Chondriamides A and B, two cytotoxic bis-indolic amhies were isolated from a red alga Chondria Sp. and their structures establishedfrom spectroscopic data. Red algae of the genus Ciwnakia are known for the production of cyclic polysulfides,' terpenoids,2" and novel aminoacids4*" A local new species of this genus grows abundantly on the rocky shores of the province of Buenos Aims, Argentina,'l and displays a very intense and unpleasant odor shortly after collection. Examination of an extract of this alga led to the isolation of compounds l-7.Fresh alga (2 kg wet weight, collected intertidally at Miramar, Buenos Aires Argentina) was extracted with EtOH (2 x 21) and CHzCl2 (2 x 21) shortly after collection and the extracts concentrated at reduced pressure. The resulting aqueous suspension was partitioned between AcOEt and water. The organic layer was taken to dryness and the crude extract (1 lg) was fractionated by flash chromatography on silica gel. The fractions which contained aromatic compounds were chromatographed on Sephadex LH-20 (methanol). Compounds 1,3 and 4 were purified in this way, Final purification of compounds 2 and 7 was achieved by preparative TLC on silica (CH~Clz/Acetone 80:20) while the same technique was used (CH2ClZ/Acetone 1: 1) for the purification of 5 and 6. Compound 1 was identified as indole-3-carboxahlehyde by comparison with an authentic sample.Compound 2 (30 mg),* has a molecular formula C12Hlo02N2 established by HRMS. NMR spectra indicated the presence of a 3-substituted indole nucleus conjugated with a disubstituted double bond. A signal at 69.19 (d, lH, J=9.6) coupled to an interchangeable proton, together with the IR spectrum, suggested that this compound could be a fonnyl imide. Final proof of the structure was obtained by analysis of the EIMS fragmentations at 20 eV.9Chondriamide A (3) (120 mg),*'has a molecular formula C21HlfiN3 estabished by HRMS. The 'H NMR spectrum showed clearly the presence of two different 3-substituted indole nucleus, each of them conjugated with a different trans-disubstituted double bond. One of these double bonds showed as a pair of doublets at 6 6.75 and 7.92 (J=16 Hz), while the other showed as a doublet at 6 6.49 (J=15 Hz) coupled to a double doublet at 6 7.68 (J=15;9 Hz) which in turn was coupled to an amide proton at 6 9.65 (bd, J=9 Hz). These features were confirmed by decoupling experiments. On addition of D20 the signal at 6 7.68 collapses to a doublet (J=15 Hz). The presence of an a\$ unsaturated amide carbonyl group was ascertained by 13C NMR (6 165.4). The above features suggested a structure consisting of an indolic unsaturated amide of indoleacrylic acid, which was confirmed by ElMS at 20 eV. The fragments at m/z 170 and m/z 186 were clearly originated in the breaking of the C-N bonds of the amide system thus continning the proposed strucure for compound 3. All the previous assignments were confkrned by 2Il NMR (COSY and CSCM) experiments.Chondriamide B (4) (80 mg)," has a molecular formula CzlHle established by HRMS The 'H NMR spectrum indicated again the presence of two different indole nucleus, while the EIMS at 20 eV of (4) showed a similar fragmentation pattern than that of (3), with the addition of a hydroxyl group on the indoleacrylic acid portion of the amide. The presence of an aromatic hydroxyl group was confirmed by 13C WMR (6144.7) and 'H NMR (59.15, bs. interchangeable) spectra.The pattern of the aromatic region in the 'H NMR spectrum showed the presence of three consecutive protons, indicating that the hydroxyl should be placed either in position 4 or 7. The large upfield shift (0.5 ppm) experienced by protons 4 and 6 clearly indicated that the hydroxyl group should be placgd in position 7. The assignments of the 'H and 13C NMR spectra were confirmed by 2D (CCSY and CSCM) NMR experiments.From a mote polar fraction the two acidic precursors of chondriamides A and B were isolated, namely 3- indoleacrylic acid (5) (15 mg) and 7-hydroxy-3-indoleacrylic acid (6) (9 mg) respectively. A minor compound (7) (3 mg) isolated from this alga was identified as the ethyl ester of 3-indoleacryltryptophan.12 The ethyl ester group is clearly an artifact formed with the ethanol used for the extraction, but indicates that the free acid, 3-indoleacryltryptophan (which could not be detected) is the biosynthetic precursor of chondriamide A.The imide 2 and the aldehyde 1 art: possible oxidation products of 3. When a methanolic solution of compound 3 is left standing overnight, compounds 1 and 2 arc formed. However, the ocurrence of a similar process in the living organism cannot bc ruled out since this alga is exposed to the air and direct sunlight quite frequently during low tides.Qtotoxicity assay results for compounds 3 and 4 were the following: chondriamide A (3) was active at a cont. of 0.5 ~.t.ghnl against KB cells and 5 Pg/ml against LOVO cells (colon cancer), while chondriamide B (4) was active at cl @ml (KB) and 10 Pam1 (LOVO). Chondriamide A (3) shows antiviral activity against HSV II at l&ml. Chondriamide B (4) shows mild antifungal activity against Aspergillus oryzae (6 mm inhibition zone at 250 ~&iisk) and Trichophyton mentagrophytes (11 mm zone at 250 @disk)