Highly stereocontrolled synthesis of a novel tribactam by reaction of an ester enolate with a N-trimethylsilylimine

My 50-Plus Years of Academic Research Collaborations with Industry. A Retrospective

A retrospective is presented highlighting the synthesis of selected "first-in-kind" natural products, their synthetic analogues, structure elucidations, and rationally designed bioactive synthetic compounds that were accomplished because of collaborations with past and present pharmaceutical and agrochemical companies. Medicinal chemistry projects involving structure-based design exploiting cocrystal structures of small molecules with biologically relevant enzymes, receptors, and bacterial ribosomes with synthetic small molecules leading to marketed products, clinical candidates, and novel drug prototypes were realized in collaboration. Personal reflections, historical insights, behind the scenes stories from various long-term projects are shared in this retrospective article.

Quantum mechanical calculations of the cephalosporin nucleus

A computational study using several ab initio methods, HF, DFT and MP2 at different basis set levels (6-31G*, 6-31G**, 6-311G** and 6-311++G**) has been performed to determine the possible stable conformations attained by the cephalosporin nucleus. The calculations were carried out in three stages by studying the conformational analysis of the 3-cephem nucleus, the 3-cephem-4-carboxylic acid nucleus and the acetylamino group of the 7-acetylamino-3cephem-4-carboxylic acid. In the first two stages, the potential energy surfaces indicated two minima that correspond to the S1-up and C2-up conformations, with the S1-up being more stable. The energy required for the interconversion of the S1-up to the C2-up is around 7 kcal/mol, indicating the feasibility of interconversion between the two conformers. In the third stage, the acetylamino group attained two conformations with respect to the 3-cephem nucleus. All the geometric parameters obtained in this study were found to be in reasonably good agreement with available X-ray diffraction data, even upon using a simple basis set.

Physico-chemical characterization of a novel tricyclic beta-lactam antibiotic

GV118819X, a novel tricyclic beta-lactam antibiotic of GlaxoWellcome, is a racemic mixture of two diastereoisomers, A and B. Of the two diastereoisomers, only A is available as a pure compound. By analyzing mixtures of GV118819X and A, a partial phase diagram is constructed, which indicates the presence of a eutectic when the A fraction is approximately 39%. Moreover, the melting enthalpies of the eutectic mixture and of diastereoisomer B can be estimated. With the exception of the pure A form, all mixtures undergo important modifications in morphology and microstructure as a consequence of thermal treatments, which induce melting/amorphization of the eutectic, and crystallization of the A form. Analyses of the sieved fractions of GV118819X demonstrate that it consists of acicular crystals of different composition, with the larger crystals having a larger A fraction than the smaller ones. Grinding causes melting/amorphization of the eutectic and, following hours-long treatments, the formation of a substantial fraction of submicron particles with unusually low melting temperatures.