No abstract

No abstract

No abstract

No abstract

The tubulysins are a family of complex peptides with promising cytotoxic activity against multi-drug-resistant tumors. To date, ten tubulysins have been described from the myxobacterial strains Angiococcus disciformis An d48 and Archangium gephyra Ar 315. We report here a third producing strain, Cystobacter sp. SBCb004. Comparison of the tubulysin biosynthetic gene clusters in SBCb004 and An d48 reveals a conserved architecture, allowing the assignment of cluster boundaries. A SBCb004 strain containing a mutant in the putative cyclodeaminase gene tubZ accumulates pretubulysin A, the proposed first enzyme-free intermediate in the pathway, whose structure we confirm by NMR. We further show, using a combination of feeding studies and structure elucidation by NMR and high-resolution tandem mass spectrometry, that SBCb004 and An d48 together biosynthesize 22 additional tubulysin derivatives. These data reveal the inherently diversity-oriented nature of the tubulysin biosynthetic pathway.

Keywords:Total synthesis / Antitumor agents / Myxobacteria / Natural products / Tubulysins / Pretubulysin Pretubulysin, a biosynthetic precursor of the tubulysins, shows potent biological activity in the subnanomolar range towards various tumor cell lines. Its activity is only slightly less than those of the structurally more complex tubulysins. With a straightforward synthesis to hand, pretubulysin is an

Simplify, simplify, simplify! Pretubulysin (structure without the green substituents), a simplified tubulysin was prepared in the laboratory and also found in a natural myxobacterial source. This biosynthetic precursor of the tubulysins is not as active as tubulysins A and D but is still effective in picomolar concentrations against cancer cell lines.

A new cyclic octapeptide, cyclo(Ile-Ser-(Gly)Thz-Ile-Thr-(Gly)Thz) (PatN), related to patellamide A, has been synthesized and reacted with copper(II) and base to form mono- and dinuclear complexes. The coordination environments around copper(II) have been characterized by EPR spectroscopy. The solution structure of the thermodynamically most stable product, a purple dicopper(II) compound, has been examined by simulating weakly dipole-dipole coupled EPR spectra based upon structural parameters obtained from force field (MM and MD) calculations. The MM-EPR method produces a saddle-shaped structure for [Cu(2)(PatN)(OH(2))(6)] that is similar to the known solution structure of patellamide A and the known solid-state structure of [Cu(2)(AscidH(2))CO(3)(OH(2))(2)]. Compared with the latter, [Cu(2)(PatN)] has no carbonate bridge and a significantly flatter topology. The MM-EPR approach to solution-structure determination for paramagnetic metallopeptides may find wide applications to other metallopeptides and metalloproteins.