Chemistry of Diazabicycloundecene (DBU) and Other Pyrimidoazepines

A Greener Technique for Microwave-Assisted O-Silylation and Silyl Ether Deprotection of Uridine and Other Substrates

A single clean, good-yielding, environment-friendly microwave-assisted procedure for O-silylation of uridine with tert-butyldimethylsilyl chloride (TBDMSCl), 1,8-Diazabicyclo(5.4.0)undec-7-ene (DBU) and potassium nitrate as catalyst under solvent-free conditions is reported. Subsequent silyl ether deprotection is accomplished with a reusable acidic resin via microwave irradiation. Both the silylation and desilylation protocols have been applied to a panel of alcohols of pharmaceutical interest.

Structural features of selected protic ionic liquids based on a super-strong base

Protic ionic liquids (PIL) were prepared from a super-strong base 1,7-diazabicyclo[5.4.0]undec-7-ene (DBU) and super-strong acids, trifluoromethane sulfonic acid (TfOH), and (trifluoromethanesulfonyl)-(nonafluorobutylsulfonyl)imide, (IM14H), ([DBUH][TfO] and [DBUH][IM14], respectively; the latter for the first time) and their chemical and physical properties and structural features have been explored using a synergy of experimental and computational tools. The short range order in neat DBU, as well as the long range structural correlations induced by charge correlation and hydrogen bonding interactions in the ionic liquids, have been explored under ambient conditions, where these compounds are proposed for a variety of applications. Similar to other [DBUH]-based PILs, the probed ones behave as good ionic liquids. Molecular dynamics-rationalised X-ray diffraction patterns show the major role played by hydrogen bonding in affecting morphology in these systems. Additionally, we find further evidence for the existence of fluorous domains in [DBUH][IM14], thus potentially extending the range of applications for these PILs.

Molecular recognition studies of selected isoalloxazines with 2,6-diamidopyridine derivatives

Triple hydrogen bond formation towards the uracil moiety of an isoalloxazine ring with 2,6-diamidopyridine derivatives has been observed in chloroform. A hydrogen bonded isoalloxazine–pyridine complex has been successfully utilised in disulfide formation as a metal-free organocatalyst.

Key factor governing the physicochemical properties and extent of proton transfer in protic ionic liquids: ΔpKa or chemical structure?

A series of protic ionic liquids (PILs) are prepared by neutralisation of bis(trifluoromethanesulfonyl)amide acid (H[NTf₂]) with various amines, and the properties (especially thermal stability and ionicity) are compared with those of PILs from 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) and various acids.

Studies toward the synthesis of cinachyramine. An efficient route to 1,5-diazabicyclo[4.4.0]dec-5-enes

Hydrogenation (3 atm) of readily available pyrido[1,2-a]pyrimidines 10, 14, and 17 over 5% Rh/Al₂O₃ forms 1,5-diazabicyclo[4.4.0]dec-5-enes 9, 15, and 18 in > 95% yield, providing a general route to this little-studied class of compounds. All attempts to form the tetrahydro-1,2,4-triazine moiety of cinachyramine (1) by rearrangement of amidinium dimethylhydrazone 8 using the procedures developed by Kamatori to convert hydrazone 3a to tetrahydro-1,2,4-triazine 4a were unsuccessful.

Pentacyclic coumarin-based blue emitters – the case of bifunctional nucleophilic behavior of amidines

Esters of coumarin-3-carboxylic acids undergo addition to DBU and DBN leading to the formation of a 6-membered ring.

[11C]GR103545: novel one-pot radiosynthesis with high specific activity

INTRODUCTION

GR103545 is a potent and selective kappa-opioid receptor agonist. Previous studies in non-human primates demonstrated favorable properties of [(11)C]GR103545 as a positron emission tomography tracer for in vivo imaging of cerebral kappa-opioid receptor. Nonetheless, advancement of [(11)C]GR103545 to imaging studies in humans was hampered by difficulties of its multiple-step radiosynthesis, which produces a final product with low specific activity (SA), which in turn could induce undesirable physiological side effects resulting from the mass associated with an injected amount of radioactivity. We report herein an alternative radiosynthesis of [(11)C]GR103545 with higher SA and radiochemical yields.

