The strategy exemplified here shows far-reaching possibilities for combinatorial engineering of polyketide natural products, as well as revealing the ability of modular polyketide synthases to 'skip' extension modules. The results also provide additional insight into the three-dimensional arrangement of modules within these giant synthases.

Glioblastoma remains an incurable brain cancer. Drugs developed in the past 20 years have not improved the prognosis for patients, necessitating the development of new treatments. We have previously reported the therapeutic potential of the quinoline methanol Vacquinol-1 (1) that targets glioblastoma cells and induces cell death by catastrophic vacuolization. Compound 1 is a mixture of four stereoisomers due to the two adjacent stereogenic centers in the molecule, complicating further development in the preclinical setting. This work describes the isolation and characterization of the individual isomers of 1 and shows that these display stereospecific pharmacokinetic and pharmacodynamic features. In addition, we present a stereoselective synthesis of the active isomers, providing a basis for further development of this compound series into a novel experimental therapeutic for glioblastoma.

Collision induced dissociation sequential mass spectrometry was used to investigate the fragmentation of the heptaketide macrolide aglycones, 6-deoxyerythronolide B (6-dEB), erythronolide B (EB), and acetate-starter EB (Ac-EB). The fragmentations of two previously reported octaketide analogs produced by "stuttering" of the erythromycin polyketide synthase, stuttered-6-dEB and acetate-starter stuttered-6-dEB were also studied. The accuracy with which the mass of each fragment was measured allowed it to be attributed to an unambiguous formula. Most of the experiments were repeated using samples dissolved in deuterated solvents. These data were then used to deduce plausible fragmentation pathways of the five compounds which were shown to have a high degree of similarity. Preliminary fragmentation analysis of a novel octaketide analog was performed and the structure was predicted as stuttered EB. Subsequent scale-up of the bacterial fermentations, followed by isolation and characterization by nuclear magnetic resonance spectroscopy confirmed this prediction. Further fragmentation experiments were then performed on this compound, which provided further evidence of the similarity of the fragmentation schemes. These results demonstrate the utility of collision induced dissociation sequential mass spectrometry analysis in the preliminary screening of bacterial fermentations for new polyketides. These studies were performed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. (J Am Soc Mass Spectrom 2002, 13, 862-874)