Lastly, Au4 was submitted as a mixture of non-separable, well characterized isomers (Au4a and Au4b, Figure ). The compound was submitted together with a series of metal complexes derived from bis(pirydil)allenes: a series of complexes containing the intact bis(pyridyl)allene framework (palladium(II), platinum(IV) and gold(III)), a vinyl-platinum(II) metallacycle and a series of gold(I) and gold(III) carbenes formed by the nucleophilic attack of an allenic pyridine into the allene moiety (Figure in SI). The first class of compounds with the allene in the structure have recently been reported in several catalytic applications, in their interaction with i-motif DNA and as potential anticancer agents. From this series, the free ligands (Au-Ligand1 and Au-Ligand2) as well as the platinum(IV) complexes did not show any activity against any tested strains in CO-ADD (Table in SI). The palladium(II) analogues showed good activity against MRSA and the two yeasts tested but also exhibited high levels of cytotoxicity against the mammalian cell line. The two gold(III) analogues where the allene ligands are coordinated through the pyridyl nitrogens (Au-S11 and Au-S12) showed moderate to good activity against the two fungal strains tested. Although the only difference between the two compounds is the switch from a phenyl to a tert-butyl group on the ligand framework, this is enough to go from none to high levels of haemolysis. From the second class of allenederived complexes, the vinyl-Pt(II) metallacycle showed good activity against MRSA and the two yeasts tested but also exhibited high levels of cytotoxicity against the mammalian cell line. This platinum complex and the novel gold carbenes series were originally studied for their application as potential catalysts for the cyclisation of 1,6-enynes, and no biological activity for them has been reported to date. From this series, only the gold(III) carbene Au-S13 showed some moderate activity against any of the tested Gram-negative strains as well as high activity against MRSA and yeasts. However, both Au-S13 and its gold(I) analogue, Au-S14 showed high toxicity levels, leaving only the gold(I) complex Au-S15 as an active and non-toxic analogue. This compound would have qualified for further testing, but unfortunately, we were unable to obtain more of it for this study. Similarly, the gold(III) complex Au4 showed high levels of antifungal activity across the antifungal panel while no cytotoxicity or haemolysis up to 200 µM could be detected resulting in a therapeutic index of 33,333 (Table in SI). The original sample of Au4 submitted to CO-ADD was received as a 1:2 mixture (Au4a:Au4b).