment for prostate cancer, the second leading cause of cancer death in the western world. GDEPT involves the introduction of a therapeutic transgene, which can be targeted to the tumour cells. A prodrug is administered systemically and is converted to its toxic form only in those cells containing the transgene, resulting in cell kill. This review will discuss the clinical trials which have investigated the potential of GDEPT at various stages of prostate cancer progression. The advantages of using GDEPT in combination with radiotherapy will be examined, as well as some of the recent advances which enhance the potential utility of GDEPT.

A nitrile-metabolising enzyme and a process for producing an acid using same

The present invention relates to an isolated nucleotide sequence and corresponding polypeptide derived from the nitrile-metabolising Pantoea strain deposited under NCIMB 41854. Said isolated polypeptide acts as a nitrilase and the invention extends to a process for producing a carboxylic acid using said isolated polypeptide to metabolise nitriles such as 3-hydroxyglutaronitrile, 3-hydroxybutyronitrile and 3- hydroxy-phenylpropionitrile to form corresponding carboxylic acids.

GTPase activity of dynamin and resulting conformation change are essential for endocytosis

Dynamin is a large GTPase with a relative molecular mass of 96,000 (Mr 96K) that is involved in clathrin-mediated endocytosis and other vesicular trafficking processes. Although its function is apparently essential for scission of newly formed vesicles from the plasma membrane, the nature of dynamin's role in the scission process is still unclear. It has been proposed that dynamin is a regulator (similar to classical G proteins) of downstream effectors. Here we report the analysis of several point mutants of dynamin's GTPase effector (GED) and GTPase domains. We show that oligomerization and GTP binding alone, by dynamin, are not sufficient for endocytosis in vivo. Rather, efficient GTP hydrolysis and an associated conformational change are also required. These data argue that dynamin has a mechanochemical function in vesicle scission.

Placental antioxidant enzyme status and lipid peroxidation in pregnant women with type 1 diabetes: The effect of vitamin C and E supplementation

AIM: In view of the increased rates of pre-eclampsia observed in diabetic pregnancy and the lack of ex vivo data on placental biomarkers of oxidative stress in T1 diabetic pregnancy, the aim of the current investigation was to examine placental antioxidant enzyme status and lipid peroxidation in pregnant women with type 1 diabetes. A further objective of the study was to investigate the putative impact of vitamin C and E supplementation on antioxidant enzyme activity and lipid peroxidation in type 1 diabetic placentae.

METHODS: The current study measured levels of antioxidant enzyme [glutathione peroxidase (Gpx), glutathione reductase (Gred), superoxide dismutase (SOD) and catalase] activity and degree of lipid peroxidation (aqueous phase hydroperoxides and 8-iso-prostaglandin F2α) in matched central and peripheral samples from placentae of DAPIT (n=57) participants. Levels of vitamin C and E were assessed in placentae and cord blood.

RESULTS: Peripheral placentae demonstrated significant increases in Gpx and Gred activities in pre-eclamptic in comparison to non-pre-eclamptic women. Vitamin C and E supplementation had no significant effect on cord blood or placental levels of these vitamins, nor on placental antioxidant enzyme activity or degree of lipid peroxidation in comparison to placebo-supplementation.

CONCLUSION: The finding that maternal supplementation with vitamin C/E does not augment cord or placental levels of these vitamins is likely to explain the lack of effect of such supplementation on placental indices including antioxidant enzymes or markers of lipid peroxidation.

Enzyme-catalysed oxidation of 1,2-disulfides to yield chiral thiosulfinate, sulfoxide and cis-dihydrodiol metabolites

Enantioenriched and enantiopure thiosulfinates were obtained by asymmetric sulfoxidation of cyclic 1,2-disulfides, using chemical and enzymatic (peroxidase, monooxygenase, dioxygenase) oxidation methods and chiral stationary phase HPLC resolution of racemic thiosulfinates. Enantiomeric excess values, absolute configurations and configurational stabilities of chiral thiosulfinates were determined. Methyl phenyl sulfoxide, benzo[c]thiophene cis-4,5-dihydrodiol and 1,3-dihydrobenzo[c]thiophene derivatives were among unexpected types of metabolites isolated, when acyclic and cyclic 1,2-disulfide were used as substrates for Pseudomonas putida strains. Possible biosynthetic pathways are presented for the production of metabolites from 1,4-dihydrobenzo-2,3-dithiane, including a novel cis-dihydrodiol metabolite that was also derived from benzo[c]thiophene and 1,3-dihydrobenzo[c]thiophene.

CGRP-cleavage enzyme detection using a biotinylated hydroxymate affinity probe

Introduction: Neuropeptides contribute to the pathophysiology of peripheral inflammation and a neurogenic component has been described for many inflammatory diseases, including periodontitis. Neuropeptides are susceptible to cleavage by peptidases and therefore the exact location and level of expression of peptidases are major determinants of neuropeptide action. Previous studies by our research group suggested that levels of the neuropeptide calcitonin gene-related peptide (CGRP) may be regulated by peptidases present in gingival crevicular fluid (GCF). Objectives: The aim of this work was to purify and partially characterize the GCF enzyme responsible for CGRP degradation using a biotinylated hydroxymate affinity probe (based on the P1-P4 amino acid sequence of the observed cleavage site) which we previously showed to inhibit CGRP degradation. Methods: Pooled healthy and pooled periodontitis GCF samples were subject to a pre-clear step with magnetic streptavadin beads. Healthy and diseased samples were incubated with the biotinylated hydroxymate probe (20 uM) after which biotinylated proteins were purified from the sample using magnetic streptavadin beads. Bound proteins were subjected to SDS-PAGE and western blotting. Biotin incorporated proteins were disclosed using a streptavadin horse radish peroxidase conjugate. Results: A band was disclosed in the periodontitis pooled sample at a molecular weight of approximately 60 kDa. The band was absent in the pooled healthy samples. As expected, when periodontitis samples were pre-boiled to denature proteins before the addition of the hydroxymate probe, no biotin incorporated band was present. Conclusions: This work demonstrates the purification and disclosure of a protein found specifically in periodontitis which binds to the specific biotinylated hydroxymate affinity probe based on the cleavage site of CGRP only when in its native form. We intend to scale up the sample size thus allowing the identification of the putative CGRP degrading peptidase using MALDI-mass spectrometry.
Funded by an IADR/GlaxoSmithKline Innovation in Oral Care Award