Synthesis of C-8 Deuterated Glycosides of 3-Deoxy-D-manno-oct-2-ulosonic Acid (Kdo) Related to Chlamydial Lipopolysaccharides

Summary.  Methyl glycosides of Kdo and a (2→8)-linked Kdo disaccharide were prepared which contain a deuterium label at C-8 of the reducing unit. The label was introduced in fair diastereoselectivity upon reduction of an aldehyde group using a chiral borane complex derived from N-benzyloxycarbonyl-(S)-proline which produced the 8-(S)-deuterated derivative as the major isomer. Further coupling with a Kdo bromide gave the α-(2→8)-linked disaccharide in good yield. The deprotected disaccharide serves as a model for NMR spectroscopic studies on the side chain conformation of a carbohydrate epitope from the bacterial pathogen Chlamydia. Received September 17, 2001. Accepted October 17, 2001     

Synthesis and purity assessment of tetra- and pentaacyl lipid A of Chlamydia containing (R)-3-hydroxyicosanoic acid

Based on structural data of lipid A from Chlamydia trachomatis strains, chemically pure tetra- and pentaacyl 1,4′-bisphosphoryl as well as the related 4′-monophosphoryl derivatives of lipid A were synthesized. (R)-3-Hydroxyicosanoic acid as a chiral constituent was prepared via Noyori-reduction of methyl-3-oxoicosanoic acid. Synthetic intermediates were O-acylated with myristoic acid residues at positions 3 and 3′ and N-acylated with (R)-3-hydroxyicosanoic acid at both glucosamine units. Efficient purification methods for highly hydrophobic long-chain tri-, tetra- and pentaacyl progenitors of lipid A have been developed. Purity and homogeneity of the synthetic target compounds were confirmed by NMR and MS-data as well as a sensitive immunostaining approach. The tetra- and pentaacyl species serve as biomedical probes to investigate the endotoxic potential of chlamydial lipid A and to clarify its role in Chlamydia associated infections.     

Stereochemical basis for the anti-chlamydial activity of the phosphonate protease inhibitor JO146

JO146, a mixture of two diastereomers of a peptidic phosphonate inhibitor for Chlamydial HtrA (CtHtrA), has reported activity against Chlamydia species in both human and koala. In this study we isolated the individual diastereomers JO146-D1 and JO146-D2 (in ≥90% purity) and assessed their individual inhibitory activity against the serine protease human neutrophil elastase (HNE) which is structurally and functionally related to CtHtrA, as well as in Chlamydia trachomatis cell culture. JO146-D2 [S,S,R-Boc-Val-Pro-Val^P(OPh)₂], the isomer with the physiologically relevant valine at P1, had an approximate 2.5 – fold increase in in vitro HNE inhibition potency over JO146-D1 [S,S,S-Boc-Val-Pro-Val^P(OPh)₂] and greater than 100 – fold increase in cellular anti-chlamydial activity compared to JO146-D1 which possesses the unnatural valine at P1. JO146 and the individual diastereomers had excellent selectivity for the serine protease HNE over the potential off-target serine proteases trypsin and chymotrypsin. Docking studies supported the biological data with a geometrically unfavoured interaction observed between the P1 valine residue of JO146-D1 and the enzyme S1 sub-pocket.     

Re-infection-induced backward bifurcation in the transmission dynamics of Chlamydia trachomatis

A new two-group deterministic model for Chlamydia trachomatis is designed and analyzed to gain insights into its transmission dynamics. The model is shown to exhibit the phenomenon of backward bifurcation, where a stable disease-free equilibrium (DFE) co-exists with one or more stable endemic equilibria when the associated reproduction number is less than unity. It is further shown that the backward bifurcation dynamic is caused by the re-infection of individuals who recovered from the disease. The epidemiological implication of this result is that the classical requirement of the reproduction number being less than unity becomes only a necessary, but not sufficient, condition for disease elimination. The basic model is extended to incorporate the use of treatment for infectious individuals (including those who show disease symptoms and those who do not). Rigorous analysis of the treatment model reveals that the use of treatment could have positive or negative population-level impact, depending on the sign of a certain epidemiological threshold. The treatment model is used to evaluate various treatment strategies, namely treating every infected individual showing symptoms of Chlamydia (universal strategy), treating only infectious males showing Chlamydia symptoms (male-only strategy) and treating only infectious females showing symptoms of Chlamydia (female-only strategy). Numerical simulations show that the implementation of the male-only or female-only strategy can induce an indirect benefit of saving new cases of Chlamydia infection in the opposite sex. Further, the universal strategy gives the highest reduction in the cumulative number of new cases of infection.     

Combining discrete-event simulation and system dynamics in a healthcare setting: A composite model for Chlamydia infection

This paper presents a composite model in which two simulation approaches, discrete-event simulation (DES) and system dynamics (SD), are used together to address a major healthcare problem, the sexually transmitted infection Chlamydia. The paper continues an on-going discussion in the literature about the potential benefits of linking DES and SD. Previous researchers have argued that DES and SD are complementary approaches and many real-world problems would benefit from combining both methods. In this paper, a DES model of the hospital outpatient clinic which treats Chlamydia patients is combined with an SD model of the infection process in the community. These two models were developed in commercial software and linked in an automated fashion via an Excel interface. To our knowledge this is the first time such a composite model has been used in a healthcare setting. The model shows how the prevalence of Chlamydia at a community level affects (and is affected by) operational level decisions made in the hospital outpatient department. We discuss the additional benefits provided by the composite model over and above the benefits gained from the two individual models.