Table 5.

Structure–activity relationships of β-carboline compounds that enhanced the production of RMs: Modification of tetrahydro β-carboline compounds. Streptomyces sp. SN-593 was cultured separately in the presence of 1 µg ml⁻¹ of each compound. RM production was measured by LC analysis. The data shown are expressed as the mean ± SD from 3 experiments.

Compound	R1	R2	R3	RMs mg l−1
12a	H	COOH	H	0.69 ± 0.59
12b	H	CONH2	H	2.16 ± 1.24
12c	H	COOH	CH2OH	4.54 ± 1.82
12d	H	CONH2	CH2OH	4.16 ± 0.25
12e		CONH2	H	4.52 ± 1.27
12f		COOH	H	2.41 ± 0.18