Comparison of the binding of 3-fluoromethyl-7-sulfonyl-1,2,3,4-tetrahydroisoquinolines with their isosteric sulfonamides to the active site of phenylethanolamine N-methyltransferase.
3-Fluoromethyl-7-(N-substituted aminosulfonyl)-1,2,3,4-tetrahydroisoquinolines (14, 16, and 18-22) are highly potent and selective inhibitors of phenylethanolamine N-methyltransferase (PNMT). Molecular modeling studies with 3-fluoromethyl-7-(N-alkyl aminosulfonyl)-1,2,3,4-tetrahydroisoquinolines, such as 16, suggested that the sulfonamide -NH- could form a hydrogen bond with the side chain of Lys57. However, SAR studies and analysis of the crystal structure of human PNMT (hPNMT) in complex with 7 indicated that the sulfonamide oxygens, and not the sulfonamide -NH-, formed favorable interactions with the enzyme. Thus, we hypothesized that replacement of the sulfonamide -NH- with a methylene group could result in compounds that would retain potency at PNMT and that would have increased lipophilicity, thus increasing the likelihood they will cross the blood brain barrier. A series of 3-fluoromethyl-7-sulfonyl-1,2,3,4-tetrahydroisoquinolines (23-30) were synthesized and evaluated for their PNMT inhibitory potency and affinity for the alpha2-adrenoceptor. A comparison of these compounds with their isosteric sulfonamides (14, 16, and 18-22) showed that the sulfones were more lipophilic but less potent than their corresponding sulfonamides. Sulfone 24 (hPNMT Ki = 1.3 microM) is the most potent compound in this series and is quite selective for PNMT versus the alpha2-adrenoceptor, but 24 is less potent than the corresponding sulfonamide, 16 (hPNMT Ki = 0.13 microM). We also report the crystal structure of hPNMT in complex with sulfonamide 15, from which a potential hydrogen bond acceptor within the hPNMT active site has been identified, the main chain carbonyl oxygen of Asn39. The interaction of this residue with the sulfonamide -NH- is likely responsible for much of the enhanced inhibitory potency of the sulfonamides versus the sulfones.
Grunewald
Gary L
GL
Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045, USA. ggrunewald@ku.edu
Seim
Mitchell R
MR
Regier
Rachel C
RC
Martin
Jennifer L
JL
Gee
Christine L
CL
Drinkwater
Nyssa
N
Criscione
Kevin R
KR
D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D018360:Crystallography, X-Ray; D006801:Humans; D006860:Hydrogen Bonding; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D008297:Male; D008958:Models, Molecular; D015394:Molecular Structure; D010625:Phenylethanolamine N-Methyltransferase / Q000037:antagonists & inhibitors* / Q000737:chemistry; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D013450:Sulfones / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology
C514062:3-fluoromethyl-7-(3,3,3-trifluoropropylsulfonyl)-1,2,3,4-tetrahydroisoquinoline; D007546:Isoquinolines; D018341:Receptors, Adrenergic, alpha-2; D013449:Sulfonamides; D013450:Sulfones; D010625:Phenylethanolamine N-Methyltransferase