Cyanophosphates (CPs) can be easily prepared from either ketones or aldehydes, and their reaction with NaN3–Et3N·HCl results in the formation of azidotetrazoles. Under microwave irradiation, successive fragmentation of the azidotetrazoles generates alkylidene carbenes that undergo [1,2]-rearrangement and are transformed into homologous alkynes. Treatment of ketone-derived CPs with TMSN3 and Bu2SnO as catalyst in toluene at reflux directly yields the corresponding internal alkynes, whereas the reaction of aldehyde-derived CPs with NaN3–Et3N·HCl in THF at reflux or TMSN3–Bu2SnO (cat.) in toluene at reflux provides homologous terminal alkynes in good yields. These reactions take place under neutral conditions and can be successfully extended to obtain alkynes that are not usually accessible from the corresponding carbonyl compounds by the Ohira–Bestmann or Shioiri procedures, which require basic conditions.

Cyanophosphates (CPs) can easily be prepared via the reactions of carbonyl compounds with diethyl phosphorocyanidate (DEPC) in the presence of LiCN (cat.) under non-aqueous conditions. Treatment of ketone-derived CPs with TMSN3/Bu2SnO (cat.) in toluene at reflux produces cyclopentenes or heterocyclic products in good yields under neutral conditions. In this two-step transformation, CPs may form tetrazolylphosphates, which subsequently undergo successive fragmentation to generate alkylidene carbenes, which undergo [1,5]-C–H insertions to yield five membered compounds.Download high-res image (134KB)Download full-size image

S-Alkyl-N-alkylisothiourea compounds containing various cyclic amines were synthesized in the search for novel nonimidazole histamine H3 receptor (H3R) antagonists. Among them, four N-alkyl S-[3-(piperidin-1-yl)propyl]isothioureas 18, 19, 22, and 23 were found to exhibit potent and selective H3R antagonistic activities against in vitro human H3R, but were inactive against in vitro human H4R. Furthermore, three alkyl homologs 18–20 showed inactivity for histamine release in in vivo rat brain microdialysis, suggesting differences in antagonist affinities between species. In addition, in silico docking studies of N-[4-(4-chlorophenyl)butyl]-S-[3-piperidin-1-yl)propyl]isothiourea 19 and a shorter homolog 17 with human/rat H3Rs revealed that structural differences between the antagonist-docking cavities of rat and human H3Rs were likely caused by the Ala122/Val122 mutation.OUP-186: histamine H3R antagonist inactive in rats, but especially potent in humans.Figure optionsDownload full-size imageDownload as PowerPoint slide

Novel C5-linked C0- and C2-tetrazole ribonucleoside phosphoramidites were designed and synthesized via tetrazole C-nucleosides. Pivaloyloxymethyl (POM) and methyl-substituted POM (MePOM) groups were introduced as N-protecting groups in the tetrazole ring that can be readily removed under mild basic conditions. The phosphoramidites were successfully incorporated into the VS ribozyme substrate and hence providing a chemogenetic approach to determine which nucleobases of ribozymes function as the acid or base, in the studies of ribozyme general acid and base catalysis.