Synthesis of novel 1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) derivatives for chemoselective attachment to unprotected polyfunctionalized compounds

A convenient synthesis of novel bifunctional poly(amino carboxylate) chelating agents allowing chemoselective attachment to highly functionalized biomolecules is described. Based on the well known chelator 1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid (DOTA), we synthesized novel bifunctional chelating agents bearing additional functional groups by alkylating 1,4,7,10-tetraazacyclododecane (cyclen) with one equivalent of para-functionalized alkyl 2-bromophenyl-acetate and three equivalents of tert-butyl 2-bromoacetate. The resulting compounds, which contain an additional carbonyl or alkyne functionality, allow site specific labeling of appropriately functionalized unprotected biomolecules in a rapid manner via click reactions. This was demonstrated by the attachment of our new DOTA derivatives to the somatostatin analogue Tyr3-octreotate by chemoselective oxime ligation and CuI-catalyzed azide-alkyne cycloaddition. Initial biodistribution studies in mice with the radiometalated compound demonstrated the applicability of the described DOTA conjugation.     

A Semi Rigid Novel Hydroxamate AMPED-Based Ligand for 89Zr PET Imaging

In this work, we designed, developed, characterized, and investigated a new chelator and its bifunctional derivative for ⁸⁹Zr labeling and PET-imaging. In a preliminary study, we synthesized two hexadentate chelators named AAZTHAS and AAZTHAG, based on the seven-membered heterocycle AMPED (6-amino-6-methylperhydro-1,4-diazepine) with the aim to increase the rigidity of the ⁸⁹Zr complex by using N-methyl-N-(hydroxy)succinamide or N-methyl-N-(hydroxy)glutaramide pendant arms attached to the cyclic structure. N-methylhydroxamate groups are the donor groups chosen to efficiently coordinate ⁸⁹Zr. After in vitro stability tests, we selected the chelator with longer arms, AAZTHAG, as the best complexing agent for ⁸⁹Zr presenting a stability of 86.4 ± 5.5% in human serum (HS) for at least 72 h. Small animal PET/CT static scans acquired at different time points (up to 24 h) and ex vivo organ distribution studies were then carried out in healthy nude mice (n = 3) to investigate the stability and biodistribution in vivo of this new ⁸⁹Zr-based complex. High stability in vivo, with low accumulation of free ⁸⁹Zr in bones and kidneys, was measured. Furthermore, an activated ester functionalized version of AAZTHAG was synthesized to allow the conjugation with biomolecules such as antibodies. The bifunctional chelator was then conjugated to the human anti-HER2 monoclonal antibody Trastuzumab (Tz) as a proof of principle test of conjugation to biologically active molecules. The final ⁸⁹Zr labeled compound was characterized via radio-HPLC and SDS-PAGE followed by autoradiography, and its stability in different solutions was assessed for at least 4 days.     

两位置交换问题魔角旋转核磁共振时域信号的准确解

已知两位置交换分子运动速率对于静态¹³CNMR谱的影响是由一简单代数关系决定,它已成为分析固体中分子运动的常规方法.慢速的魔角旋转可以保留边带,所产生的边带型原则上也可用来分析分子运动,只是缺乏象静态谱那样的简单的关系,以至于在实际应用上是不可行的.本文给出作者所发现的存在分子运动时魔角旋转核磁共振自由诱导衰减信号的解析表达式的理论推导,提供分析固体分子运动的理论谱计算公式.我们选择二甲矾(dimethylsulfone)作为模型化合物,记录其不同温度下¹³CNMR谱,又计算了两个甲基做两位置交换运动的理论谱.理论谱与实验谱定性一致.定量上,边带强度存在一些差别,但边带宽度符合很好.通过理论谱与实验谱的比较,得到交换速率与温度的对应关系.虽然本文限于化学位移各向异性相互作用两位置交换问题,但容易推广到偶极作用多位置交换问题.     

