Evolution of dithiane-based strategies for the construction of architecturally complex natural products

Umpolung-based strategies play a significant role in organic synthesis. Particularly important are 1,3-dithiane linchpins, which serve as convenient acyl anion equivalents. The general synthetic accessibility and impressive reactivity of 1,3-dithianes have thus led to widespread application. Since the late 1970s, dithianes have featured prominently in our program directed toward the synthesis of complex natural and unnatural products, both for effective union of advanced fragments and for multicomponent linchpin couplings. In this Account, we present the evolution of dithiane chemistry in our laboratory.     

Impact of epimerization domains on the intermodular transfer of enzyme-bound intermediates in nonribosomal peptide synthesis

Assembly of bioactive natural compounds through the action of nonribosomal peptide synthetases (NRPSs) relies on the specific interplay of modules and domains along these multiple mega-enzymes. As the C termini of several bacterial NRPSs often harbor epimerization (E) domains that generate D-amino acids, these seem to facilitate the ordered intermolecular enzymatic interaction and the directed transfer of intermediates. To elucidate this bifunctional role, E domains in recombinant bimodular proteins derived from the tyrocidine synthetase B were investigated. By utilizing sequent tryptic proteolysis and HPLC Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), we could directly interrogate and determine the formation of intermediates attached to the TycB(3)-PCP domain of wild-type TycB(2-3) and to the E domain exchange enzyme TycB(2-3)-ATCAT/E(tycA). In addition, the two proteins and a version of TycB(2-3) fused to the communication-mediating (COM) domain of TycA were applied in product formation assays with TycB(1) to corroborate E domain impact on intermodular NRPS interaction. Significant functional differences between the C-terminal aminoacyl- and peptidyl-E domains were observed in terms of in trans interaction and misinitiation. E domains originating from elongation modules (peptidyl-E domains) seem to be optimized for regulation of the progression of peptide bond formation, epimerization, and intermediate transfer to the downstream module, whereas E domains of initiation modules (aminoacyl-E domains) impair upstream condensation and cause misinitiation. The selection of E domains is therefore decisive for successful application in biocombinatorial engineering of nonribosomal peptides.     

天然胶乳积层制品的脱层研究

对天然胶乳制品积层浸渍进行了研究，介绍影响积层浸渍的因素：胶模干燥程度、胶乳中的皂类、胶膜的湿润性、凝固剂，并对其规律进行研究．提出了减少积层失败的措施。     

基于天然产物表面活性剂的研究进展

天然产物衍生的表面活性剂作为一种重要的化工原料,在洗涤、印染、造纸、纺织以及石油等行业被广泛研究和应用。就基于天然产物（糖类和疏水性化合物）的表面活性剂的合成方法进行介绍,对其溶解性、分散性、熔点、润湿性、乳化性和发泡性等物理化学特征进行详细讨论。基于天然产物的绿色表面活性剂由于具有良好的生物降解性以及温和性,成为精细化学品未来发展的主要方向之一。     

Nonribosomal peptide synthesis in Schizosaccharomyces pombe and the architectures of ferrichrome-type siderophore synthetases in fungi

A nonribosomal peptide synthetase (NRPS) in Schizosaccharomyces pombe, which possesses an unusual structure incorporating three adenylation domains, six thiolation domains and six condensation domains, has been shown to produce the cyclohexapeptide siderophore ferrichrome. One of the adenylation domains is truncated and contains a distorted key motif. Substrate-binding specificities of the remaining two domains were assigned by molecular modelling to glycine and to N-acetyl-N-hydroxy-L-ornithine. Hexapeptide siderophore synthetase genes of Magnaporthe grisea and Fusarium graminearum were both identified and analyzed with respect to substrate-binding sites, and the predicted product ferricrocin was identified in each. A comparative analysis of these synthetase systems, including those of the basidiomycete Ustilago maydis, the homobasidiomycete Omphalotus olearius and the ascomycetes Aspergillus nidulans, Aspergillus fumigatus, Fusarium graminearum, Cochliobolus heterostrophus, Neurospora crassa and Aureobasidium pullulans, revealed divergent domain compositions with respect to their number and positioning, although all produce similar products by iterative processes. A phylogenetic analysis of both NRPSs and associated L-N5-ornithine monooxygenases revealed that ferrichrome-type siderophore biosynthesis has coevolved in fungi with varying in trans interactions of NRPS domains.     

Authentic heterologous expression of the tenellin iterative polyketide synthase nonribosomal peptide synthetase requires coexpression with an enoyl reductase

The tenS gene encoding tenellin synthetase (TENS), a 4239-residue polyketide synthase nonribosomal-peptide synthetase (PKS-NRPS) from Beauveria bassiana, was expressed in Aspergillus oryzae M-2-3. This led to the production of three new compounds, identified as acyl tetramic acids, and numerous minor metabolites. Consideration of the structures of these compounds indicates that the putative C-terminal thiolester reductase (R) domain does not act as a reductase, but appears to act as a Dieckmann cyclase (DKC). Expression of tenS in the absence of a trans-acting ER component encoded by orf3 led to errors in assembly of the polyketide component, giving clues to the mode of programming of highly reducing fungal PKS. Coexpression of tenS with orf3 from the linked gene cluster led to the production of a correctly elaborated polyketide. The NRPS adenylation domain possibly shows the first identified fungal signature sequences for tyrosine selectivity.     

天然活性物美白功效的细胞生物学研究

研究天然活性物对B16黑色素细胞的增值、细胞内氨酸酶活性及黑色素形成的影响，结果表明，各活性物能不同程度地抑制细胞增殖；除入参皂苷Rb外，各活性物能降低细胞内酷氨酸酶活性，茶多酚、金银花提取物和葡萄籽提取物较其他活性物能明显减少细胞黑色素的含量，是较为理想的化妆品美白添加剂，此研究模型能快速简便地筛选美白剂。     

Parametric sensitivity analysis of complex process flowsheets using sequential modular simulation

An algorithm for parametric sensitivity analysis of complex process flowsheets has been developed for use with sequential modular simulators. The method reduces the calculational effort when several sensitivities are calculated from the same flowsheet. A study of the efficiency of these methods is presented in the context of two example problems. Computational savings of order 100 are reported relative to sensitivity analysis by the continuation (restart) method. The method presented allows direct analysis of dependent variable variations which can be used to examine the effects of model prediction error. Furthermore, the algorithm lends itself to a structural analysis to quickly identify which variables in a flowsheet yield zero sensitivities and may be eliminated a priori from the sensitivity calculation.     

Unraveling the biosynthesis of penicillenols by genome mining polyketide synthase and nonribosomal peptide synthetase gene clusters in Penicillium citrinum

Penicillenols belong to the family of tetramic acids with anticancer and antibacterial activities. Here, we report the discovery of the biosynthetic gene cluster (pnc) for penicillenol A₁ and E in Penicillium citrinum ATCC9849 by genome mining. We discover the pnc cluster based on the results of gene deletions in P. citrinum and gene cluster heterologous expression in Aspergillus nidulans. We also propose the assembly line of the polyketide synthase module in PncA with the reduction by PncB provides a highly reduce polyketide chain to be further linked with an l -threonine molecule and released from PncA to produce penicillenol E. Further formation of penicillenol A₁ requires the N-methylation of tetramic acid group by PncC. Our work deepens the understanding of the biosynthetic logic for N-methylated tetramic acids and contributes to the discovery of new penicillenols by genome mining.     

甘露醇在天然产物合成中的应用

介绍了甘露醇作为手性材料在具有重要生理活性天然产物合成中的应用概况。