[Melchizedek]

I'm trying to find examples of naturally occuring sulphonamides. So far I haven't found any. Do they exist or do they have to be manmade?

What would the rationale be for this?

[shelanachium]

Sulfonic acids, from which sulfonamides would presumably be biosynthesised, are themselves quite unusual in natural products. One which is common is taurine, 2-aminoethanesulfonic acid H2NCH2CH2SO3H. I have not heard of its amide being found in Nature.

To find unusual structures in biological molecules, search databases of fungal and bacterial products. You will find some weird structures indeed. Plants don't do badly either. They probably stole the genes responsible from bacteria and fungi that used to live inside them (shelanachium's pet theory!)

[AWK]

Heparin almost falls into your need

[shelanachium]

Heparin is a sulfate ester of the type ROSO3H so not a sulfonic acid; and though it contains NH2 groups these are not attached to sulfur so it is not a sulfonamide.

[AWK]

Heparin is a sulfate ester of the type ROSO3H so not a sulfonic acid; and though it contains NH2 groups these are not attached to sulfur so it is not a sulfonamide.

http://www.people.vcu.edu/~urdesai/hep.htm
http://en.wikipedia.org/wiki/Heparin
http://www.jbc.org/cgi/reprint/250/17/6841.pdf
http://www.rsc.org/ej/NP/2002/b100916h.pdf

[shelanachium]

Woops! Sorry, I didn't know about the -NHSO3- groups! That is indeed a sulfonamide.