Table 1.

Compounds most widely used in H₄R investigation

Compound	Chemical name	Human H4R Ki (nmol·L−1)
Histamine	2-(1H-imidazol-5-yl)ethanamine	16
Imetit	2-(1H-imidazol-5-yl)ethyl carbamimidothioate	1.6
Clobenpropit	3-(1H-imidazol-5-yl)propyl N′-[(4-chlorophenyl)methyl]carbamimidothioate	13
OUP-16	(-)-2-cyano-1-methyl-3-{(2R,5R)-5-[1H-imidazol-4(5)-yl]tetrahydrofuran-2-yl}methyl-guanidine	125
4-Methylhistamine	2-(5-methyl-1H-imidazol-4-yl)ethanamine	50
Clozapine	3-chloro-6-(4-methylpiperazin-1-yl)-5H-benzo[c][1,5]benzodiazepine	625
VUF8430	2-(2-guandinoethyl)isothiourea	32
Thioperamide	N-cyclohexyl-4-(1H-imidazol-5-yl)piperidine-1-carbothioamide	125
JNJ7777120	1-[(5-chloro-1H-indol-2-yl)carbonyl]-4-methylpiperazine	4
VUF6002	(5-chloro-1H-benzo[d]imidazol-2-yl)(4-methylpiperazin-1-yl)methanone	26
A-987306	cis-4-(Piperazin-1-yl)-5,6,7a,8,9,10,11,11a-octahydrobenzofuro[2,3-h]quinazolin-2-amine	6
A-940894	4-piperazin-1-yl-6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d]pyrimidin-2-ylamine	71

Values (Ki) are taken from Leurs et al. (2009) except for imetit (Wulff et al., 2002) and A-940894 (Strakhova et al., 2009). More detailed information on these and other H₄R compounds is reviewed at Lim et al. (2005), Leurs et al. (2009), Lim et al. (2009), Smits et al. (2009), Koenig et al. (2010) and Smits et al. (2010).

H₄R, histamine H₄ receptor.