A palladium-catalyzed Sonogashira reaction has been developed for the highly efficient post-modification of ONNO “Salan” ligand and 2,6-dipicolinic acid stabilized titanium bis-chelates with anticancer activity. Different alkynyl substituents were introduced to “Salan” and 2,6-dipicolinic acid, respectively. In total 20 novel titanium complexes containing mono-, di- and tri-alkynyl substituents as well as a complex containing tumor targeting ethinylestradiol were synthesized, all complexes were characterized by ¹H NMR and ¹³C NMR, HRMS, UV-vis and IR spectroscopy. The nature of obtained titanium complexes that losing solvent molecules fast when exposed to air makes it hard to obtain satisfactory single crystals for X-ray diffraction measurement. Most alkynyl titanium complexes exhibit enhanced inhibitory activity against HeLa S3 and Hep G2 tumor cells in the micromole range. The introduction of alkynyl group to the Salan demonstrated less significant contribution to the anti-tumoral activity. However, the anti-tumoral activity alters with different alkynyl substituents on the 2,6-dipicolinic acid. Of all complexes, 3j [Salan^2,4-dimethylTi^(IV) Dipic^{4-(3-(dimethylamino)-prop-1-yn-1-yl)}] showed excellent inhibitory activity, its IC₅₀ value is an order of magnitude higher than that of Cisplatin, which is the most active anti-tumoral Salan titanium compound in this study [3j, HeLa S3: IC₅₀=(0.5±0.1) μmol/L, Hep G2: IC₅₀=(0.7±0.2) μmol/L; Cisplatin, HeLa S3: IC₅₀=(3.3±0.2) μmol/L, Hep G2: IC₅₀=(6.0±1.1) μmol/L]. In general, aromatic alkynyl substitution containing electron withdrawing moiety proved to have a positive influence on complex’s anti-tumoral activity than those containing electron donating moiety. Short chain aliphatic alkynyl substituents benefit the complex’s inhibitory activity. However, increased aliphatic chain length results in fast loss of complexes’ activity. Stability study on the representative aromatic alkynyl 2a, 3a and aliphatic alkynyl 2f, 3j suggests that the alkynyl’s electron nature can alter the complex stability. 2a and 2f, with substitutions on the Salan (2 position non-substituted), their half hydrolyzation time (t_1/2) are 5 and 10 h, respectively. The hydrolysate of 2a was characterized to be the non-toxic alkynyl Salan ligand 1a*. For 3a and 3j, the 2 position of Salan are occupied by methyl groups, their protective effect to the titanium center resulted in a stable behavior of both in the presence of an aqueous media. In addition, the “structure-activity” relationship and development prospects of these novel alkynyl Salan titanium bis-chelates are summarized and prospected.

Key words: Sonogashira reaction, [SalanTi^(IV)Dipic] complexes, antitumor activity, alkyne functionalization, aqueous stability