Methods of pyridylporphyrin oxidation and synthesis

Porfirini su organski spojevi koji se mogu koristiti kao fotoosjetljivi spojevi (PS) u fotodinamičkoj terapiji (PDT). PDT uključuje administraciju PS-a u tijelo, gdje se isti lokalizira u tumorskom tkivu te, nakon osvjetljavanja svjetlošću određene valne duljine, uzrokuje odumiranje tumorskog tkiva. Najčešća metoda sinteze porfirina u našem laboratoriju je modificirana Adler- Longo reakcija koja se relativno jednostavno izvodi, brza je i daje nečistoće koje se mogu pročistiti stupčanom kromatografijom. Zwitterionski oksidirani porfirini imaju malu toksičnost u “mraku”, što je bitno za fotodinamičku terapiju (PDT), u usporedbi sa svojim kationskim analozina, N-metiliranim piridilporfirinima. Stoga, smo naše istraživanje usmjerili na proučavanje upravo ove grupe porfirinskih PS-ova. Jedan od zahtjeva za porfirine koji se efikasno primjenjuju u PDT, je njihov visoki unos u ciljane stanice. Stoga, N-oksidirani piridilporfirini koji su nam od interesa imaju lipofilnu komponentu, a njihova sinteza u okviru ovog istraživanja uključuje adiciju dugih alkilnih lanaca koji potječu od dodekanoil klorida ili heksadekanoil klorida. U ovom radu, različite metode N-oksidacije piridilporfirina su analizirane kako bi se istražilo koja metoda rezultira najvećim iskorištenjem oksidiranih porfirina s minimalnom prisutnošću nečistoća za potencijalnu primjenu u PDT-u. Četiri analizirane metode uključuju N-oksidaciju pomoću: meta- kloroperbenzojeve kiseline (m- CPBA); dimetildioksirana (DMD); hodikovog peroksida, natrijeva hidroksida i meta- kloroperbenzojeve kiseline; ili pomoću octene kiseline. Samo su se metode N-oksidacije pomoću m-CPBA i DMD-a pokazale optimalnima, jer su rezultirale visokim iskorištenjem piridilporfirina (65 % za m-CPBA i 70 % za DMD) u reakcijama koje su se lagano mogle optimizirati i izvesti. Metoda koja uključuje upotrebu H2O2, NaOH i m-CPBA, dala je iskorištenje od 3,92% a reakcija s CH3COOH nije dala produkte. UV/Vis spektroskopska analiza nije pokazala razliku između spektara simetričnog porfirina oksidiranima upotrebom različitih metoda. Zaključak istraživanja jest kako metoda 1 (m-CPBA) i 2 (DMD) daju zadovoljavajuća iskorištenja. Iako je oksidacija metodom 2 zahtjevnija zbog potrebe za stalnim podešavanjem pH vrijednosti, daje produkt s manje onečišćenja, te je iskorištenje veće za do 5%.Porphyrins are organic compounds that can be used as photosensitizers in photodynamic therapy (PDT). PDT involves photosensitizer (PS) administration into the body, where they penetrate tumour tissues and, once illuminated, cause tumour degradation. Most common way of porphyrin synthesis in our laboratory includes modified Adler-Longo method, since it is relatively easy to conduct, it is fast and gives us products with impurities separable with a column chromatography. Recently we have found that zwitterionic N-oxidised pyridylporphyrins as PSs in PDT exhibit low “dark” toxicity, as opposed to their cationic analogues, N-methylated pyridylporphyrins, thus we decided to focus our research on this perspective group of porphyrin PSs. One of the requirements for porphyrins to be used in PDT efficiently, is their high uptake into targeted cells. Therefore, N-oxidised pyridylporphyrins we are particularly interested in have lipophilic component, and their synthesis in this work includes adding long alkyl chains derived from dodecanoyl and hexadecanoyl chlorides. In this work different methods of pyridylporphyrin N-oxidation were analysed to investigate which method is the best in terms of yields and ease of purification for preparation of new potential photosensitisers for the use in PDT. Four methods were assessed for N-oxidations of porphyrins using: meta-chloroperoxybenzoic acid (m-CPBA), dimethyldioxirane (DMD); hydrogen peroxide, sodium hydroxide and meta-chloroperoxybenzoic acid; or acetic acid. Only methods using m-CPBA and DMD showed promising results, providing high yields of oxidised pyridylporphyrins (65 % for m-CPBA and 70 % for DMD) in the reactions that were easy to optimize and conduct. Method including H2O2, NaOH and m-CPBA gave a yield of (oxydo)pyridylporphyrin of 3,92 % and the reaction using CH3COOH did not occur. UV/ Vis spectroscopic analysis showed no difference between the spectra of symmetric porphyrin oxidised by the different methods. We are concluding from this work that both methods 1 (m-CPBA) and 2 (DMD) provide good yields. Although method 2 is more complicated to perform due to constant pH adjustments, the product contains less impurities, needs less additional purification and the yield is up to 5 % higher in comparison to the method 1