Guapsidial A and Guadials B and C: Three New Meroterpenoids with Unusual Skeletons from the Leaves of Psidium guajava

A novel sesquiterpene‐based Psidium meroterpenoid, possessing an unusual coupling pattern, and two new monoterpene‐based meroterpenoids with unprecedented skeletons were isolated from the leaves of Psidium guajava. Their structures and absolute configurations were elucidated by spectroscopic, X‐ray diffraction, and computational methods. The plausible biosynthetic pathway of these meroterpenoids as well as their cytotoxicities toward HepG2 and HepG2/ADM cells were also discussed.     

Asymmetric Total Synthesis of ent‐Pyripyropene A

An asymmetric total synthesis of ent‐pyripyropene A was achieved by a convergent synthetic route. We used our originally developed Ti^III‐catalyzed radical cyclization to construct an AB‐ring portion that consisted of a trans‐decalin skeleton with five contiguous stereogenic centers. The coupling between the AB‐ring and the DE‐ring portions, and a subsequent C‐ring cyclization, led to the total synthesis of ent‐pyripyropene A. An evaluation of the insecticidal activity of ent‐pyripyropene A against two aphid species revealed that ent‐pyripyropene A was 35–175 times less active than naturally occurring pyripyropene A. This result indicated that the biological target of pyripyropene A recognizes the absolute configuration of pyripyropene A.     

Diastereoselective Synthesis of Cyclopentanoids: Applications to the Construction of the ABCD Tetracyclic Core of Retigeranic Acid A

A concise and efficient approach for the construction of the tetracyclic carbon skeleton of retigeranic acid A is described. The key transformations include a novel Rh‐catalyzed [3+2] cycloaddition of enyol to afford cyclopentanoid E , bearing two contiguous quaternary stereocenters at the bridgehead positions, and an intramolecular Pauson–Khand reaction to construct the advanced tetracyclic core structure of retigeranic acid A.     

Formation of the Main Cores Present in Natural Products by Tandem Additions

A rapid route to 5,5‐ and 5,6‐ bicyclic systems is provided by an 1,3‐alkyl‐shift process mediated by a hypervalent iodine reagent on aromatics. The structures obtained contain several unsaturations with different behaviors and reactivities. Such diversity allows further elaborations for the rapid formation of compact systems present in a variety of natural products. The potential for further transformations has been demonstrated by performing a double Michael addition. This cyclization process is regio‐ and stereoselective due to the presence of a former benzylic substituent. Furthermore, an extension of this approach has been accomplished on indole derivatives.     

Designing the Molybdopterin Core through Regioselective Coupling of Building Blocks

Molybdopterin is an essential cofactor for all forms of life. The cofactor is composed of a pterin moiety appended to a dithiolene‐functionalized pyran ring, and through the dithiolene moiety it binds metal ions. Different synthetic strategies for dithiolene‐functionalized pyran precursors that have been designed and synthesized are discussed. These precursors also harbor 1,2‐diketone or osone functionality that has been condensed with 1,2‐diaminobenzene or other heterocycles resulting in several quinoxaline or pterin derivatives. Use of additives improves the regioselectivity of the complexes. The molecules have been characterized by ¹H and ¹³C NMR and IR spectroscopies, as well as by mass spectrometry. In addition, several compounds have been crystallographically characterized. The geometries of the synthesized molecules are more planar than the geometry of the cofactor found in proteins.     

Role of refractive index in sum frequency generation intensity of salt solution interfaces

Sum frequency generation spectroscopy (SFG) has been widely used to study the interfacial chemistry of aqueous salt solutions of biological or environmental importance. Most of the SFG data analysis used the same bulk refractive index for different salt concentrations despite of the variations of the refractive indices. Here we systematically investigate the influence of the refractive index on the SFG intensities at various experimental conditions. It is discovered that the SFG intensities are the most sensitive to the refractive index at solid/liquid interfaces nearby the total internal reflection geometries. At air/liquid interfaces, the effect of the refractive indices is also nonegligible. Consequently some important SFG results, such as the response of water structures to the ionic strength at the SiO₂/aqueous interfaces, are necessary to be reevaluated. These conclusions on the effect of the small variations of the refractive index are generally useful for the common practice of SFG data analysis.     

流动注射-分光光度法测定天然产物对酪氨酸酶活性的影响

建立了一种快速、灵敏且高精度的流动注射-分光光度法用于研究天然产物对酪氨酸酶活性的影响。此方法基于一定介质条件下L-3,4-二羟基苯丙氨酸(L-DOPA)在酪氨酸酶的作用下,发生氧化生成棕褐色多巴醌,其最大吸收峰位于475 nm处,而酪氨酸酶抑制剂能降低酶促反应速度,减少多巴醌形成的量,从而降低475 nm下的吸光度值,形成倒峰。在优化实验条件下,半抑制浓度的曲酸抑制酪氨酸酶活性测定相对标准偏差(n=10)为0.036%,与分光光度法和酶标仪微量法相比,精密度提高了10倍以上。咖啡酸对酪氨酸酶有较强的激活作用,对二酚酶相对激活率达到50%时的浓度(IC50)为0.170 mmol/L;薰衣草花水相提取物具有较强的抑制活性,其IC50值为0.96 mg/m L。与分光光度法及酶标仪微量法相比,流动注射-分光光度法精密度高,重复性好,适用于天然产物对酪氨酸酶活性影响的测定。     

Mass spectrometry detection of minor new meridianins from the antarctic colonial ascidians Aplidium falklandicum and Aplidium meridianum

Taking into account the broad biological activities found in the meridianin indole alkaloids isolated to date, we have re‐examined the organic extracts of an Antarctic collection of the tunicates Aplidium meridianum and A. falklandicum (Chordata: Ascidiacea) by HPLC in conjunction with a high‐resolution mass spectrometer (HPLC‐MS). A new set of analogs of meridianins A–G has been detected, and their structures are proposed on the basis of the molecular formulae identified by LC‐HRMS analysis using a C18 column with a gradient of water/acetonitrile and an LTQ‐FT‐MS Orbitrap detector. Remarkably, dimers derived from meridianin A and from meridianin B or E were also detected. Our findings provide further evidence of the broad variability within the meridianin‐like derivatives of this highly bioactive alkaloid family. Copyright © 2015 John Wiley & Sons, Ltd.     

Total Syntheses of (−)‐Huperzine Q and (+)‐Lycopladines B and C

Utilizing a late‐stage enamine bromofunctionalization strategy, the twelve‐step total synthesis of (?)‐huperzine Q was accomplished. Furthermore, the first total syntheses of (+)‐lycopladines B and C are described. An unprecedented X‐ray crystal structure of an unusual epoxyamine intermediate is also reported, and the synthetic application of this intermediate in natural product synthesis is demonstrated.