The title compound, C₁₅H₁₅NO, is an enantiopure small molecule, which has been synthesized many times, although its crystal structure was never determined. By recrystallization from a variety of solvent mixtures (pure acetonitrile, ethanol–water, toluene–ethanol, THF–methanol), we obtained three unsolvated polymorphs, in space groups P2₁ and P2₁2₁2₁. Form I is obtained from acetonitrile, without admixture of other forms, whereas forms II and III are obtained simultaneously by concomitant crystallizations from alcohol-based solvent mixtures. All forms share the same supramolecular structure, based on infinite C ₁ ¹(4) chain motifs formed by N—H...O intermolecular hydrogen bonds, as usual for non-sterically hindered amides. However, a conformational modification of the molecular structure, related to the rotation of the phenyl rings, alters the packing of the chains in the crystal structures. The orientation of the chain axis is perpendicular and parallel to the crystallographic twofold screw axis of space group P2₁ in forms I and II, respectively. As for form III, the asymmetric unit contains two independent molecules forming parallel chains in space group P2₁2₁2₁, and the crystal structure combines features of monoclinic forms I and II.

Research into muscle tissue pathologies offers great opportunities for new pharmaceutical agents. Current therapies, including corticosteroids and immunosuppressants, have limited efficacy and significant adverse effects. In this context, steroidal hydrazone compound 4d was investigated for its ability to promote muscle growth and regeneration as a potential anabolic and regenerative modulator. Flow cytometry analysis showed that 4d significantly increases cell populations in S phase, indicating a strong proliferative stimulus in pathways regulated by TNF-α, AKT, MAFbX, and SMAD2/3. Molecular docking studies showed that 4d shares strong interactions with the known MasR agonist (EP-2825), exhibiting a higher predicted binding affinity. Furthermore, 4d demonstrated the ability to interact with ACVR1/2A receptors, mimicking the binding profiles of known antagonists and potentially inhibiting myostatin/SMAD signaling. Taken together, experimental and computational evidence supports a dual-mechanistic model in which 4d promotes muscle proliferation and regeneration by (1) activating the MasR–PI3K/AKT/mTOR axis and (2) inhibiting the ACVR1/2A–SMAD pathway, counteracting the action of myostatin. These findings position compound 4d as a promising therapeutic candidate against muscle wasting disorders, including cancer-related cachexia, by inducing a robust and multifactorial anabolic response.

The title salt, C₁₄H₁₄N₃O₄S₂ ⁺·Cl⁻ [systematic name: 2-(4-hydroxy-2-methyl-1,1-dioxo-1,2-benzothiazine-3-amido)-5-methyl-1,3-thiazol-3-ium chloride] is the hydrochloride derivative of meloxicam, a drug used to treat pain and inflammation in rheumatic disorders and osteoarthritis. Although its molecular structure is similar to that previously reported for the hydrobromide analogue, both salts are not isomorphous. Different crystal structures originate from a conformational modification, arising from a degree of rotational freedom for the thiazolium ring in the cations. By taking as a reference the conformation of meloxicam, the thiazolium ring is twisted by 10.96 and −16.70° in the hydrochloride and hydrobromide salts, while the 1,2-benzothiazine core is a rigid scaffold. This behaviour could explain why meloxicam is a polymorphous compound.