beta-Peptides have attracted considerable attention by virtue of their ability to populate helical secondary structures in methanol, even in the absence of stabilizing tertiary interactions. Recent efforts in beta-peptide design have produced few beta3-peptides that form stable 14-helices in water; those that do require stabilizing intramolecular salt bridges on two of three helical faces and therefore possess limited utility as tools in biological research. Here we show that favorable interactions with the 14-helix macrodipole significantly stabilize the 14-helix in water, alleviating the need for multiple salt bridges on two of three helical faces. We also report the previously unrecognized stabilization of 14-helix structure by gamma-branched beta3-amino acids. The most structured molecules we describe are highly heterogeneous at the primary sequence level, containing seven different beta3-amino acids within an 11-residue sequence. These results represent the essential first step toward the design of well-folded 14-helices that explore the interactions between beta3-peptides and biological macromolecules in vitro and in vivo.

Misregulation of protein translation plays a critical role in human cancer pathogenesis at many levels. Silvestrol, a cyclopenta[b]benzofuran natural product, blocks translation at the initiation step by interfering with assembly of the eIF4F translation complex. Silvestrol has a complex chemical structure whose functional group requirements have not been systematically investigated. Moreover, silvestrol has limited development potential due to poor druglike properties. Herein, we sought to develop a practical synthesis of key intermediates of silvestrol and explore structure-activity relationships around the C6 position. The ability of silvestrol and analogues to selectively inhibit the translation of proteins with high requirement on the translation-initiation machinery (i.e., complex 5'-untranslated region UTR) relative to simple 5'UTR was determined by a cellular reporter assay. Simplified analogues of silvestrol such as compounds 74 and 76 were shown to have similar cytotoxic potency and better ADME characteristics relative to those of silvestrol.

Microporous manganese oxides have been prepared by nonaqueous sol-gel reactions involving tetrabutylammonium (TBA) or tetraethylammonium (TEA) permanganate and methanol in the presence of alkali cation dopants. Layered birnessite-type materials were obtained for Na + and K + dopants in a 0.5:1 reactant ratio with manganese. Na-birnessite was isolated in hydrated and dehydrated forms (7 vs 5.6 Å interlayer spacing) whereas only the hydrated K-birnessite was observed. Cryptomelane was generated with a K:Mn ratio of 0.25:1. Spinel manganese oxides were formed with Li + dopants using 0.5:1 and 0.75:1 Li:Mn ratios. The materials were characterized by powder X-ray diffraction (XRD), elemental analyses, Mn oxidation state determination, thermogravimetric analysis, and scanning electron microscopy. Thin films of manganese oxides were prepared by spin coating TEAMnO 4 -derived sols onto glass slides. Unlike the bulk gel syntheses, only layered birnessite phases were obtained for thin films with Li + , Na + , and K + dopants. Aerogels of K-birnessite and cryptomelane were prepared by supercritical fluid extraction of bulk gels with carbon dioxide. Surface areas were increased over the conventional sol-gel workup, but overall the values were not exceptional in these preliminary experiments.

The virulence and broad host range of Fusarium graminearum is associated with its ability to secrete an arsenal of phytotoxic secondary metabolites, including the regulated mycotoxins belonging to the deoxynivalenol family. The TRI genes responsible for the biosynthesis of deoxynivalenol and related compounds are usually expressed during fungal infection. However, the F. graminearum genome harbors an array of unexplored biosynthetic gene clusters that are also co-induced with the TRI genes, including the nonribosomal peptide synthetase 8 (NRPS8) gene cluster. Here, we identify two bicyclic lipopeptides, gramillin A (1) and B (2), as the biosynthetic end products of NRPS8. Structural elucidation by high-resolution LC-MS and NMR, including 1 H-15 N-13 C HNCO and HNCA on isotopically enriched compounds, revealed that the gramillins possess a fused bicyclic structure with ring closure of the main peptide macrocycle occurring via an anhydride bond. Through targeted gene disruption, we characterized the GRA1 biosynthetic gene and its transcription factor GRA2 in the NRPS8 gene cluster. Further, we show that the gramillins are produced in planta on maize silks, promoting fungal virulence on maize but have no discernible effect on wheat head infection. Leaf infiltration of the gramillins induces cell death in maize, but not in wheat. Our results show that F. graminearum deploys the gramillins as a virulence agent in maize, but not in wheat, thus displaying host-specific adaptation.

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A convergent two-step process is described for the synthesis of ene-1,5-diols that provides for union of two carbonyl electrophiles via a formal pentenyl dianion equivalent.

[reaction: see text] A convergent route to a C1-C15 fragment precursor for erythromycin-based macrolide antibiotics is presented. These studies define a role for tethered alkoxides in the control of site-selective carbon-carbon bond formation in titanium alkoxide-mediated coupling reactions of internal alkynes and chiral aldehydes.

Background: Among the regulated mycotoxins that contaminate global food supplies, ochratoxin A is particularly harmful as a nephrotoxin and suspected carcinogen. Objective: To support global measurement comparability, certified calibration solutions for ochratoxin A and [13C6]-ochratoxin A (OTAN-1 and OTAL-1, respectively) as well as a mycotoxin-contaminated rye flour certified reference material (CRM) known as MYCO-1 were developed. Methods: Quantitative proton NMR was used along with maleic acid as an external standard traceable to the Système international (SI) to measure the concentration of ochratoxin A and [13C6]-ochratoxin A for the calibration solutions. OTAN-1 and OTAL-1 were then used as a pair in double isotope dilution MS to certify the mass fraction of ochratoxin A in MYCO-1. The natural ochratoxin A CRM served as the primary standard for traceable quantitation, while the synthetic [13C6]-ochratoxin A CRM served as the internal standard. Results: The certified mass fraction of ochratoxin A or [13C6]-ochratoxin A in the two mycotoxin calibration solution standards was established to be 11.03 ± 0.32 µg/g (k = 2) for OTAN-1 and 4.89 ± 0.18 µg/g (k = 2) for OTAL-1. The mass fraction of ochratoxin A in the rye flour standard MYCO-1 was certified at 4.05 ± 0.88 µg/kg (k = 2). Conclusions: These CRMs will support regulatory testing as they can be used in the method development, validation, calibration, and QC analysis of ochratoxin A. Highlights: This report highlights the methods used to certify OTAN-1, OTAL-1, and MYCO-1 as well as the challenges associated with producing such materials, which can be applied to a wide variety of other CRMs.