Symbionts

1110

J. Nat. Prod. 2003, 66, 1110-1112

Defensive 2-Alkylpyrrole Sulfamates from the Marine Annelid Cirriformia tentaculata
Todd Barsby,† Cynthia E. Kicklighter,† Mark E. Hay,† M. Cameron Sullards,‡ and Julia Kubanek*,†,‡
School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332-0230, and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta,Georgia 30332-0400 Received April 2, 2003

Three novel 2-alkylpyrrole sulfamates (1-3) were isolated from the marine worm Cirriformia tentaculata. The structures were elucidated by the interpretation of spectral data obtained on inseparable mixtures of the unstable compounds. This suite of metabolites deterred feeding by the generalist predatory fish Thalassoma bifasciatum. A small array of naturalproducts have been identified from segmented marine worms, consisting predominately of peptides,1 pigments,2 halogenated aromatics,3 amino acids,4 nucleosides,4 and fatty acid derivatives.5 Some of these metabolites act as sex pheromones,4,5 whereas others have been hypothesized to defend worms against predators.6 However, direct tests of annelid natural products in feeding assays have notpreviously been reported. Herein we report the isolation and structure elucidation of three novel and unstable 2-alkylpyrrole sulfamates from the segmented marine worm Cirriformia tentaculata Montagu (Cirratulidae): 2-n-octylpyrrole sulfamate (1), 2-n-heptylpyrrole sulfamate (2), and 2-n-hexylpyrrole sulfamate (3), which to our knowledge comprise the first example of a confirmed chemical defense system ofa marine annelid and only the second example of a pyrrole sulfamate natural product.7,8 HMQC, and HMBC NMR spectral experiments and highresolution mass measurements. Another fraction composed predominantly of 3 decomposed too rapidly for acquisition of NMR or high-resolution mass spectral data.10 High-resolution mass measurements of the 1:1 mixture of 1 and 2 provided molecular formulas ofC12H20NO3S ([M]- 258.1163, calcd 258.1164) for 1 and C11H18NO3S ([M]244.1025, calcd 244.1007) for 2. Loss of sulfite from both 1 and 2 was evident from MS-MS daughter ions representing SO3•- and the alkyl pyrrole moieties (see Experimental Section). Additionally, low-intensity mass peaks offset by 2 amu, representing 34S at natural abundance, were observed by MS-MS for both parent ions and sulfitedaughter ions (but not for the alkyl pyrrole daughter ions), and thus confirmed the presence of sulfur in these natural products. Examination of the 1H and 13C NMR spectral data for the 1:2:1 mixture of 1-3 revealed a suite of coincidental downfield resonances indicative of a heteroaromatic moiety common to all three compounds. In addition, a group of aliphatic resonances in the 13C NMR methyleneregion (30-33 ppm) were sufficiently resolved to support a homologous relationship of 1-3. The 1H, COSY, HMQC, and HMBC data of the 1:1 mixture of 1 and 2 permitted the assignment of the heteroaromatic group as a substituted pyrrole. Three aromatic protons, with chemical shifts δ 5.82 (H-3; correlated by HMQC to δC 109.9), 5.89 (H-4; correlated by HMQC to δC 108.5), and δ 7.04 (H-5; correlated by HMQCto δC 122.3) all showed COSY correlations to each other. HMBC correlations from H-5 to C-2 (δC 137.3) and C-3, from H-3 to C-2 and C-5, and from H-4 to C-2, -3, and -5 supported a pyrrole monosubstituted at C-2, the only quaternary aromatic carbon. Proton couplings, including a pseudotriplet (J ) 3.2 Hz) for H-4, confirmed this substitution pattern. If the pyrrole had instead been substituted atC-3, H-4 would have possessed one J4 coupling, which for pyrroles is approximately 1-2 Hz,11 rather than the 3.2 Hz observed. Analysis of the remaining NMR resonances suggested an alkyl chain, attached to the quaternary carbon C-2. A methylene triplet (δΗ 2.88, H-1′; correlated by HMQC to δC 29.3) showed HMBC correlations to C-2 and C-3 in the pyrrole ring, and to C-2′ (δC 31.3) of the alkyl...