SUMMARYThylakoids are the photosynthetic membranes in chloroplasts and cyanobacteria. The aqueous phase inside the thylakoid known as the thylakoid lumen plays an essential role in the photosynthetic electron transport. The presence and significance of thiol-disulfide exchange in this compartment have been recognized but remain poorly understood. All proteins found free in the thylakoid lumen and some proteins associated to the thylakoid membrane require an N-terminal targeting signal, which is removed in the lumen by a membrane-bound serine protease called thylakoidal processing peptidase (TPP). TPP is homologous to Escherichia coli type I signal peptidase (SPI) called LepB. Genetic data indicate that plastidic SPI 1 (Plsp1) is the main TPP in Arabidopsis thaliana (Arabidopsis) although biochemical evidence had been lacking. Here we demonstrate catalytic activity of bacterially produced Arabidopsis Plsp1. Recombinant Plsp1 showed processing activity against various TPP substrates at a level comparable to that of LepB. Plsp1 and LepB were also similar in the pH optima, sensitivity to arylomycin variants and a preference for the residue at À3 to the cleavage site within a substrate. Plsp1 orthologs found in angiosperms contain two unique Cys residues located in the lumen. Results of processing assays suggested that these residues were redox active and formation of a disulfide bond between them was necessary for the activity of recombinant Arabidopsis Plsp1. Furthermore, Plsp1 in Arabidopsis and pea thylakoids migrated faster under non-reducing conditions than under reducing conditions on SDS-PAGE. These results underpin the notion that Plsp1 is a redoxdependent signal peptidase in the thylakoid lumen.

Die absolute Konfiguration des Naturstoffs RP‐66453 (1) wurde durch Totalsynthese seines Atropdiastereomers und spektroskopische Studien beider Verbindungen zu aR, S, S, S, S, S bestimmt. Eine SNAr‐basierte cyclische Etherbildung und eine intramolekulare atropdiastereoselektive Suzuki‐Miyaura‐Kupplung wurden zum Aufbau des schwer zugänglichen bicyclischen A‐B‐O‐C‐Gerüsts von RP‐66453 genutzt.

Polysubstituted furan has been found as a key structural unit in many bioactive natural products and pharmaceuticals. [1] It is also a reactive species that, upon appropriate activation, can be engaged in complex chemical transformations. [2] The development of efficient furan syntheses has thus attracted chemists for decades and continues to be an active and rewarding research area. [3,4] Besides polysubstituted furans, various annulated derivatives such as benzo-, thieno-, isoxazolo-, furo-, pyridino-, pyridazino-, and indolofuran have been synthesized and their properties investigated. [5] Cyclization of acyclic precursors and derivatization of an appropriately functionalized furan ring are two main strategies used for the elaboration of polysubstituted furans. New technologies such as solid-phase synthesis [6] and multicomponent reactions [7] have recently been developed for the preparation of this heterocycle.Furoquinoline alkaloids, typical constituents of the Rutaceae and Solanaceae plant species, are the most widely distributed of quinoline alkaloids. [8] Antimicrobial, antitumor, and antiemetic activities have been attributed to both natural and synthetic analogues of these molecules. [9] While several synthetic routes to individual furoquinolines have been developed, most of them were linear and involved harsh reaction conditions. [10,11] In connection with our ongoing project aimed at using oxazoles as a starting point to reach diverse druglike heterocycles, [12] we report herein a conceptually novel multicomponent domino synthesis of furo[2,3c]quinoline 1 (Scheme 1) from readily available substrates. [13,14] Using methyl 3-(2-aminophenyl)prop-2-ynoate (2 a), heptanal (3 a), and isocyanoacetamide (4 a) as substrates, a survey of reaction conditions is summarized in Table 1. The reaction proceeded in refluxing toluene to provide the desired furoquinoline 1 a (R 1 ¼ H, R 2 ¼ CO 2 CH 3 , R 3 ¼ (CH 2 ) 5 CH 3 , NR 4 R 5 ¼ morpholinyl), albeit in low yield. Both lithium bromide [15] and camphorsulfonic acid were detrimental to the desired transformation, while ammonium chloride [16] promoted the reaction sequence efficiently, providing 1 a in 75 % yield.The scope of this novel multicomponent reaction was examined using three ortho-alkynyl anilines, [17] five aldehydes, and three isocyanoacetamides as substrates (Scheme 2). Some representative furoquinolines synthesized are shown in Scheme 3. The potential and general applicability of this novel three-component domino process is readily seen from these selected examples. Aniline derivatives bearing both electronically poor and electronically neutral acetylene units participated in the reaction. For the aldehyde substrate, aliphatic aldehydes, including sterically hindered isobutyraldehyde, and aromatic aldehydes bearing electron-donating or -withdrawing groups were suitable. Various substituted amino groups were easily incorporated by varying the isocyanoacetamide substrate. The presence of aryl bromide and ester functional groups in furoquinolines sho...