Iterative Mechanism of Macrodiolide Formation in the Anticancer Compound Conglobatin

Abstract

SummaryConglobatin is an unusual C2-symmetrical macrodiolide from the bacterium Streptomyces conglobatus with promising antitumor activity. Insights into the genes and enzymes that govern both the assembly-line production of the conglobatin polyketide and its dimerization are essential to allow rational alterations to be made to the conglobatin structure. We have used a rapid, direct in vitro cloning method to obtain the entire cluster on a 41-kbp fragment, encoding a modular polyketide synthase assembly line. The cloned cluster directs conglobatin biosynthesis in a heterologous host strain. Using a model substrate to mimic the conglobatin monomer, we also show that the conglobatin cyclase/thioesterase acts iteratively, ligating two monomers head-to-tail then re-binding the dimer product and cyclizing it. Incubation of two different monomers with the cyclase produces hybrid dimers and trimers, providing the first evidence that conglobatin analogs may in future become accessible through engineering of the polyketide synthase.

The Biosynthesis of the Benzoxazole in Nataxazole Proceeds via an Unstable Ester and has Synthetic Utility

“…Oxazoles in both families derive from nucleophilic attack of the hydroxyl group of Ser(Thr) upon amide bonds through a common hemiorthoamide intermediate (Figure b), but via distinct enzymatic routes . Two polyketide synthase–NRPS hybrid natural products, oxazolomycin and conglobatin, have been proposed to utilize an N‐type ATP pyrophosphohydrolase to form oxazoles . None of these enzymes have been reported to catalyze the formation of benzoxazole and such activity would seem unlikely based on their known substrates.…”

“…[23][24][25][26][27][28][29][30][31][32][33][34] Tw o polyketide synthase-NRPS hybrid natural products,o xazolomycin and conglobatin, have been proposed to utilize an Ntype ATPpyrophosphohydrolase to form oxazoles. [35,36] None of these enzymes have been reported to catalyze the formation of benzoxazole and such activity would seem unlikely based on their known substrates.…”

Evidence for an iterative module in chain elongation on the azalomycin polyketide synthase

“…Such skipping of a single, apparently active domain in a cis -AT PKS is well-precedented [45–47]. The bioinformatic prediction of the configuration at each of the seven asymmetric centres was also in accord with the configuration of authentic ebelactone confirmed by total synthesis [48] (Scheme 1).…”

Enantioselective Rhodium‐Catalyzed Dimerization of ω‐Allenyl Carboxylic Acids: Straightforward Synthesis of C2‐Symmetric Macrodiolides

“…[1,2] Aside from unsymmetrical heterogeneous dimers,agroup of complex C 2symmetrical oxacyclic diolides comprise al arge number of biologically active compounds (Scheme 1). [1,2] Aside from unsymmetrical heterogeneous dimers,agroup of complex C 2symmetrical oxacyclic diolides comprise al arge number of biologically active compounds (Scheme 1).…”

“…Inrecent decades,d imeric structures of polyketide origin have gained increasing scientific attention, since they show ar ange of unique structural features and great potential as novel medicinally relevant substances. [1,2] Aside from unsymmetrical heterogeneous dimers,agroup of complex C 2symmetrical oxacyclic diolides comprise al arge number of biologically active compounds (Scheme 1). In this group, immunosuppressives, [3a-c] antibiotics, [3d-f] anthelmintics, [3g,h] herbicides,a nd fungicides, [3i,j] as well as active agents against cancer, [3k-m] HIV,a nd the tropical disease malaria can be found.…”