PAPER www.rsc.org/pps | Photochemical & Photobiological Sciences Glycerol and galactose substituted zinc phthalocyanines. Synthesis and photodynamic activity Yunus Zorlu, a Mahmut Ali Ermeydan, a Fabienne Dumoulin,* a Vefa Ahsen, a Huguette Savoie b and Ross W. Boyle* b Received 3rd October 2008, Accepted 12th December 2008 First published as an Advance Article on the web 14th January 2009 DOI: 10.1039/b817348f Three novel water soluble, non-ionic, zinc phthalocyanines (Pcs) have been synthesized and their spectroscopic and photodynamic properties investigated in aqueous media. One of the three compounds was shown to be significantly less aggregated, when compared to the other two compounds, and this effect was found to be related to both the nature of the substituent, and also the position at which it is attached to the macrocycle. Photodynamic activity and cellular uptake by human adenocarcinoma cells (HT-29) was shown to be linked to the aggregation state of the Pcs in water. Introduction Many metallated phthalocyanines (Pcs) are efficient photosensi- tisers, and when the macrocycle resulting from coordination of a metal or pseudo-metal results in a diamagnetic complex, such as with Zn(II), Al(III), Ga(III), Si(IV), excitation with visible light in the presence of molecular oxygen can result in the generation of reactive oxygen species via energy transfer from the triplet excited state of the Pc. If this reaction takes place when the Pc is associated with biological tissue or cells, oxidative damage to structural components including unsaturated lipids, amino acid residues and nucleic acids can occur, ultimately leading to cell death. This property is often exploited in the Photodynamic Therapy (PDT) 1 of cancer and other conditions such as age related macular degeneration. In order for Pcs to be useful photodynamic sensitizers it is necessary for them to be water soluble, or be formulated in a delivery vehicle which renders them water soluble. For this reason, and also because of their use as dyes, a large number of water soluble Pcs have been described. Commonly, water solubility is achieved by grafting ionic groups to the macrocycle, either axially or directly on the isoindoline sub-units. Most common amongst these are sulfonic acid groups, 2 resulting in anionic Pcs, and quaternarised amino 3,4 or pyridino 5–9 groups, which lead to cationic Pcs. The presence of polyoxoethylene 10 or hydroxyl 11 groups can also result in neutral water-soluble Pcs, and thus carbohydrates, which effectively allow multiple hydroxyl groups to be introduced as a single unit, are of great interest. Despite this fact, relatively few carbohydrate substituted Pcs have been described to date. Those that have been reported bear protected glycerol, 12–16 which can be considered as one of the most basic carbohydrates, or various hexoses in peripheral 17–21 or axial 22 positions; while very few have an asymmetric substitution pattern. 23–25 Among the few carbohydrate substituted Pcs for which properties as photodynamic sensitizers have been reported, three a Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze, 41400, Kocaeli, Turkey b Department of Chemistry, University of Hull, Kingston-upon-Hull, East Yorkshire, HU6 7RX, UK are silicon(IV) Pcs bearing solketal, 14 galactose 18 or glucose 22 units protected with acetal groups, and the fourth is a ZnPc peripherally substituted by eight solketal groups. 14,21 While axial substitution helps prevent aggregation, the solketal substitued Pcs are too hydrophobic to be fully soluble in water. The latter example, without axial ligands, is also highly aggregated in aqueous media. Aggregation has previously been shown to be linked to the photodynamic activity of hydroxylated and sulfonated ZnPcs. 11 In order to investigate the properties of Pcs subsituted by unprotected carbohydrates, which are likely to be much more soluble in water due to the free hydroxyl groups and thus more bioavailable, we prepared three tetrasubstituted Pcs bearing, respectively, galactose attached to the peripheral (4,5) positions of the isoindoline subunits (Fig. 1; 1) and glycerol either in peripheral (4,5) (Fig. 1; 2) or non peripheral (3,6) (Fig. 1; 3) positions. These compounds represent three new members of the rare class of non- ionic water-soluble Pcs. The coordinated metal, zinc, was chosen as hydroxyl ZnPcs have previously been shown to be efficient photodynamic sensitisers. 11,26 Results and discussion Phthalocyanine synthesis The synthesis of 1 was achieved by the cyclotetramerisation of the glycosylated phthalonitrile 7, itself prepared following Ziegler- Hanack’s glycosylation procedure 27 (Scheme 1). During the course of this work a report was published describing several new carbo- hydrate substituted Pcs, 20 however compound 1 was not among them. 1 therefore represents the first example of a Pc bearing galactose units linked to the macrocyle via the anomeric carbon. A series of well-known reactions in carbohydrate chemistry led to 5: galactose was perbenzoylated selectively to obtain only the pyrano derivative. Pentabenzoylated galactopyranose 4 was then selectively deprotected in the anomeric position with hydrazine acetate to give 5. Phthalonitrile 6 was obtained in 81% yield following Ziegler-Hanack’s new glycosylation method, which by condensation of anomeric hydroxyl with 4-nitrophthalonitrile 28,29 introduced a new route to formation of the glycosidic bond. We 312 | Photochem. Photobiol. Sci., 2009, 8, 312–318 This journal is © The Royal Society of Chemistry and Owner Societies 2009