Certain varieties of puffer fish, Fugu in Japanese, are highly prized as foods in Japan. Since the v — Physical Chemistry Chemistry Question

Draw two resonance structures B and C.

Many derivatization reactions were performed in structure studies of tetrodotoxin. Treatment of tetrodotoxin (1) (see reaction scheme 1) with ethanolic potassium hydroxide upon heating afforded quinazoline derivative 2, which provided an insight into the nature of the fundamental skeleton of tetrodotoxin. The reaction mechanism can be described as follows. First, tetrodotoxin is hydrolyzed into carboxylate 3. Then the hydroxyl group highlighted with a frame is eliminated by the base to give intermediate D. A retro-aldol reaction of D cleaves a carbon-carbon bond to provide intermediates E and F. Finally, dehydration and aromatization from E produce quinazoline derivative 2.

Reaction scheme 1

Draw structures of the postulated intermediates D, E, and F.

Although biosynthesis of tetrodotoxin still remains to be clarified, it is proposed that tetrodotoxin may be biologically synthesized from L-arginine and isopentenyl diphosphate.

Among the carbon atoms included in tetrodotoxin, circle all those that are expected to be of isopentenyl diphosphate origin.

In the 1990s, an alternative biosynthetic pathway of tetrodotoxin was proposed. Condensation between 2-deoxy^-3-oxo^-D-pentose and guanidine provides intermediate G with cyclic guanidine moiety (molecular formula C₆H₁₁N₃O₃). Tetrodotoxin may be synthesized from G and isopentenyl diphosphate. Draw a structure of the postulated intermediate G showing the stereochemistry.