*3.3. Aqueous Solubilities*

One of the main objectives of conducting salt/cocrystal screenings of active molecules is to find suitable candidates with the best physical-chemical properties. In a previous work, we described two new hydrated salts (malonate and fumarate) and an anhydrous succinate of 9ETADE [18]. Herein, the aqueous solubilities of 9-ethyladenine and the three anhydrous candidates (the two anhydrous oxalate salts prepared in this work and the succinate salt of 9ETADE) were determined for comparative purposes (Table 2).

**Table 2.** Aqueous solubilities of the succinate salt, compounds **1** and **3** and the precursors.


\* Sigma-Aldrich.

From these results, the modified nucleobase showed the highest solubility in water in comparison to the other salts or even the former carboxylic acids used. Although the results did not indicate an improvement in the solubility behavior of the new compounds, it shows that it is possible to modulate this property, resulting apparently the 9ETADE-OXA (1:1) solid form the most soluble of the three studied salts.

The undissolved residues were analyzed by PXRD. It is worth noting that the compound **1** had transformed partially to the 2:1 salt, compound **3**. Thus, this case is a new example of a solvent-mediated phase transformation and the solubility value obtained for this compound should be discarded. Nevertheless, the results obtained indicated that the powder patterns for this compound **3** and the succinate (1:1) salt remained undisturbed (Figure S8).
