Stereoisomers of 42-Hydroxy Palytoxin from Hawaiian Palythoa toxica and P. tuberculosa: Stereostructure Elucidation, Detection, and Biological Activities Patrizia Ciminiello, † Carmela Dell’Aversano, † Emma Dello Iacovo, † Martino Forino,* ,† Luciana Tartaglione, † Marco Pelin, ‡ Silvio Sosa, ‡ Aurelia Tubaro, ‡ O. Chaloin, § Mark Poli, ⊥ and Gary Bignami ∥ † Department of Pharmacy, University of Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy ‡ Department of Life Sciences, University of Trieste, Via A. Valerio 6, 34127 Trieste, Italy § CNRS, Institut de Biologie Molé culaire et Cellulaire, Laboratoire d’Immunologie et Chimie The ́ rapeutiques, 67000 Strasbourg, France ⊥ U.S. Army Medical Research Institute of Infectious Diseases, Ft Detrick, Maryland 21701-5011, United States ∥ Bignami Consulting, Honolulu, Hawaii, United States * S Supporting Information ABSTRACT: Palytoxin ranks among the most potent marine biotoxins. Its lethality was well known to native Hawaiians that used to smear a “moss” containing the toxin on their spears to cause instant death to their victims. Human intoxications due to exposure to palytoxin and to its many congeners have been reported worldwide. Currently, palytoxins constitute the main threat to public health across the Mediterranean Sea. In the present work we report on the isolation and stereostructural determination of a new palytoxin analogue from a Hawaiian Palythoa tuberculosa sample. This new toxin is a stereoisomer of 42-hydroxypalytoxin isolated from Palythoa toxica. The whole absolute configuration of this latter toxin is also reported in the paper. Interestingly, the two 42-hydroxypalytoxins do not share the same biological activity. The stereoisomer from P. tuberculosa showed cytotoxicity toward skin HaCaT keratinocytes approximately 1 order of magnitude lower than that of 42- hydroxypalytoxin from P. toxica and about 2 orders of magnitude lower than that of palytoxin itself. This finding holds the prospect of interesting structure−activity relationship evaluations in the future. I n 1961, Philip Helfrich, accompanied by John Shupe, tracked down a legendary tidepool near the village of Mu’olea on the Island of Maui, where native Hawaiians used to collect a deadly seaweed reportedly capable of causing instant death to prey or enemies. 1−3 Analyses of samples collected from this tidepool revealed the organism responsible for the fabled lethality to be a new species of cnidarian zoanthid, known as Palythoa toxica,a very rare species sparingly found along the Pacific coasts. 4,5 In 1971, Paul Scheuer and Richard Moore isolated the toxic molecule from samples of P. toxica and provided preliminary details about its chemical structure. The toxin was named palytoxin (1). 2 It took more than 10 years to fully define the stereochemical architecture of palytoxin. 6−8 In 1972, palytoxin was also isolated from Palythoa tuberculosa collected from Okinawa, Japan. 4 Since then, toxins seemingly identical to palytoxin have been identified in other Palythoa species from around the world, such as P. vestitus from Hawaii, 9 P. caribaeorum from the West Indian islands, 10 and additional unidentified Palythoa spp. from Tahiti and Japan. 11 It is known that palytoxins can differ structurally from each other depending upon their biological sources and geographical provenance. Additionally, level and content of palytoxins in toxic Palythoa spp. can vary significantly among species, among populations of the same species, and seasonally. 12 In 2009, we published a paper reporting on the analysis of the toxin content of two samples of Hawaiian P. tuberculosa and P. toxica. 13 These samples were collected along the Hawaiian coasts and stored at the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick, Maryland. 14 In-depth high resolution liquid chromatography−mass spectrometry (HR LC/MS) analysis allowed identification of a previously undescribed palytoxin-like compound in both samples of Palythoa spp. Interestingly, this new palytoxin analogue was found to be by far the main palytoxin derivative present in the P. toxica sample and a major component of the toxic extract of the P. tuberculosa sample, alongside palytoxin itself. By 1D- and 2D-NMR investigation, we structurally characterized the toxin Received: November 19, 2013 Published: February 10, 2014 Article pubs.acs.org/jnp © 2014 American Chemical Society and American Society of Pharmacognosy 351 dx.doi.org/10.1021/np4009514 | J. Nat. Prod. 2014, 77, 351−357