Beetle Brood Balls Breed Polycyclic Puzzle

Tripartilactam: Confounding ChemDraw since 2012.

Natural product isolation chemists find fascinating molecules in wild, unexpected places. Hippo sweat. Deep-sea hydrothermal vents. Horse urine. Even maple syrup refining produces new compounds that chemists hope could be the next wonder drug. But a new paper from Org. Lett. ASAP brings forth a new discovery arena for me: dung beetles. Specifically, the giant balls of, well . . .poop, that they push around, then lay their eggs in.

Dung beetles with brood ball

Korean researchers have isolated tripartilactam from a Streptomyces species living in the beetles' brood ball, which they broke apart, cultured, and fractionated. Although the compound has no real biological activity, look at that structure: an 18-4-8 tricycle! Now, cyclobutanes are found in natural products all the time, from sceptrin to ladderanes, but usually not as a "bow-tie" bringing together two huge macrocycles. These scientists figure that a larger polyunsaturated structure was knit together by bacterial enzymes called polyketide synthases, followed by a light-initiated [2+2] to snap the cyclobutane shut.


Chemistry Note: Did you see that 18-4 trans ring juncture? Normally, that species would be far too strained to exist in anything below an 8-4 system. However, in a ring as large as 18, even with the rigid geometry enforced by the lactam and polyolefin chain, there's still enough wiggle room to accomodate this odd duck.