K. Jankowski

On the mechanism of the gif system for the oxidation of saturated hydrocarbons

Abstract The high selectivity of the Gif system for hydrocarbon oxidation is shown to depend upon the capture of tert. radicals by pyridine; the mechanism for the secondary oxidation products has only a minor radical component as judged by competitive trapping.

Approaches to the Total Synthesis of the Montanine (Amaryllidaceae) Alkaloids. Preparatiion of Isomeric 3-Aryloctahydroindoles

Etude de diverses methodes de synthese de [benzodiozole-1,3yl-5]-3 perhydro indolines isomeres

Mass spectral techniques in heterocyclic chemistry: applications and stereochemical considerations in carbohydrates and other oxygen heterocycles

Publisher Summary Mass spectrometry has evolved to one of the organic chemists most powerful tools for structure elucidation. The basic ionization form (electron impact, EI) involves the bombardment of gas-phase molecules by an electron beam which is energetic enough to ionize and induce a series of unimolecular fragmentations. Fast-atom bombardment (FAB) represents a totally novel and fresh approach to the concept of stereochemistry in mass spectrometry. The examples presented in this chapter reveals the influence of four independent parameters that govern a FAB spectrum in terms of whether or not ions can be observed and also whether structurally useful fragment ions can be produced. It can be predicted that FAB will become a valuable method for the sequencing of polysaccharides. This chapter illustrates that mass spectrometry has entered into the stereochemical studies field and has also emerged as an innovative research tool in biological and biochemical studies, an area where it has previously been confined to the rank of an analytical method. The chapter concludes that new techniques in sample preparation and introduction are also in the works (for example, ultrasound) to yield more reproducible (less time-dependent) spectra.

NMR investigations of proline and its derivatives: Part 5. A semi-empirical calculation of the endo-exo equilibrium of the pyrrolidine ring and its pH-dependence

Abstract Exo-endo interconversion of the pyrrolidine ring of l -proline is studied, using the correlation of vicinal interproton couplings to the molecular geometry parameters via the sum of direct carbon-proton couplings.

Gif oxidation of some alicyclic amines

Abstract The Gif oxidation of seven alicyclic tertiary amines leads essentially to the formation of lactams. The structure of the products present in trace amounts supports the mechanistic hypothesis previously advanced. The structures of the oxidation products were investigated using high performance GC-MS system.

On the gif oxidation of alicyclic tertiary amines

Abstract Oxidation of various tertiary amines by the Gif IV system based on an iron catalyst associated with a reductant (zinc) and molecular oxygen, led to a mixture of the ketoderivatives and the corresponding lactams. Steric hindrance and electron withdrawing substituents exert a deactivating effect on the oxidation.

2D 1H and 13C NMR in the conformation of 4-aryl derivatives of thieno[3,2-c]pyridines

Abstract In this paper we report the synthesis and spectral analysis of new heterocyclic derivatives of 4-aryl thieno[3,2-c]pyridines. These functionalized compounds were obtained from heteroaromatic aldehyde derivative and a cyclisation via tandem aza–Wittig iminophosphorane reactions sequence. The assignment of the structures and conformation of the different derivatives were achieved using 1D and 2D NMR (NOESY, DEPT, HMQC and HMBC).

Mass spectrometry of nucleic acids

Publisher Summary Nucleic acids are practically nonvolatile and usually possess a molecular weight of several million atomic mass units (amu) (μ) often expressed in daltons: up to 10 9 daltons where 1 dalton = 1.67 X 10 -24 g. They possess their own mass spectra. Generally, they are esters of phosphoric acid and polyols, such as the sugars ribose and 2′-deoxyribose, which are themselves substituted with heteroaromatic purine or pyrimidine bases. Consequently, fragment ions characteristic of all these structural elements can be found in the mass spectra of nucleic acids. The heterocyclic base moieties on the nucleic acids is important in the formation of hydrogen bonding and responsible for their essential functions, displaying a fairly predictable behavior under mass spectrometric conditions. Under normal electron impact (EI) conditions, these bases show a good stability related to a favored delocalization of the unpaired electrons. Because of this high stability of the species involved, ions due to base units are the most characteristic fragments obtained from the complex spectra of nucleic acids.

Functionalisation of saturated hydrocarbons. Part 3. The oxidation of 3β,5α,6β-triacetoxycholestane using the Gif system

The minor products from the oxidation of 3β,5α,6β-triacetoxycholestane using the Gif System [iron cluster–metallic zinc–pyridine–(aqueous) acetic acid–triplet oxygen] have been identified. The nature of the side-chain fragmentation to give 20-ketones has been clarified. Some mechanistic explanation has been offered for this unusual process.

Structure of Pt-DNA complexes in solution: Comparison of monodentate models

Abstract Possible mechanisms of the shrinkage of DNA after platination are considered. Atomic coordinates for the B/3-DNA complexes with Pt are calculated for the following three monodentate models: elastic; with opening of one GC pair; and with opening of a whole 3.4 nm segment of DNA (bubble-form type model). The last model turns out to be the only plausible one and compatible with the known facts concerning the behavior of the platinated DNA in solution.