in the beta-pyrrolic positions; the results already obtained show that this type of PSs is also very promising.This fact, and our nding of an easy synthesis for porphyrin 1a (see Fig. 1) bearing a terpyridine unit in the beta pyrrolic position, 35 prompted us to expand the studies to the syntheses of the analogues 1b and 1c in order to use them as templates for further cationization. So, herein, we report the synthesis and the characterization of a series of neutral and cationic porphyrins bearing terpyridine units in one of their beta-pyrrolic positions. In the course of the characterization of these compounds we found that isomer differentiation of the cationic compounds could be easily achieved by ESI-MS (electrospray mass spectrometry).Additionally, their efficacy on the photoinactivation of bioluminescent E. coli was evaluated. The bioluminescent genetically transformed E. coli was selected as a model of Gramnegative bacteria to monitor in real-time photodynamic inactivation through bioluminescence measurement, thus avoiding the laborious and time-consuming conventional method of counting colony-forming units.
Results and discussion
Synthesis of neutral derivativesThe synthetic strategy to obtain the new b-pyrrolic cationic derivatives 6 and 7 (see Scheme 2) required the previous preparation of the corresponding neutral derivatives according with experimental work summarized in Scheme 1. The access to the new neutral porphyrins 1b and 1c bearing the terpyridine units in the b-pyrrolic positions involved the Kröhnke type approach described previously for the synthesis of porphyrin 1a. 35 In this methodology the terpyridine moiety was built directly from the easy accessible 2-formyl-5,10,15,20-porphyrin (TPP-CHO) 36 by reaction with 2-acetylpyridine (5 equiv.) in the presence of ammonium acetate (8 equiv.) and La(OTf) 3 (20 mol%).35 The procedure led to compound 1a in good yield (45%) affording as minor compounds the benzoporphyrin 2a (29%) and the porphyrin-chalcone 3a (10%) ( Table 1, entry 1).Based on that synthetic strategy we envisaged, just by changing the 2-acetylpyridine by the adequate 3-and 4-acetylpyridine the syntheses of the new neutral terpyridine derivatives 1b and 1c.In order to force the formation of the desired terpyridine 1a, the reaction was repeated in the presence of 2-acetylpyridine during 4 h. The results summarized in Table 1 (entry 2) show that the expected derivatives 1a, 2a and 3a were isolated in yields similar to our previously used conditions. However, a careful analysis of TLC data allowed us to detect a minor and more polar red product. Aer purication, the structure of this product, obtained in 4% yield, was established based on spectroscopic data (see infra and also ESI †) as the new 2-(2,4-diarylpyridin-6-yl)-5,10,15,20-tetraphenylporphyrin 4 (Fig. 2).Attempts to improve compound 4 yield by increasing the reaction time were not successful. The formation of the new derivative 4 can be explained in a similar manner as the one proposed for derivative 1a, 35 using as template...