Michael A. Baldwin

Lipidic peptides. IV. Penicillin and cephalosporin amide conjugates with lipidic amino acids and their oligomers

Abstract A series lipidic amide conjugates ( 2b, c, 3b, c, 4b-d, 5b and c ) of β-lactam antibiotics were synthesised using mixed anhydride methods to couple the Boc-protected lipidic amino acids ( 1a and b ) and oligomer ( 1c ) to a variety of penicillins and cephalosporins. Conjugates ( 2b, c, 3b, 4b-d and 5b ) showed weak to moderate activity in vitro and were only weakly active in vivo against the non-β-lactamase producing stain S. aureus 663E .

An ingenane diterpene from belizian Mabea excelsa

The new ingenane diterpene, 5-deoxy-13-hydroxyingenol, was isolated from the alcohol preserved fresh latex of the stems of Mabea excelsa and characterized from its semi-synthetic triacetate. This is the first instance of an ingenane diterpene obtained from species other than those of Euphorbia and Elaeophorbia. This diterpene occurred in the latex in the form of an inseparable mixture of six aliphatic mono-esters of the tertiary C-13 hydroxy group.

Tautomerism in aromatic hydroxy N-heterocyclics in the gas phase by metastable ion mass spectrometry

The kinetic energy release associated with the decomposition of metastable ions has been used to differentiate between the hydroxyquinolines and hydroxypyridines and the corresponding tautomeric quinolinones and pyridinones in the gas phase. It is shown that 2-hydroxyquinoline exists in both tautomeric forms, whereas the other monohydroxyquinolines exist only in the hydroxy forms. The hydroxy forms are also favoured for the hydroxypyridines, but both the 3- and 4-isomers show some tendency to occur as the pyridinones, or, for the 3-isomer, the betaine.

Chlorine kinetic isotope effects. Application of the transition state model to thermolysis of secondary and tertiary alkyl chlorides

Chlorine kinetic isotope effects in the thermolysis of 2-chloropropane and 2-chloro-2-methyl-propane have been measured at temperatures between 250 and 441 °C. The isotope effects are primary and they show normal temperature dependence. They increase with increasing methyl substitution on the central carbon atom. Model calculations using the heavy atom approximation theory show satisfactory agreement with the experimental data and with the observed temperature dependence. The participation of chlorine in the activated complex is the same for primary, secondary and tertiary alkyl chlorides and involves a combination of C—Cl stretching (3 %), C—C—Cl bending (2.7 %) and C—CH3 shortening (4 %) from the ground state values.