Sceptrin, an antimicrobial agent from the sponge Agelas sceptrum

Sceptrin as a Potential Biosynthetic Precursor to Complex Pyrrole–Imidazole Alkaloids: The Total Synthesis of Ageliferin

“…A series of concerted bond shifts, as depicted in path C, can also account for this structural reorganization. Thus, tautomerization to intermediate 4 followed by a thermal [1,2] shift (4!5-membered ring), a hydride shift, another [1,2] shift (5!6-membered ring), and a final tautomerization could lead to 2. All three pathways could conceivably lead to the stereochemistry of 2 since the bromopyrrole-bearing carbon centers are incapable of epimerization and could therefore direct ring closure in paths A and B.…”

“…We also present an alternative biogenetic hypothesis commencing from 1 rather than 3 for other complex dimeric pyrrole-imidazole alkaloids, including the axinellamines [10] and palau'amines. [11] Our explorations began with several unsuccessful attempts to effect photochemical [1,3] sigmatropic rearrangement of 1. Thus, exposure of 1 to a 450-W Hanovia lamp (quartz or pyrex filter) for several days led only to gradual decomposition.…”

Chemical defenses of the Caribbean sponges Agelas wiedenmayeri and Agelas conifera

“…Isolation of brominated alkaloids from a specimen of Agelas wiedenmayeri, which had been collected in May 1998 at North Dry Rocks, Key Largo, was performed using a previously described procedure (Assmann et al 1999). The isolated bromopyrrole alkaloids of both A. conifera and A. wiedenmayeri were identified by comparison of mass spectrometry and NMR data with those previously reported (Forenza et al 1971, Garcia et al 1973, Walker et al 1981, Kobayashi et al 1990, Keifer et al 1991 as well as on the basis of 2D NMR data (COSY, HSQC, HMBC).…”

“…Besides these 2 brominated alkaloids, a series of dimeric bromopyrrole alkaloids, the sceptrins and ageliferins, have been isolated from A. conifera, A. sceptrum and A. sp. (Walker et al 1981, Kobayashi et al 1990, Keifer et al 1991. Although it was surmised that the dimeric brominated alkaloids found in other species of Agelas from the Caribbean deterred feeding , purified compounds were never tested.…”

Bromopyrrole alkaloids from the caribbean sponge Agelas cerebrum

“…18 It was not until 1981, during solidstate photodimerization studies of (-)-sceptrin, a related dimeric bromopyrrole alkaloid, that the final structure of 5 was confirmed by X-ray diffraction analysis. 19 Oroidin has been isolated from many Agelas sponges and species of other genera such as: Axinella damicornis, Axinella verrucosa, Acanthella aurantiaca, Goreauiella sp and Pseudaxinyssa cantharella. 20 Compound 4 (4,5-bromopyrrole-2-carboxylic acid) has been also isolated from many Agelas species and together with oroidin have been reported to exhibit significant biological properties.…”