Reactions of trimethylsilyl fluorosulfonyldifluoroacetate with purine and pyrimidine nucleosides

Difluorocarbene, generated from trimethylsilyl fluorosulfonyldifluoroacetate (TFDA), reacts with the uridine and adenosine substrates preferentially at the enolizable amide moiety of the uracil ring and the 6-amino group of the purine ring. 2′,3′-Di-O-benzoyl-3′-deoxy-3′-methyleneuridine reacts with TFDA to produce 4-O-difluoromethyl product derived from an insertion of difluorocarbene into the 4-hydroxyl group of the enolizable uracil ring. Reaction of the difluorocarbene with the adenosine substrates having the unprotected 6-amino group in the purine ring produced the 6-N-difluoromethyl derivative, while reaction with 6-N-benzoyl protected adenosine analogues gave the difluoromethyl ether product derived from the insertion of difluorocarbene into the enol form of the 6-benzamido group. Treatment of the 6-N-phthaloyl protected adenosine analogues with TFDA resulted in the unexpected one-pot conversion of the imidazole ring of the purine into the corresponding N-difluoromethylthiourea derivatives. Treatment of the suitably protected pyrimidine and purine nucleosides bearing an exomethylene group at carbons 2′, 3′ or 4′ of the sugar rings with TFDA afforded the corresponding spirodifluorocyclopropyl analogues but in low yields.     

Synthesis of novel indenoquinolines and indenopyridazines via photoisomerization of benzotropolone derivatives

We describe the photoisomerization of hetero Diels-Alder adducts of tetramethylpurpurogallin bearing β,γ-unsaturated ketone chromophores and endocyclic -N-O- or -N-N- groups. Based on spectroscopic and crystallographic data, our results indicate that the outcome of the reaction for the two types of substrates can be correlated with the difference in the stabilities of the radical intermediates generated in each case. For oxazines, the photoisomerization involves both the β,γ-unsaturated ketone and -N-O- moieties, and proceeds through the formation of allyl, benzoyl, phenyl, and α-carbonyl radical intermediates. While the same allylic and benzoyl radicals are formed in adducts with an -N-N- group, the hydrazine does not participate in the reaction and the product is a simple rearrangement of the initial intermediate.     

Enantiospecific wetting

Experiments have shown that enantiospecificity can be important in wetting. Measurements of droplet contact angles can be used to estimate the energy of enantiomeric discrimination.     

Ruthenium-caged antisense morpholinos for regulating gene expression in zebrafish embryos

Photochemical approaches afford high spatiotemporal control over molecular structure and function, for broad applications in materials and biological science. Here, we present the first example of a visible light responsive ruthenium-based photolinker, Ru(bipyridine)₂(3-ethynylpyridine)₂ (RuBEP), which was reacted stoichiometrically with a 25mer DNA or morpholino (MO) oligonucleotide functionalized with 3′ and 5′ terminal azides, via Cu(i)-mediated [3+2] Huisgen cycloaddition reactions. RuBEP-caged circular morpholinos (Ru-MOs) targeting two early developmental zebrafish genes, chordin and notail, were synthesized and tested in vivo. One-cell-stage zebrafish embryos microinjected with Ru-MO and incubated in the dark for 24 h developed normally, consistent with caging, whereas irradiation at 450 nm dissociated one 3-ethynylpyridine ligand (Φ = 0.33) and uncaged the MO to achieve gene knockdown. As demonstrated, Ru photolinkers provide a versatile method for controlling structure and function of biopolymers.     

Protonierte fluorenon-ionen aus N.N-diarylsubstituierten 1.4-diazaspiro[4.4]nonanen: Eine neue elektronenstossinduzierte arylwanderung

Using collisional activation mass spectrometry (CA) and suitable reference ions it can be shown that the title compounds rearrange to protonated fluorene ions. The mechanism of this novel aryl migration as well as possible alternative ion structures are discussed.