title: Non-Imidazole Histamine H3 Ligands. Part VI. Synthesis and Preliminary Pharmacological Investigation of Thiazole-Type Histamine H3-Receptor Antagonists with Lacking a Nitrogen Nucleus in the Side Chain.
abstract: BACKGROUND
  Antagonists to the H3 receptor are considered to be potential drugs for the treatment of Alzheimer's disease, attention deficit-hyperactive disorder, memory and learning deficits, and epilepsy. The initial development of potent H3 receptor antagonists focused on extensive modification of the natural ligand histamine. However, it has appeared that imidazole-containing ligands are associated with inhibition of cytochrome P450 enzymes, caused by imidazole nitrogen complexation to heme iron in the active site of the enzyme. For these reasons, the development of potent non-imidazole H3receptor antagonists was eagerly awaited.
  
  
  OBJECTIVE
  Previously, we reported the synthesis and pharmacological in vitro characterization of series of potent histamine H3receptor non-imidazole antagonists belonging to the class of substituted 2-thiazol-4-n-propylpiperazines. A lead compound 1 of this family was a derivative carrying the ethylaminomethylpropyl chain.
  
  
  METHODS
  With the aim of increasing lipophilicity, that will help the ligands to cross the blood-brain barrier, we synthesized a series of new 2-thiazol-4-n-propylpiperazines where the ethylaminomethylpropyl moiety was replaced by a p-substituted-, an unsubstituted benzene ring, and ω-phenylalkyl substituent at positions 4 and 5 of thiazole ring, respectively. All compounds were tested for H3 antagonistic effects in vitro using the electrically contracting guinea pig jejunum.
  
  
  RESULTS
  The most active compounds of presented series 3d, 3e, and 3j showed lower affinity than the lead compound 1 and additionally, derivatives 3d and 3j possessed weak, competitive H1 antagonistic activity. This is in contrast to the lead compound 1 that has no affinity at H1 receptor.
  
  
  CONCLUSIONS
  We can conclude that a side chain in the 2-thiazol-4-n-propylpiperazine scaffold should contain a basic center and should be present at a favorable position 5 of thiazole ring.
authors.forename: Roman
authors.initials: R
authors.lastname: Guryn
authors.forename: Marek
authors.initials: M
authors.lastname: Staszewski
authors.forename: Piotr
authors.initials: P
authors.lastname: Kopczacki
authors.affiliation: Department of Synthesis and Technology of Drugs, Medical University, Muszynskiego Street 1, 90-145 Lódz, Poland.. Poland.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Walczyski
mesh_terms: D004305:Dose-Response Relationship, Drug; D054828:Histamine H3 Antagonists / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D008024:Ligands; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D018100:Receptors, Histamine H3 / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013844:Thiazoles / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D054828:Histamine H3 Antagonists; D008024:Ligands; D018100:Receptors, Histamine H3; D013844:Thiazoles; D009584:Nitrogen
keywords: Histamine H3receptor/non-imidazole H3 antagonists/ 1-(2-thiazol-4-yl)- and 1-(2-thiazol-5-yl)-4-npropylpiperazines.