Identify the functional groups of Tetrdotoxin and it is soluble in water or not.

This should help:

Pure tetrodotoxin is a colorless crystalline powder. It darkens above 220° C. without decomposition. There are several hydrophilic hydroxyl groups in tetrodotoxin, making it insoluble in organic solvents. Its molecular skeleton is similar with the cage structure of adamantane, making hydration very difficult, thus it is just slightly soluble in water. Because there is a guanidine perhydroquinazoline group in the molecule, and guanidine group is strongly alkaline, tetrodotoxin is soluble in water solutions of acids. Because tetrodotoxin also has the structure of inner ester, and water solutions of strong acid will make it decompose, the only way to keep it stable in solution is to dissolve it in a solution of weak organic acid. The particularity of C-4 can be easily seen from the molecular structure of tetrodotoxin. C-4 is in the ortho-position of the nitrogen atom with OH group at equatorial position and H atom at axial position. Therefore, the chemical and biological activities of the hydroxyl group on C-4 are significant. If H+ is present in the solution, the oxygen atom from the hydroxyl group of C-4 will combine with it, and produces positively charged structure B from structure A. Structure B losses a H20 molecule and result in structure C with positively charged C-4.

Structure C may interact with H2O in the solution. The H2O can either attack the position where the original H2O molecule is eliminated so that structure E is derived, or attack the opposite position where the H2O molecule is eliminated so that structure D is derived. If a H2O molecule is removed from structure E, the original tetrodotoxin structure A is produced. Structure D will lead to structure F after a H2O is removed. The difference between structure F and A is that the positions of H and OH are exchanged. The H on C-4 of structure A is axial and OH is equatorial, while in structure F the H on C-4 is equatorial and OH is axial.


Assuming ones that are nonpolar.