The nfkb2 gene is a member of the Rel/NF-κB family of transcription factors. COOH-terminal deletions and rearrangements of this gene have been associated with the development of human cutaneous T cell lymphomas, chronic lymphocytic leukemias, and multiple myelomas. To further investigate the function of NF-κB2, we have generated mutant mice carrying a germline mutation of the nfkb2 gene by homologous recombination. NF-κB2–deficient mice showed a marked reduction in the B cell compartment in spleen, bone marrow, and lymph nodes. Moreover, spleen and lymph nodes of mutant mice presented an altered architecture, characterized by diffuse, irregular B cell areas and the absence of discrete perifollicular marginal and mantle zones; the formation of secondary germinal centers in spleen was also impaired. Proliferation of NF-κB2–deficient B cells was moderately reduced in response to lipopolysaccharide, anti-IgD-dextran, and CD40, but maturation and immunoglobulin switching were normal. However, nfkb2 (−/−) animals presented a deficient immunological response to T cell–dependent and –independent antigens. These findings indicate an important role of NF-κB2 in the maintenance of the peripheral B cell population, humoral responses, and normal spleen architecture.

Three diterpene-benzoate natural products, with novel carbon skeletons and an unusual proposed biosynthesis, were isolated from extracts of the Fijian red alga Callophycus serratus and identified by a combination of X-ray crystallographic, NMR, and mass spectral analyses. Bromophycolide A (1) displayed cytotoxicity against several human tumor cell lines via specific apoptotic cell death. This represents the first discovery of natural products incorporating a diterpene and benzoate skeleton into a macrolide system.The discovery of novel carbon skeletons in natural products research is uncommon, providing new targets for synthetic chemists and pharmacologists, and leading to testable hypotheses regarding biosynthetic mechanisms and ecological function. Red macroalgae are well-known for the production of brominated metabolites, including terpenoids and phenols, yet some taxa within the Rhodophyta remain relatively unstudied. Only six secondary metabolites, one oxylipin and five bromophenols, have been previously characterized from the red algal family Solieriaceae. 1,2 Herein, we report the discovery of a unique structural class of macrolides from Callophycus serratus, an understudied member of the Solieriaceae.We used bioassay-guided fractionation followed by spectroscopic and X-ray crystallographic analyses to identify three novel natural products (1-3) of unusual biosynthetic origin and possessing promising antineoplastic and antimicrobial activities. Supporting Information Available: Additional acknowledgments, experimental details, 2D NMR data (COSY, HSQC, HMBC, NOESY, ROESY), 1 H NMR spectra for 1-3, and X-ray crystallographic data (tables and CIF files) for 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org. The most abundant natural product from C. serratus, bromophycolide A (1), displayed an [M -H] − molecular ion with m/z 661.0194 and characteristic tribrominated isotopic pattern, suitable for a molecular formula of C 27 H 37 O 4 Br 3 . X-ray diffraction analysis of 1 revealed a 15-membered macrolide within a diterpene-benzoate framework (Figures 1 and 2). The bromine atom within the isopropyl appendage was disordered with respect to the isopropyl methyls over two primary positions, with 70% and 30% occupancies. The Flack parameter was refined to be −0.002(16), indicating that the geometry shown is the absolute configuration. NIH Public AccessThe NMR spectral data of 1 supported the structure derived from X-ray diffraction analysis (Table 1; Supporting Information). HMBC correlations from the methyl groups anchored the carbon skeleton, enabling assignments of all quaternary carbons. COSY and additional HMBC correlations provided the connectivity within spin systems (Supporting Information).From high-resolution mass spectral data, bromophycolide B (2) appeared to be an isomer of 1, with a parent ion with m/z 661.0191. X-ray diffraction analysis of 2 indicated a 16-membered macrolide with absolute stereochemistry predicted as in Figures 1 and 2. Chemical shift...