An efficient one step, retro-biomimetic procedure for the synthesis of natural products having the atisane structure is described (Scheme 2), natural products which are components of medicinal plants and possess relevant biological activity. Their structures were confirmed by chemical transformations and spectral data. The starting materials were the known ent-kaur-16-en-19-oic acid (1) and ent-trachyloban-19-oic acid (2), diterpenoids readily available from the waste of sunflower.Introduction. -Tetracyclic atisanes, beyeranes, kauranes, and pentacyclic trachylobanes represent an important group of biosynthetically closely related polycyclic diterpenes, many of which display a wide range of biological activities [1 -7]. According to the hypothesis of diterpene biogenesis [8], diterpenes belonging to the families of ent-beyerene (A), ent-kaurene (B), ent-trachylobane (C), and ent-atisene (D) might all arise from (À)-copalyl pyrophosphate E via nonclassical carbocations such as F as common intermediates (Scheme 1). This hypothesis [8] has been formulated on the basis of the known isoprene rule and, to the best of our knowledge, has not been turned down yet. Scheme 1 provides a general overview of this biogenetic scheme, and our primary intention was to perform the retro-biomimetic transformation of ent-kaurene (B) to ent-beyerene (A) or ent-atisene (D) (path B ! F ! A or D).The rearrangements of ent-kaurane-and ent-trachylobane-type diterpenes have been reported under the action of different reagents [9]. Most of the examples relate on the reactions involving the formation of the nonclassical carbocation of type F (Scheme 1). It is well-known from the work of Olah and co-workers [10] that superacids are very convenient generators of these species, and our own experience on the use of fluorosulfuric acid (¼ fluorosulfonic acid; FSO 3 H) as an efficient promoter of terpenoid cyclizations [11 -15] and rearrangements [16 -18] provided a motivation to investigate the behavior of ent-kaur-16-en-19-oic acid (1) [19] and ent-trachyloban-19-oic acid (2) under superacid treatment (Scheme 2).
A comparison of four synthetic approaches for highly photoluminescent blue-emitting Cd0.15Zn0.85S QDs using (Z)-1-(octadec-9-enyl)-3-phenylthiourea as a source of sulfur.
Methyl (2Z,6Z,10E,14E)-(3) and methyl (2E,6Z,10E,14E)-geranylfarnesoate (4) were prepared, and then individually cyclized in the presence of the superacid FSO 3 H. In the case of substrate 3, the scalaranic ester 9 (26%) and the cheilanthanic ester 10 (39%) were isolated. Under the same conditions, substrate 4 afforded a mixture of the corresponding stereoisomers 11 (25%) and 12 (63%). The observed product selectivity supports that the internal, (6Z)-configured C¼C bond in these and other biologically relevant substrates plays an essential role in the cyclization process.Introduction. -Prenols represent a large class of natural, linear isoprenoids that occur abundantly in plant kingdom. Their diversity is due to the (E/Z)-configuration of the C¼C bonds and their chain length, which may vary from two (in monoterpenols) to several thousand (in natural rubber) isoprene units [1]. Terpenols with short chain lengths (up to five isoprene units) having all their C¼C bonds in (E)-configuration are regarded as biogenetic precursors of the corresponding cyclic isoprenoids. Based on this notion, many biomimetic syntheses of cyclic terpenoids have been elaborated, which turned out to serve not only as demonstrations of the biogenetic origin of cyclic isoprenoids, but also as very efficient synthetic tool for their in vitro preparation. Superacid-catalyzed cyclization of regular-structured, short-chain terpenoids is one of the most-successful biomimetic procedures to establish a link between the cyclic compounds and their aliphatic precursors [2].Biomimetic cyclization of long-chain polyprenols has also been investigated, and successful attempts of both enzymatic [3] and superacidic [4] cyclization have been reported; but only prenols with (all-E)-configuration have been used as substrates. On the other hand, it is known that most of the natural long-chain polyprenols possess the so-called di-trans-poly-cis or tri-trans-poly-cis configuration 1 ). To the best of our knowledge, none of these compounds have been used as substrates for biomimetic cyclizations.We have shown in recent papers [5] [6] that the presence of an internal (13Z)-configured C¼C bond in the bicyclic, stereoisomeric compounds methyl (13Z,17Z)-(1) and methyl (13Z,17E)-bicyclogeranylfarnesoate (2) influences the selectivity of the
We present the study of volatile amine-based single or multi-component solvent formulations and their influence on As30Se70 chalcogenide glass solubility and dissolution mechanism. The source As30Se70 bulk glass was dissolved in various amine based solvents and solutions of quantitatively dissolved bulk glass were used for thin films deposition by spincoating technique. The methanoln-propylamine solvent mixture proved to be suitable for preparation of thin films in specular optical quality, low surface roughness and targeted composition. The post-deposition thermal treatment has high impact on thickness, optical properties and structure of studied thin films. The content of organic residuals was also significantly reduced.
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