Table 1.

Considered carnosine derivatives 1–10 and their CA activating properties against human CA isoforms hCA I, II, VA and IX, by a stopped-flow CO₂ hydrase assay. Histamine 11 was used as reference standard activator.

No.	Compound	R	R1	X	n	KA (µM) *
						hCA I	hCA II	hCA VA	hCA IX
1	l-carnosine	COOH	H	H	2	92.1	83.4	17.2	46.3
2	d-carnosine	COOH	H	H	2	54.3	76.6	8.93	10.1
3	l-carnosinamide	CONH2	H	H	2	45.2	91.5	18.5	4.71
4	d-carnosinamide	CONH2	H	H	2	16.6	>100	16.1	45.5
5	l-homocarnosine	COOH	H	H	3	77.0	88.9	51.3	7.35
6	l-anserine	COOH	H	1-Me	2	80.4	93.7	17.4	1.14
7	l-balenine	COOH	H	3-Me	2	20.7	>100	47.2	50.2
8	carcinine	H	H	H	2	16.6	>100	6.4	38.0
7	Gly-l-His	COOH	H	H	1	31.9	90.1	9.83	11.5
8	Gly-Gly-l-His	COOH	Gly	H	1	74.3	>100	52.8	19.4
9	N-acetyl-X-carnosine	COOH	Acetyl	H	2	79.6	102	47.1	32.6
10	l-carnosinol	CH2OH	H	H	2	28.3	>100	12.2	20.5
11	histamine	-	-	-	-	2.1	125	0.010	35.1

* Mean from three different assays (errors in the range of ± 10% of the reported values, data not shown).