338

26 G. L. Elizarova, L. G. Matvienko, N. V. Lozhkina and V. N. Parmon, React. Kinet. Cutal. Lett., 26 (1984) 67-72.

27 G. L. Elizarova, L. G. Matvienko, N. V. Lozhkina, V. N. Parmon and E. M. Moroz, IN. Sib. Otd. Akod. Nauk SSSR, Ser. Khim. Nauk (1990) 86-93.

28 S. V. Lymar, V. N. Parmon and K. I. Zamaraev, in J. Mattay (ed.), Photoinduced electron transfer ZZZ: Topics in Current Chemistry, Springer, Berlin, 159 (1991) l-65.

29 I. M. Tsvetkov, S. V. Lymar, V. N. Parmon and K. I. Zamaraev, Z&et. Z&t&, 27 (1986) 109-116.

30 N. P. Luneva, Ye. I. Knerelman, V. Ya. Shafirovich and A. E. Shilov, J. Chem. Sot. Chem. Comm., (1987) 1504-1505.

31 0. V. Gerasimov, I. M. Tsvetkov, S. V. Lymar and V. N. Parmon, React. &et. Cut& Lett., 36 (1988) 145-149.

32 Ye. I. Knerelman and V. Ya. Shafirovich, finet. Kataf., 28 (1987) 1237-1239. 33 J. R. Darwent, P. Douglas, A. Harriman, G. Porter and M.-C. Richoux, Coord. Chem. Rev.,

44 (1982) 83-126. 34 P. A. Chistensen, A. Harriman, G. Porter and P. Neta, J. Chem. Sot., Faraday Trans. 2, 80

(1984) 1451-1464. 35 G. S. Nahor, S. Mosseri, P. Neta and A. Harriman, 1 Phys. Chem., 92 (1988) 4499-4504. 36 0. V. Gerasimov, S. V. Lyrnar and V. N. Parmon, J. Photochem. Photobiol. A: Chem., 56

(1991) 275-285.

Structural analysis of HPD

David Kessel

Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI 48201

(USA)

One of the mysteries concerning the tumor-localizing product HPD (hematopor- phyrin derivative) is the ability of HPD components to persist for weeks in tissues after administration, in spite of a high degree of water solubility. In a recent report, Mironov et al. [l] provided some data concerning the relative numbers of porphyrin rings in HPD which occur as monomers, dimers and higher oligomers. Alkaline hydrolysis delineated ester from ether linkages. Based on this report, it is possible to make some calculations concerning the ether US. ester linkages in the HPD preparation employed in this study.

Fresh HPD consists mainly of ester linkages, but during subsequent treatment, we have suggested that unhydrolyzed acetate groups form ether linkages [2]. Among the unknown factors is the nature of the mechanism whereby many of the ester linkages in HPD are protected from alkaline hydrolysis in aqueous solution. Pandey et nl. [3] have shown that simple porphyrin diesters cannot survive even mild alkali, and the formation of HPD calls for treatment of HP acetates with 0.1 M NaOH. In the purification step leading to Photofrin II, additional treatment at pH 9 results in a product which contains both ester and ether linkages in the dimer/oligomer fraction

[41.

339

Assuming that the relative percentages described by Mironov et al. refer to numbers of porphyrin rings in each category, 23% of HPD is in monomeric form before hydrolysis and 53% after. This result implies that 30% of the dimer/oligomer rings were joined by ester linkages, and 47% by ether linkages. Since the higher oligomers contained 57% of the total rings before hydrolysis and 17% after, 17% of the oligomer rings were in an ether configuration involving three or more joined rings, and 40% of the oligomer rings were initially contained in an ester linkage.

Additional insights into the nature of HPD are a matter of speculation, since the dimer data are difficult to interpret. An unambiguous answer could be obtained by separating the dimer and oligomer fractions from the Fractogel column and subjecting these to alkaline hydrolysis. The initial dimer fraction contained 20% of the total porphyrin rings, but after hydrolysis this number increased to 30%, with the difference derived from oligomeric diethers initially joined by one or more ester linkages to additional rings. Any ester dimers should have been converted into monomers during HPD synthesis.

Spikes recently reported on some possible definitions of the term HPD [5]. In retrospect, perhaps Sam Schwartz should have called it PRU (Porphyrins R Us).

1 A. F. Mironov, A. N. Nizhnik and A. Yu. Nockel, J. Photochem. Photobiol. B: Biol., 6 (1990) 337-341.

2 D. Kessel, P. Thompson, B. Musselman and C. K. Chang, Cancer Res., 47 (1987) 4642-4645. 3 R. K. Pandey and T. J. Dougherty, Cancer Res., 49 (1989) 2042-2047. 4 R. K. Pandey, M. M. Siegel, R. Tsao, J. H. McReynolds and T. J. Dougherty, Biomed.

Environ. Mass Spec., 19 (1990) 405-414. 5 J. Spikes, J. Photochem. Photobiol. B: Biol., 20 (1991) 371-372.