Table 3.

Partition coefficients of the neutral and ionized forms, and pK_a values of the tested compounds, and of metronidazole used as a control in the cellular uptake studies. Partition coefficients of the ionic forms observed at pH 7 are marked bold

Inhibitor	logPa	logDa,b	Ionic form at pH 7	pKac
Formycin A	− 1.90	− 4.64	Neutral	4.6; 9.7
Formycin B	− 2.06	− 4.63	Neutral	0.9; 8.6
Hadacidin	− 2.26	− 4.06	Anion	3.5; 9.4
Metronidazole	− 0.47	n.d	Neutral	2.38

^aCoefficients logP and logD were calculated using the Molinspiration Cheminformatics website http://www.molinspiration.com

^blogD refers to the water:octanol partition coefficient of the ionized form, namely N(4) protonated formycin A, N(6) deprotonated formycin B and hadacidin with deprotonated carboxyl group; formycin ring numbering is shown in Fig. 2

^cpK_a values and protonation sites for formycins from Giziewicz and Shugar (1977); Wierzchowski and Shugar (1982); Bzowska et al. (1992), for hadacidin from Gottlieb and Shaw (2013) and for metronidazole from Hellgren et al. (1995)