Six novel chromanone acids (1-6) were isolated from the bark of Calophyllum brasiliense Cambess. Their structures were elucidated on the basis of 1D and 2D NMR experiments, as well as mass spectrometry. All compounds showed moderate to strong antibacterial activity against Bacillus cereus and Staphylococcus epidermidis, with 1 and 2 being most active. None of the compounds were cytotoxic against KB, Jurkat T, and myosarcoma cancer cells up to 20 microg/mL.

Combinatorial diversity in hypervariable β‐hairpin loops is exploited by the immune system to select binding sites on antibodies for a wide variety of different protein antigens. In a first step towards mimicking this strategy in vitro, for the selection of novel protein ligands, an approach is described here for the parallel synthesis of small libraries of conformationally defined β‐hairpin protein epitope mimetics. Starting from a protruding hairpin loop in platelet‐derived growth factor B (PDGF‐B), 8 and 12 residues were first transplanted from the protein to a D‐Pro‐L‐Pro template, to afford the cyclic peptide‐loop mimetics 1 and 2, respectively. NMR and MD studies in aqueous solution show that both mimetics populate conformations which closely mimic the β‐hairpin in the crystal structure of the native protein (Fig. 5). Based on 1 as a scaffold, a library of 24 mimetics was synthesized in which the four residues at the tip of the loop (VRKK) were held constant, and flanking residues at positions 1, 2, 7, and 8 in the hairpin were varied (Fig. 7). The library was prepared by parallel synthesis in a two‐stage solid‐phase assembly/solution‐phase cyclization process. The products were analyzed by MS, NMR, and CD. 2D‐NOESY revealed for most library members characteristic long‐range NOEs that show that the hairpin conformation is stably maintained. The results suggest that this approach may be useful for the synthesis of much larger libraries of peptide and protein mimetics based on a β‐hairpin scaffold.

Template-assembled proteins (TASPs) comprising 4 peptide blocks, each of either the natural melittin sequence (melittin-TASP) or of a truncated melittin sequence (amino acids 6-26, melittin,_,,-TASP), C-terminally linked to a (linear or cyclic) 10-amino acid temp1at.e were synthesized and characterized, structurally by CD, by fluorescence spectroscopy, and by monolayer experiments, and functionally, by electrical conductance measurements on planar bilayers and release experiments on dye-loaded vesicles. Melittin-TASP and the truncated analogue preferentially adopt a-helical structures in methanol (56% and 52%, respectively) as in lipid membranes. Unlike in methanol, the melittin-TASP self-aggregates in water. On an air-water interface, the differently sized molecules can be self-assembled and compressed to a compact structure with a molecular area of around 600 A ' , compatible with a 4-helix bundle preferentially oriented perpendicular to the interface. The proteins reveal a strong affinity for lipid membranes. A partition coefficient of 1.5 X lo9 M" was evaluated from changes of the Trp fluorescence spectra of the TASP in water and in the lipid bilayer. In planar lipid bilayers, TASP molecules are able to form defined ion channels, exhibiting a small single-channel conductance of 7 pS (in 1 M NaC1). With increasing protein concentration in the lipid bilayer, additional, larger conductance states of up to 1 nS were observed. These states are likely to be formed by aggregated TASP structures as inferred from a strongly voltagedependent channet activity OR membranes of large area. In this respect, melittin-TASP reveals channel features of the native peptide, but with a considerably lower variation in the size of the channel states. Compared to the free peptide, template-assembled melittin has a much higher membrane activity: it is about 1 0 0 times more effective in channel formation and 20 times more effective in releasing dye molecules from lipid vesicles. This demonstrates that the lytic properties are not solely related to channel formation. Abbreviations: 6-CF, 6-carboxyfluorescein; BLM, black lipid membranes; Boc. tert-butyloxycarbonyl; BOP, benzotriazol-I-yl-oxybis(dimethy1amino)phosphonium hexafluorophosphate; DCM, dichloromethane; DIC, diisopropylcarbodiimide; DIPEA, N-diisopropylethylamine; DMF, dimethylformarnide; DMS, dimethylsulfide; DOPC, 1,2-dioleoyl-snglycero-3-phosphocholine; DOPE, 1,2-dioleoyl-sn-glycer0-3-phosphoethanolamine; DTPC, 1,2-ditetradecyl-sn-glycero-3-phosphocholine; EDT, ethanedithiole; Fmoc, 9-fluorenylmethyloxycarbonyl; HOBt, 1-hydroxybenzotriazole; L:P, lipid to protein molar ratio; MBHA, methylbenzhydrylamine; Mob, 4-methoxybenzyl; Mtr, 4-methoxy-2,3,6-trimethylbenzenesulfonyl; POPC, I-palmitoyl-2-0leoyl-sn-glycero-3-phosphocholine; RP-HPLC, reverse-phase high-performance liquid chromatography; SUV, LUV, small, large unilamellar vesicle(s); TASP, template-assembled synthetic protein; tBu, tert-butyl ether; TFA, trifluoroacetic acid; TFMSA, trifluoromethanesulfonic acid; T...

The use of quantitative carbon nuclear magnetic resonance spectroscopy ((13)C NMR) for the determination of resin loadings has been investigated. Magic angle spinning (MAS) NMR spectra have been obtained for solvent-swollen resins on a conventional 7 mm CP/MAS probe using the two pulse phase modulation (TPPM) proton decoupling sequence. Loadings of resin-bound organic compounds were evaluated via addition of tetrakis(trimethylsilyl)silane as reference or using the carbon resonances of the polymeric resin material as an internal standard. Results for several functionalized Wang and trityl resins are consistent with those obtained using well-established analytical methods. The (13)C NMR method has interesting applications in the field of solid-phase organic synthesis (SPOS), since no functional group acting as a support for the attachment of a quantifiable chromophore must be available in the material of interest.