4-Chlorobenzyl sulfonamide and sulfamide derivatives of histamine homologues: the design of potent histamine H3 receptor antagonists

Synthetic methodology for the preparation of N-hydroxysulfamides

A convenient synthesis of a variety of substituted N-hydroxysulfamides from chlorosulfonyl isocyanate is reported. Alkyl groups can be introduced selectively on the N-Boc nitrogen of key intermediates 1a or 1b using the Mitsunobu reaction with alcohols. Subsequently the nitrogen carrying the silyloxy group can be alkylated under traditional conditions. Deprotection to the desired N-hydroxysulfamide can be achieved in high yields. Using this method, a number of structurally diverse N-hydroxysulfamides have been prepared. The usefulness of this methodology has further been demonstrated by the synthesis of more complex targets such as bis-hydroxysulfamide, 5, and cyclic hydroxysulfamides 7 and 8.

Bromoallenes as Allyl Dication Equivalents in the Presence or Absence of Palladium(0): Direct Construction of Bicyclic Sulfamides Containing Five- to Eight-membered Rings by Tandem Cyclization of Bromoallenes

A highly regioselective synthesis of bicyclic sulfamides is described. Based on our recent discovery that bromoallenes can act as allyl dication equivalents in the presence of a palladium catalyst and alcohol, we investigated tandem cyclization of bromoallenes bearing a sulfamide group. It is found that some bromoallenes act as allyl dication equivalents even in the absence of a palladium(0) catalyst to afford cyclosulfamides containing five- or six-membered rings. While the palladium-free cyclization is dependent on the substrate structure affording the bicyclic sulfamides through the first cyclization onto the proximal or central carbon atom of the bromoallenes, the palladium-catalyzed reaction strongly promotes the first cyclization onto the central allenic carbon atom to afford bicyclic sulfamides containing a seven- or eight-membered ring. Formation of two types of bicyclic sulfamides from single bromoallenes by simply changing the reaction conditions is also described.

An investigation of the absolute configuration of the potent histamine H3 receptor antagonist GT-2331 using vibrational circular dichroism

GT-2331 [(+)-1] is one of the most potent members of a class of chiral drug substances used to regulate the synthesis and release of histamine by the histamine H3 receptor, and as such, is an important biomarker for pharmaceutical companies conducting research in this field. In addition to overall structural features, the bioactivity of this molecule has also been found to be highly dependent on absolute stereochemistry, making the reliable assignment of this property a necessity. X-ray diffraction studies have provided conflicting data, leaving its three-dimensional structure uncertain. In view of this, its absolute configuration was investigated by vibrational circular dichroism. Results from this study provided independent assignment of this important molecule as the (1S,2S)-enantiomer.

New uses for the Burgess reagent in chemical synthesis: methods for the facile and stereoselective formation of sulfamidates, glycosylamines, and sulfamides

Although the Burgess reagent (methoxycarbonylsulfamoyltriethylammonium hydroxide, inner salt) has found significant use in chemical synthesis as a dehydrating agent, almost no work has been directed towards its potential in other synthetic applications. As this article will detail, we have found that the Burgess reagent is remarkably effective at accomplishing a number of non-dehydrative synthetic tasks when applied to appropriate substrates, such as the formation of sulfamidates from 1,2-diols or epoxyalcohols, alpha- and beta-glycosylamines from carbohydrates, and cyclic sulfamides from 1,2-aminoalcohols. Beyond delineating the power of these new reaction manifolds, we also describe the construction of a group of alternative Burgess-type reagents that extends the scope of these new reactions even further.

The role of HB-donor groups in the heterocyclic polar fragment of H3-antagonists

It has been recently reported that compounds composed of an imidazole connected through an alkyl spacer to a 2-aminobenzimidazole showed high affinity towards the H(3)-receptor. The guanidine fragment of the 2-aminobenzimidazole is probably involved in hydrogen bond interactions at the binding site, and is referred to as the 'polar fragment'. In the present work, starting from 2-aminobenzimidazole derivatives with a di-methylene spacer 1 (pK(i)=7.25) or a tri-methylene one 2 (pK(i)=8.90), we investigated the importance of the hydrogen bond (HB) donor groups at the polar fragment in the interaction with the H(3)-receptor. The replacement of 2-aminobenzimidazoles with different moieties [2-aminobenzothiazole, 3, 4; 2-thiobenzimidazole, 5, 6; 2-thiobenzothiazole, 7, 8; 2-thio-4-phenyl- or 2-thio-5-phenyl-N-methylimidazoles, 9-12] highlighted the effect of the polar group basicity on the optimal length of the alkyl chain: longer spacers were preferred with polar groups of moderate basicity whereas, in the presence of neutral polar groups, the best affinity values were obtained with di-methylene chains. Moreover, N-methylation at the 2-aminobenzimidazole moiety 13-16 revealed different behaviour for compounds having different spacer lengths. In fact, methylation of the exocyclic NH group maintained high affinity for the tri-methylene 2-aminobenzimidazole derivative, while a drop in affinity was observed for the annular N-methylation. An opposite trend characterised di-methylene derivatives. These observed SAR suggest that, within this class of compounds, the number of HB-donor groups can be lowered while maintaining high receptor affinity. Since the presence of HB-donor groups strongly affects brain access, this observation could be useful to design and prepare new H(3)-antagonists.

omega-(Imidazol-4-yl)alkane-1-sulfonamides: a new series of potent histamine H(3) receptor antagonists

omega-(1H-Imidazol-4-yl)alkane-1-sulfonamides were prepared and found to be potent histamine H(3) receptor antagonists. High receptor affinity and a low difference in the data between the bioassays were achieved with 5-(1H-imidazol-4-yl)pentane-1-sulfonic acid 4-chlorobenzylamide (16). Good in vitro profiles were also obtained for 2-hydroxysulfonamide and vinylsulfonamide analogues. This complements and completes the existing set of imidazole-based sulfonamides and sulfamides.

Synthesis of cyclic sulfonamides through intramolecular Diels-Alder reactions

[figure: see text] Substituted 2,3,3a,4,5,7a-hexahydrobenzo[d]isothiazole 1,1-dioxides and 3,4,4a,5,6,8a-hexahydro-2H-benzo[e][1,2]thiazine 1,1-dioxides, novel cyclic sulfonamides, were synthesized by the thermal Diels-Alder reaction of triene derivatives of buta-1,3-diene-1-sulfonic acid amide. The stereochemical outcome of the reaction was determined by NMR spectroscopy and X-ray crystallographic analysis. This chemistry has been used for the synthesis of 2-(4-chlorobenzyl)-5-(1H-imidazol-4-yl)-2,3,3a,4,5,7a-hexahydrobenzo[d] isothiazole 1,1-dioxide, a histamine H3 receptor antagonist.