Tetrahedron Letters,Vo1.30,No.33,pp 4359-4362,1989 0040-4039/89 $3.00 + .OO Printed in Great Britain Perqamon Press plc zyxwvutsrqpo NEW CYTOTOXIC ACRIDINE ALKALOIDS FROM TWO DEEP WATER MARINE SPONGES OF THE FAMILY Pachustrellidue Geewananda P. Gunawardand, Shigeo Kohmoto, and Neal S. Burres Divsion of Biomedical Marine Research, Harbor Branch Oceanographic Institution, Inc. 5600 Old Dixie Highway, Fort Pierce, Florida 34946, USA Fused ring alkaloids having the pyrido[4,3,2-mnlacridine skeleton comprise a new class of marine natural products.laeh Their biological activityle and challenging structure elucidation make them an interesting group zyxwvutsr of cumpoundr. In this paper we report the identification of four new cytotoxic and structaraUy related alkaloid. nordercitin (I), dercitamine {2), dercitamide (3), and cyclodercitin (4). The extracts of two sponges, a deep violet Dercitus sp. and a red Stelletta sp., collected by manned submersible at depths of 152m and 70m respectively, in the Bahamas,2 inhibited growth of murine P388 leukemia cells when screened on shipboard at the site of collection. The organisms were kept frozen until extraction with MeOH:toluene (3:l) and 100% MeOH. Fractionation of the Dercitus extract by centrifugal countercurrent chromatography using MeOH:CH$12:Hz0(5:5:3) gave the previously described dercitin (5) as the major antitumor alkaloid.te Further purification of the fractions containing minor metabolites by HPLC (NH, stationary phase, solvent system - CHsCN: MeOH: CHzC12(4:4:1) containing 1% NH,OH) gave cyclodercitin (4), and two N-oxides of dercitin(N-1 and N-15). Using similar chromatographic procedures, the extract from Stetleta sp. gave nordercitin (1). dercitamine (Z), and dercitamide (3). The pyrido[4,3,2-mn]thiazolo[3,2-b]acridinium-9-ethyl skeleton (Figure 1) in each compound was suggested by the characteristic UV absorption pattern, (&,, (MeOH) 245 (t 13,800), 307 (t l&900), and 361 nm (t 39OO)), which was highly sensitive to the pH of the medium. Further, the aromatic region of the ‘H nmr spectra of each compound consisted of seven signals: a downfield one proton singlet for the thiazole proton (H-l I), two vicinal olefin proton signals (H-2 and H-3) and signals for four protons on an ortho disubstituted aromatic ring (H-4 - H-7). In the aliphatic region signals for two vicinal methylene groups were observed. Three bond CH connectivities for all the carbons except for C-12c could be observed in spectra from COLOC3 and HMB@ experiments (Table 1). Comparison of the ‘H and t3C spectra (Tables I & 2) of the four compounds showed that they differed from dercitin (5) in the substituents on N-l and/or on the ethyl side chain. The presence of a methyl function on N-l in 4 - 6 could be readily detected by a 3 proton singlet observed at 3.5 to 3.9 ppm in CD,OD or between 4 to 5.6 ppm in TPA-d and a corresponding carbon signal observed between 44 to 52 ppm in either solvent. The N-l methyl protons also showed 3-bond connectivity to C-2 and C-12b. Further, the presence of a methyl group on N-l could be deduced from the color of the compound in solution: both types turn deep red to violet(480-510 nm) in acidic medium, but the N-methylated compounds turn blue (590 nm) in basic medium while the others turn yellow (430nm). 4359