METHODS

The TRACERLab FXC automated synthesis module was used to carry out the two-step, one-pot procedure. In the first step, the desmethoxycarbonyl precursor was converted to the carbamic acid intermediate desmethyl-GR103545 via transcarboxylation with the zwitterionic carbamic complex, 1,8-diazabicyclo[5.4.0]undec-7-ene-carbon dioxide, in the presence and/or absence of cesium carbonate and tetrabutylammonium triflate. In the second step, the intermediate was radiolabeled at the carboxyl oxygen with [(11)C]methyl trifluoromethanesulfonate to give [(11)C]GR103545.

RESULTS

This novel synthesis produced [(11)C]GR103545 with ≥90% chemical and radiochemical purities and an SA of 290.45±99.9 MBq/nmol at the end of synthesis (n=26). Injectable radioactivity was 1961±814 GBq/μmol with 43 min of average synthesis time from the end of beam.

CONCLUSION

We have developed a practical one-pot method for the routine production of [(11)C]GR103545 with reliably high SA and radiochemical yield, thus allowing the advancement of this radiotracer to imaging applications in humans.

Trapping of Hemiquinone Radicals at Mo and P Sites by Phosphide-Bridged Dimolybdenum Species: Chemistry of Complexes [Mo2(η5-C5H5)2(OC6H4OH)(μ-PR2)(CO)4] and [Mo2(η5-C5H5)2{μ-PR(OC6H4OH)}(CO)4]- (R = Cy, Ph)

The phosphide-bridged dimolybdenum complexes (H-DBU)[Mo2Cp2(mu-PR2)(CO)4] (R= Cy, Ph; DBU = 1,8-diazabicyclo[5.4.0.]undec-7-ene) react with p-benzoquinone to give the hemiquinone complexes [Mo(2)Cp2(OC6H4OH)(mu-PR2)(CO)4]. The latter experience facile homolytic cleavage of the corresponding Mo-O bonds and react readily at room temperature with HSPh or S2Ph2 to give the thiolate complexes [Mo2Cp2(mu-PCy2)(mu-SPh)(CO)4] or [Mo2Cp2(mu-PR2)(mu-SPh)(CO)2]. In contrast, PRH-bridged substrates experience overall insertion of quinone into the P-H bond to give the anionic compounds (H-DBU)[Mo(2)Cp2{mu-PR(OC6H4OH)}(CO)4], which upon acidification yield the corresponding neutral hydrides. The cyclohexyl anion experiences rapid nucleophilic displacement of the hemiquinone group by different anions ER- (ER = OH, OMe, OC4H5, OPh, SPh) to give novel anionic compounds (H-DBU)[Mo2Cp2{mu-PCy(ER)}(CO)4], which upon acidification yield the corresponding neutral hydrides. The structure of four of these hydride complexes [PPh(OC6H4OH), PCy(OH), PCy(OMe), and PCy(OPh) bridges] was determined by X-ray diffraction methods and confirmed the presence of cis and trans isomers in several of these complexes. In addition, it was found that the hydroxyphosphide anion [Mo2Cp2{mu-PCy(OH)}(CO)4]- displays in solution an unprecedented tautomeric equilibrium with its hydride-oxophosphinidene isomer [Mo2Cp2(mu-H){mu-PCy(O)}(CO)4]-.

Structural, CV and IR spectroscopic evidences for preorientation in PET-active phthalimido carboxylic acids

Hydrogen bond and potassium cation mediated preorientation were detected for phthalimido acetic acid and the corresponding acetate. Evidence for these phenomena came from X-ray structure analysis as well as cyclic voltammetric and IR spectroscopic measurements. These interactions rationalize the photoinduced electron transfer (PET) reactivity of the substrates in photodecarboxylation reactions.