The unorthodox loss of propyl from the molecular ions of methoxycyclohexane

It is shown by field ionization kinetics, D and ¹³C labelling and metastable ion studies that the loss of a propyl radical from the molecular ion of methoxycyclohexane occurs via two routes. At a molecular ion lifetime of <10^?10 s propyl is eliminated in the ‘classic’ way, i.e. by successive cleavage of the C(1)? C(2) bond, 1,5-H shift from C(6) to C(2) and cleavage of the C(4)? C(5) bond. At 10^?10 s the other pathway for propyl loss starts to take place, which is initiated by a hydrogen shift from position 3 or 5 to the methoxy group. This leads in a series of steps to the formation of the 3-methoxyhexene-1 ion, which eventually eliminates a propyl radical. In some of the steps specific hydrogen-deuterium exchange processes have been observed.     

Synthesis and SAM formation of water soluble functional carboxymethylcelluloses: thiosulfates and thioethers

Functional thiomethyl and thiosulfate derivatives of carboxymethylcellulose (CMC, DS = 0.9) were synthesized by nucleophilic displacement reactions. Alkylation of CMC by allyl glycidyl ether took mainly place at the primary positions of the cellulose backbone and yielded a 6-O-(3-allyloxy-2-hydroxypropyl)-CMC 1 with a partial DS of 3-allyloxy-2-hydroxypropyl substituents DSallyl of up to 0.43. Addition of tetrathionate to the allyl groups gave rise to 6-O-(2,3-bis(thiosulfato)propoxy-2-hydroxypropyl)-CMC 2. As the addition of tetrathionate was sluggish and incomplete, alternatively bromine was added and the resulting dibromide was substituted by thiosulfate. A 40% conversion of the allyl groups was achieved by this two-step procedure. On the other hand, the addition of bromine to 1 in aqueous solution almost quantitatively yielded the bromohydrin derivative which was converted by displacement reaction with thiosulfate to 6-O-(2-hydroxy-3-thiosulfatopropoxy-2-hydroxypropyl)-CMC 4. 6-Thiomethyl-6-deoxy-CMC 6 was synthesized by displacement reaction of 6-O-tosylcellulose with sodium methylsulfide and subsequent carboxymethylation of the cellulose backbone. A partial DS of thiomethyl substituents DSThM=0.65 exclusively at the primary positions was obtained. All functional CMC derivatives, 2, 4, and 6 were readily available in gram quantities, rather stable and highly water soluble for pH > 3. On gold surfaces they form self-assembled monolayers (SAMs) with thicknesses of 1.2 to 2.4 nm as determined by surface plasmon resonance (SPR).     

A versatile approach towards regioselective platinated DNA sequences

Undesired N(7) platination of 2'-deoxyguanosine residues at predetermined sites in an oligodeoxynucleotide (ODN) sequence is prevented by applying the sterically demanding diphenylcarbamoyl (DPC) as an O(6)-protecting group. The presence of a base-labile oxalyl linker between the immobilized 3'-nucleotide and controlled pore glass (CPG) allows cleavage of the protected ODN from the support and leaves DPC protection unaffected. This method provides an ODN with specifically blocked guanine-N(7) sites for platination. In the hexanucleotides prepared in this study, 5'-GGBGGT-3'(for B=T, C and A), a platinum GG adduct is introduced at G4,G5. These site-specific platinated hexamers were isolated in a yield of 65 %, and were fully characterized by using reversed-phase HPLC (high performance liquid chromotography), LCMS (liquid chromatography-mass spectrometry), MALDI-TOF MS (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry), PAGE (polyacrylamide gel electrophoresis) and Maxam-Gilbert sequencing analysis.     

