Crosstalk between primary and secondary metabolism: Interconnected fatty acid and polyketide biosynthesis in prokaryotes.

In primary metabolism, fatty acid synthases (FASs) biosynthesize fatty acids via sequential Claisen-like condensations of malonyl-CoA followed by reductive processing. Likewise, polyketide synthases (PKSs) share biosynthetic logic with FAS which includes utilizing the same precursors and cofactors. However, PKS biosynthesize structurally diverse, complex secondary metabolites, many of which are pharmaceutically relevant. This digest covers examples of interconnected biosynthesis between primary and secondary metabolism in fatty acid and polyketide metabolism. Taken together, further understanding the biosynthetic linkage between polyketide biosynthesis and fatty acid biosynthesis may lead to improved discovery and production of novel drug leads from polyketide metabolites.

Synthesis, photophysical and nonlinear optical properties of push-pull tetrazoles.

A 2,5-disubstituted tetrazole with p-nitrophenyl and 3-pyridyl units as acceptors (1a), and three push-pull tetrazoles with p-nitrophenyl as an acceptor and phenyl (1b), 2-(dibenzo[b,d]furan-4-yl) (1c), and 4-(N,N-diphenylamino)phenyl (1d) as donor groups, were synthesized by copper-catalyzed aerobic C-N coupling of p-nitrophenyl tetrazole with appropriately substituted aryl boronic acids. The absorption and emission spectra of 1a-c showed minimal dependence on the polarity of the solvent; however, in the case of 1d a blue shift was noted in the longest absorption band (λ 1) as the polarity increased. The fluorescence intensity of the title compounds was found to be solvent-dependent; however, no apparent correlation to solvent polarity could be established. The absorption and emission characteristics of 1a-d were also influenced by the nature of the substituent as 1d, bearing a strong electron donating 4-(N,N-diphenylamino)phenyl group, displayed a significant red shifted absorption (λ 1) as well as emission (λ em) bands compared to other compounds. Time dependent density functional calculations (CAM-B3LYP/6-311++G**) revealed that the longest wavelength band (λ 1) is associated with an intramolecular charge transfer (ICT) from HOMO/HOMO-1/HOMO-2 → LUMO/LUMO+1 in these molecules. The first hyperpolarizability values, ß HRS, of 1a-d were measured using the solution-based hyper-Rayleigh scattering technique using a femtosecond Ti:Sapphire laser and the highest NLO activity was measured for 1d with the greatest push-pull characteristics. A strong correlation was observed between the calculated hyperpolarizability (ß tot) and experimentally measured values (ß HRS).