Determination of Multiple φ-Torsion Angles in Proteins by Selective and Extensive C Labeling and Two-Dimensional Solid-State NMR

We describe an approach to efficiently determine the backbone conformation of solid proteins that utilizes selective and extensive ¹³C labeling in conjunction with two-dimensional magic-angle-spinning NMR. The selective ¹³C labeling approach aims to reduce line broadening and other multispin complications encountered in solid-state NMR of uniformly labeled proteins while still enhancing the sensitivity of NMR spectra. It is achieved by using specifically labeled glucose or glycerol as the sole carbon source in the protein expression medium. For amino acids synthesized in the linear part of the biosynthetic pathways, [1-¹³C]glucose preferentially labels the ends of the side chains, while [2-¹³C]glycerol labels the C^α of these residues. Amino acids produced from the citric-acid cycle are labeled in a more complex manner. Information on the secondary structure of such a labeled protein was obtained by measuring multiple backbone torsion angles φ simultaneously, using an isotropic–anisotropic 2D correlation technique, the HNCH experiment. Initial experiments for resonance assignment of a selectively ¹³C labeled protein were performed using ¹⁵N–¹³C 2D correlation spectroscopy. From the time dependence of the ¹⁵N–¹³C dipolar coherence transfer, both intraresidue and interresidue connectivities can be observed, thus yielding partial sequential assignment. We demonstrate the selective ¹³C labeling and these 2D NMR experiments on a 8.5-kDa model protein, ubiquitin. This isotope-edited NMR approach is expected to facilitate the structure determination of proteins in the solid state.     

A labeling scheme for young tableaux spanning representations of permutation group S(N)

A structure‐dependent labeling scheme for the Standard Young Tableaux spanning the representations of the permutation group is outlined in the present work. This scheme is used to generate the representations of a select class of permutations such as dense cycles and general transpositions of the group using minimal storage requirements. Two distinct approaches are outlined for generating the tableaux in the present labeling scheme. Detailed application has been made to two‐column Young diagram representations that are extremely useful in electron correlation studies in molecules. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 185–190, 2000     

Proximity‐preserving labeling schemes

This article considers informative labeling schemes for graphs. Specifically, the question introduced is whether it is possible to label the vertices of a graph with short labels in such a way that the distance between any two vertices can be inferred from inspecting their labels. A labeling scheme enjoying this property is termed a proximity‐preserving labeling scheme. It is shown that, for the class of n‐vertex weighted trees with M‐bit edge weights, there exists such a proximity‐preserving labeling scheme using O(M log n + log²n) bit labels. For the family of all n‐vertex unweighted graphs, a labeling scheme is proposed that using O(log² n · κ · n^1/κ) bit labels can provide approximate estimates to the distance, which are accurate up to a factor of In particular, using O(log³n) bit labels, the scheme can provide estimates accurate up to a factor of $\sqrt{2 \log n}$. (For weighted graphs, one of the log n factors in the label size is replaced by a factor logarithmic in the network's diameter.) © 2000 John Wiley & Sons, Inc. J Graph Theory 33: 167–176, 2000     

Models for the Carbonyl–ene Cyclization Reaction: Open and Closed Transition States

Different cyclization products are formed with different Lewis acids in the ene cyclization of 5-hexenals (see scheme on the right; a: methylaluminum bisphenoxide, b: Me₂AlCl, c: Sc(OSO₂CF₃)₃). This is not surprising, but it is gratifying that these result can be rationalized with an internally consistent model.     

Mevalonate-Independent Biosynthesis of Terpenoid Volatiles in Plants: Induced and Constitutive Emission of Volatiles

Terpenoids from flower and leaf volatiles are predominantly synthesized along the mevalonate-independent pathway, as shown by administration of [D₂]deoxy-D -xylulose and [D₅]mevalolactone. The parallel use of two pathways for the biosynthesis of the sesquiterpenoid-derived 4,8-dimethylnona-1,3,7-triene (DMNT, see picture) may be important to ensure the synthesis of the volatile alarm codes of plants.     

Reverse versus Normal Prenyl Transferases in Paraherquamide Biosynthesis Exhibit Distinct Facial Selectivities

Both a face-selective and a non-face-selective mode of formation of quaternary centers of isoprene-derived structural moieties of the natural alkaloid paraherquamide A ( 1 ) have been discovered by feeding experiments on Penicillium fellutanum with [U-¹³C₆]-glucose and [¹³C₂]-acetate. The labeling patterns suggest that the methyl groups (C22, C23) are introduced in a non-face-selective manner by a reverse prenyl transferase. The C₅ unit comprising the dioxepin moiety retains stereochemical integrity indicative of a single, face-selective addition of the phenolic group to the dimethylallyl group.