Syntheses and PDT activity of new mono- and di-conjugated derivatives of chlorin e6.

Syntheses of three new chlorin e6 conjugates for PDT of tumors are reported. One of the new compounds 17 is conjugated with lysine at the 131-position, but the others are mono-conjugated 14 or diconjugated 15 with the non-amino acid species ethanolamine. Cellular experiments with the three new compounds and previously synthesized non-amino acid 152-conjugates (7-10), 131-monoconjugates 14, 16, and a 131,152-diconjugate 12 are reported. In vitro cytotoxicity experiments show that the 131-conjugates are more toxic than the 152-conjugates, and the most toxic derivative (dark- and photo-toxicity) is the 131-ethylenediamine conjugate 11. The most useful PDT photosentitizers appear to be the ethanolamine derivatives, conjugated at the 152- and the 131,152-positions; these show high phototoxicity but relatively low dark toxicity compared with 11, and also the highest dark/photo cytotoxicity ratios.

Investigation of the push-pull effects on ß-functionalized benzoporphyrins bearing an ethynylphenyl bridge.

A series of ß-pyrrole functionalized push-pull porphyrins with amine push groups linked via an ethynylphenyl spacer, and cyclic imide or carboxylic esters as pull groups have been newly synthesized and characterized. The ß-pyrrole functionalized ethynylphenyl spacer extends the conjugation of the porphyrin π-system, as reflected by their red-shifted absorbance and fluorescence spectra. The computed structures revealed no steric hindrance between the porphyrin π-system and the ß-substituents. The calculated HOMO and LUMO of compounds WJ2 and WJ3 display significant segregation, where the electron density in the HOMO and LUMO is mainly located at the donor component and the acceptor component, respectively. The orbital segregation is likely attributed to the introduction of the electron-donating amine group at the porphyrin periphery. Electrochemical studies revealed the expected lower HOMO-LUMO gap as a result of the facile oxidation and reduction of the push-pull porphyrins. As a consequence of the push-pull effects, a reduction in fluorescence intensity and lifetime was observed, especially for compound WJ3 having two electron-donating amino groups and a strongly electron-withdrawing cyclic imide group. Femtosecond transient absorption spectral studies revealed the successful formation of the singlet excited state in all of these push-pull porphyrins. Due to the occurrence of intramolecular charge transfer-type interactions, relaxation of the singlet excited state was found to be faster in compound WJ3 compared to other two derivatives in polar solvent but not in nonpolar solvent. Such charge transfer-type interactions from the triplet excited state were also observed in the case of compound WJ3 in benzonitrile. The present findings bring out the importance of push-pull effects in governing the ground and excited (singlet and triplet) state properties of free-base porphyrins.

Chlorin e6 131:152-Anhydride: A Key Intermediate in Conjugation Reactions of Chlorin e6.

Since the patent for the photodynamic therapy agent Talaporfin (mono-L-aspartylchlorin e6) was issued in 1987, confusion has existed regarding which of the three carboxylic acid groups in the chlorophyll degradation product, chlorin e6 (1), is modified in standard amino acid type conjugations (using DCC or EDC and an organic base) with amino acids and other biomolecules. Here it is shown that the site of conjugation is the central 152-carboxylic acid, such reactions proceeding in numerous examples via a 131,152-anhydride for which a high resolution X-ray structure is reported. Conjugation with eight oxygen and nitrogen nucleophiles, in every case, afforded the 152-conjugate, reinforcing the earlier conclusion that Talaporfin is the 152-aspartyl conjugate of chlorin e6 and suggesting that reports of 173-conjugation of chlorin e6 using stoichiometric peptide coupling procedures should be subjected to further scrutiny.