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A series of L-phenylalanine ionic liquids (ILs), L-tyrosine ILs, tertiary amino analogues and proposed transformation products (PTPs) have been synthesised. Antimicrobial toxicity data, as part of the green chemistry metrics evaluation and to supplement preliminary biodegradation studies, was determined for ILs, tertiary amino analogues and PTPs. Good to very good overall yields (76 to 87%) for the synthesis of 6 ILs from L-phenylalanine were achieved. A C 2 -symmetric IL was prepared from TMS-imidazole in a one-pot two-step method in excellent yield (91%). Synthesis of the L-tyrosine IL derivatives utilised a simple protection group strategy by using an extra equivalent of the bromoacetyl bromide reagent. Improvements in the synthesis of the α-bromoamide alkylating reagent from L-phenylalanine were achieved, directed by green chemistry metric analysis. A solvent switch from dichloromethane to THF is described, however the yield was 15% lower. Antimicrobial activity testing of L-phenylalanine ILs, L-tyrosine ILs, tertiary amino analogues and PTPs, against 8 bacteria and 12 fungi strains, showed that no compound had a high antimicrobial activity, apart from an L-proline analogue. In this exceptional case, the highest toxicity (IC 95 = 125 and 250 µM) was observed towards the two Gram positive strains Staphylococcus aureus and Staphylococcus epidermidis respectively. High antimicrobial activity was not found for the other bacteria or fungi strains screened. The limitations of the antimicrobial activity study is discussed in relation to SAR studies. Preliminary analysis of biodegradation data (Closed Bottle Test, OECD 301D) is presented. The pyridinium IL derivative is the preferred green IL of the series based on synthesis, toxicity and biodegradation considerations. This work is a joint study with Kümmerer and co-workers and the PTPs were selected as target compounds based on concurrent biodegradation studies by the Kümmerer group. For the comprehensive biodegradation and transformation product analysis see the accompanying paper.

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A comprehensive study devoted to designing green surface-active ionic liquids (SAILs) based on the “benign-of-design” approach results in finding greener alternatives.

3-(Substituted phenyl)-5-acyloxymethyl-2H,5H-furan-2-ones related to the natural product (-)incrustoporine were synthesized and their in vitro antifungal activity evaluated. The compounds with halogen substituents on the phenyl ring displayed much higher antifungal effect against Aspergillus fumigatus than selected representatives of azole antifungal drugs. In particular, the activity (1.34 microg/mL) of the most promising derivative, 3-(3,4-dichlorophenyl)-5-pivaloyloxymethyl-2H,5H-furan-2-one, was comparable to that of amphotericin B (0.5 microg/mL). Preliminary evaluation of the toxicity of the compound was carried out as well. Considering the size and properties of these molecules in comparison with those of amphotericin B, further development of this novel group of antifungals may lead to substances with better pharmacological profiles than that of the standard anti-Aspergillus drug.

Imidazolium derived ionic liquid catalysts have been developed which are aprotic and of low antimicrobial and antifungal toxicity, yet which can act as efficient Brønsted acidic catalysts in the presence of protic additives. The catalysts can be utilised at low loadings and can be recycled 15 times without any discernible loss of activity.Over the last decade Ionic Liquids (ILs) have been extensively investigated as potential replacements for volatile organic compounds for use as (inter alia) both tunable reaction media and catalytic solvents.