Acyloxybutadiene tricarbonyl iron complexes as enzyme-triggered CO-releasing molecules (ET-CORMs): a structure-activity relationship studyElectronic supplementary information (ESI) available: Full experimental and spectroscopic data of all compounds. Detailed description of CO-releasing experiments, Crystallographic Data. CCDC 872868-872874. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt30662j

A series of η 4 -acyloxycyclohexadiene-Fe(CO) 3 complexes was prepared and fully characterized by spectroscopic methods including single crystal X-ray diffraction. For this purpose a new synthetic access to differently acylated 1,3- and 1,5-dienol-Fe(CO) 3 complexes was developed. The enzymatically triggered CO release from these compounds was monitored (detection of CO through GC and/or by means of a myoglobin assay) and the anti-inflammatory effect of the compounds was assessed by a cellular assay based on the inhibition of NO-production by inducible NO synthase (iNOS). It was demonstrated that the properties (rate of esterase-triggered CO release, iNOS inhibition, cytotoxicity) of the complexes strongly depend on the substitution pattern of the π-ligand and the nature of the acyloxy substituent. On enzymatic cleavage of the ester function, acyloxydiene-Fe(CO) 3 complexes are converted into oxidation-sensitive enol complexes acting as CO-releasing molecules.