On the mechanism of the ethyl elimination from the molecular ion of 6-methoxy-1-hexene

It is shown by ¹³C and D labelling that the ethyl radical elimination from the molecular ion of 6-methoxy-1-hexene is a very complex process involving at least two different channels. The major channel (80%) is induced by an initial 1,5-hydrogen shift in the molecular ion from C(5) to C(l) leading via a series of steps to methoxy-cyclohexnne, which then undergoes a ring contraction to 2-methyl-1-methoxycyclopentane, being the key intermediate for the ethyl loss. The same key intermediate is formed in the other, minor channel (20%) by ring closure directly following an initial 1,6-hydrogen shift in the molecular ion of 6-methoxy-1-hexene from C(6) to C(l). Collision-induced dissociation experiments on the [M ? ethyl]⁺ ion from 6-methoxy-1-hexene have further established that it has the unique structure of oxygen methyl cationized 2-methyIpropen-2-al. This ion is also generated by ethyl loss from the molecular ion of 2-methyl-1-methoxycyclopentane itself, as shown by collision-induced dissociation experiments, thus confirming the key role of the intermediate mentioned.     

Mechanistic studies on the formation of Pt(II) hydroformylation catalysts in imidazolium-based ionic liquids

The kinetics of the formation of the active species cis-[Pt^II(PPh₃)₂Cl(SnCl₃)] and cis-[Pt^II(PPh₃)₂(SnCl₃)₂] from the hydroformylation catalyst precursor cis-[Pt^II(PPh₃)₂Cl₂] in the presence of SnCl₂, was studied in two different imidazolium-based ionic liquids. A large range of different chlorostannate melts consisting of 1-butyl-3-methyl-imidazolium cations and [Sn_xCl_y]^{(−y + 2x)} anions with varying molar fraction of SnCl₂, were prepared and characterized by ¹H and ¹¹⁹Sn NMR. The observed chemical shifts point to major changes in the composition of the anionic species within the melt. The second ionic liquid employed, viz., 1-butyl-3-methyl-imidazolium-bis(trifluormethylsulfonyl)amide was prepared in a colorless quality that enabled its application in kinetic studies. The concentration and temperature dependence of the substitution of Cl⁻ by [SnCl₃]⁻ to yield cis-[Pt^II(PPh₃)₂Cl(SnCl₃)], could be studied in detail. Theoretical (DFT) calculations were employed to model the reaction progress and to resolve the role of the ionic liquid in the activation of the catalyst. The available results are presented and a plausible mechanism for the formation of the catalytically active species is suggested.     

Nucleoside und Nucleotide. Teil 10. Synthese von Thymidylyl-(3′-5′) -thymidylyl-(3′-5′)-1-(2′-desoxy-β-D-ribofuranosyl)-2(1 H)-pyridon

Nucleosides and Nucleotides. Part 10. Synthesis of Thymidylyl-(3′-5′)-thymidylyl-(3′-5′)-1-(2′-deoxy-β-D - ribofuranosyl)-2(1 H)-pyridone The synthesis of 5′-O-monomethoxytritylthymidylyl-(3′-5′)-thymidylyl-(3′-5′)-1-(2′-deoxy-β-D -ribofuranosyl)-2(1H)-pyridone ((MeOTr)T_dpT_dp∏_d, 5 ) and of thymidylyl-(3′-5′)-thymidylyl-(3′-5′)-1-(2′-deoxy-β-D -ribofuranosyl)-2(1 H)-pyridone (T_dpT_dp∏_d, 11 ) by condensing (MeOTr) T_dpT_d ( 3 ) and p∏_d(Ac) ( 4 ) in the presence of DCC in abs. pyridine is described. Condensation of (MeOTr) T_dpT_dp ( 6 ) with Π_d(Ac) ( 7 ) did not yield the desired product 5 because compound 6 formed the 3′-pyrophosphate. The removal of the acetyl- and p-methoxytrityl protecting group was effected by treatment with conc. ammonia solution at room temperature, and acetic acid/pyridine 7 : 3 at 100°, respectively. Enzymatic degradation of the trinucleoside diphosphate 11 with phosphodiesterase I and II yielded T_d, pT_d and p∏_d, T_dp and Π_d, respectively, in correct ratios.