Synthesis of stereochemically-biased spiropyrans by microwave-promoted, one-pot alkylation-condensation.

A microwave-assisted, two-step, one-pot synthesis of spiropyrans has been developed. This process was used to synthesise a range of sterically-congested spiropyrans from readily available precursors, employing environmentally benign solvents. The unusual substituent pattern possessed by these structures has been shown to influence the stereoselectivity of spiropyran ring-closure.

Differential virulence of Candida glabrata glycosylation mutants.

The fungus Candida glabrata is an important and increasingly common pathogen of humans, particularly in immunocompromised hosts. Despite this, little is known about the attributes that allow this organism to cause disease or its interaction with the host immune system. However, in common with other fungi, the cell wall of C. glabrata is the initial point of contact between the host and pathogen, and as such, it is likely to play an important role in mediating interactions and hence virulence. Here, we show both through genetic complementation and polysaccharide structural analyses that C. glabrata ANP1, MNN2, and MNN11 encode functional orthologues of the respective Saccharomyces cerevisiae mannosyltransferases. Furthermore, we show that deletion of the C. glabrata Anp1, Mnn2, and Mnn11 mannosyltransferases directly affects the structure of the fungal N-linked mannan, in line with their predicted functions, and this has implications for cell wall integrity and consequently virulence. C. glabrata anp1 and mnn2 mutants showed increased virulence, compared with wild-type (and mnn11) cells. This is in contrast to Candida albicans where inactivation of genes involved in mannan biosynthesis has usually been linked to an attenuation of virulence. In the long term, a better understanding of the attributes that allow C. glabrata to cause disease will provide insights that can be adopted for the development of novel therapeutic and diagnostic approaches.

Differences in fungal immune recognition by monocytes and macrophages: N-mannan can be a shield or activator of immune recognition.

We designed experiments to assess whether fungal cell wall mannans function as an immune shield or an immune agonist. Fungal cell wall ß-(1,3)-glucan normally plays a major and dominant role in immune activation. The outer mannan layer has been variously described as an immune shield, because it has the potential to mask the underlying ß-(1,3)-glucan, or an immune activator, as it also has the potential to engage with a wide range of mannose detecting PRRs. To resolve this conundrum we examined species-specific differences in host immune recognition in the och1Δ N-mannosylation-deficient mutant background in four species of yeast-like fungi. Irrespective of the fungal species, the cytokine response (TNFα and IL-6) induced by the och1Δ mutants in human monocytes was reduced compared to that of the wild type. In contrast, TNFα production induced by och1Δ was increased, relative to wild type, due to increased ß-glucan exposure, when mouse or human macrophages were used. These observations suggest that N-mannan is not a major PAMP for macrophages and that in these cells mannan does shield the fungus from recognition of the inner cell wall ß-glucan. However, N-mannan is a significant inducer of cytokine for monocytes. Therefore the metaphor of the fungal "mannan shield" can only be applied to some, but not all, myeloid cells used in immune profiling experiments of fungal species.

New insights into the structure of (1→3,1→6)-ß-D-glucan side chains in the Candida glabrata cell wall.

ß-Glucan is a (1→3)-ß-linked glucose polymer with (1→6)-ß-linked side chains and a major component of fungal cell walls. ß-Glucans provide structural integrity to the fungal cell wall. The nature of the (1-6)-ß-linked side chain structure of fungal (1→3,1→6)-ß-D-glucans has been very difficult to elucidate. Herein, we report the first detailed structural characterization of the (1→6)-ß-linked side chains of Candida glabrata using high-field NMR. The (1→6)-ß-linked side chains have an average length of 4 to 5 repeat units spaced every 21 repeat units along the (1→3)-linked polymer backbone. Computer modeling suggests that the side chains have a bent curve structure that allows for a flexible interconnection with parallel (1→3)-ß-D-glucan polymers, and/or as a point of attachment for proteins. Based on these observations we propose new approaches to how (1→6)-ß-linked side chains interconnect with neighboring glucan polymers in a manner that maximizes fungal cell wall strength, while also allowing for flexibility, or plasticity.

New S/O-substituted ferrocenediyl ligands and their metal complexes.

New unsymmetrical S/O 1,1'-disubstituted ferrocenediyl ethers and hydroxides have been synthesised. The coordination chemistry of 1-(methylsulfanyl)-1'-(methoxy)ferrocene has been investigated with palladium(II) and platinum(II) precursors. With palladium(II), a bis-mu-chloro-bridged dimeric complex was obtained with the ligand bound solely through the thioether donor group. With platinum(II), a bis-ligand trans-sulfur ligated complex was obtained and structurally characterised.