General Papers ARKIVOC 2007 (xv) 225-231 ISSN 1551-7012 Page 225 © ARKAT USA, Inc. Indole alkaloid from the Red Sea sponge Hyrtios erectus Mohamed A. Ashour, a Ehab S. Elkhayat, b * Rainer Ebel, c RuAngelie Edrada, c and Peter Proksch c a Faculty of Pharmacy, Al-Azhar University, Pharamcognosy Department, Cairo, Egypt b Faculty of Pharmacy, Al-Azhar University, Pharamcognosy Department, Assiut 71524, Egypt c Institut für Pharmazeutische Biologie, Heinrich-Heine-Universität, Universitätsstr 1, 40225 Düsseldorf, Germany E-mail: Khayat71@yahoo.com Abstract Indole-3-carbaldehyde and 5-deoxyhyrtiosine A are reporterd for the first time in the genus Hertios, in addition to other indole alkaloids and three scalarane sesterterpenes, from the Red Sea sponge Hertios erectus. The isolated compounds were tested for their cytotoxic and antimicrobial activities. Keywords: Hertios erectus, indole alkaloids, indole 3- carbaldehyde, 5-deoxyhyrtiosine A Introduction The secondary metabolites from the genus Hyrtios particularly Hertios erectus (synonym H. erecta) have been investigated extensively 1-5 . Previous chemical investigations of different Hyrtios sp. and their associated microorganisms revealed the presence of numerous structurally unique natural products including scalarane sesterterpenes, acyclic triterpenes, indole alkaloids, and macrolides in addition to steroids. Many of these compounds possess interesting biological activities. Spongistatins, the most important metabolites of the genus Hyrtios discovered to date, showed powerful anticancer activity 6,7 , which encouraged an exhaustive recollection of the H. erecta sponge (600 kg wet wt.) for further chemical investigations, which afforded the antineoplastic agents sesterstatins 8-10 . In the present study, H. erectus collected from the Red Sea – Egypt was chemically investigated and a series of indole alkaloids were isolated, deoxyhyrtiosine A (1) and indole-3- carbaldehyde (2) isolated for the first time from the genus Hyrtios; in addition to the known indoles; 5-hydroxy-1H-indole-3-carboxylic acid methyl ester (3), 5-hydroxy-1H-indole-3- carbaldehyde (4) and hyrtiosine A (5) were obtained. Three scalarane sesterterpenes: 16- hydroxyscalarolide (6), scalarolide (7) and 12-O-deacetyl-12-epi-scalarine (8), besides 5α,8α-