TABLE 5

Interaction of prototypical diterpenes with ACs 1, 2 and 5 and 5C1:2C2

AC activities were determined as described in the presence of Mn²⁺. Reaction mixtures contained diterpenes at concentrations from 100 nM–300 μM. Data were analyzed by nonlinear regression to determine the EC₅₀ values. For recombinant holo-ACs, the efficacy for each analog was determined by dividing the maximal stimulation obtained for the analog by the maximum stimulation obtained by treatment with 300 μM FSK expressed in percent. In case of 5C1:2C2, the efficacy for each analog was determined by dividing the maximal stimulation obtained for the analog by the maximum stimulation obtained by treatment with 100 μM FSK expressed in percent. Data for holo-ACs were adapted from Erdorf et al. (2011), and data for 5C1:2C2 were taken from Pinto et al. (2009).

Diterpene	AC1		AC2		AC5		5C1:2C2
Diterpene	EC₅₀	Efficacy	EC₅₀	Efficacy	EC₅₀	Efficacy	EC₅₀	Efficacy
	μM	%	μM	%	μM	%	μM	%
FSK	3.3	100	38	100	18	100	7.4	100
DMB-FSK	2.8	65	50	46	11	81	28	41
6A7DA-FSK	3.0	110	17	70	13	70	2.6	83
7DA-FSK	9.3	109	81	62	38	124	3.1	86
9d-FSK	17	98	127	30	61	108	20	79
1d-FSK	N.D.	3	N.D.	0.4	N.D.	0.7	ine.	ine.
BODIPY-FSK	1.2	73	0.2	−19	2.7	69	N.D.	N.D.

N.D., not determined. Ine., ineffective. Structures of diterpenes are shown in Fig. 12. FSK, forskolin; DMB, 7-deacetyl-7-(N-methylpiperazino-butyryloxy); 6A7DA, 6-acetyl-7-deacetyl; 7DA, 7-deacetyl; 9d, 9-deoxy; 1d, 1-deoxy; BODIPY, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene.