The modification of highly oxygenated forskolin as well as manoyl and epi-manoyl oxide, two less functionalized model substrates sharing the same polycyclic skeleton, via intermolecular carbon-centered radical addition to the vinyl moiety has been investigated. Highly regio- and reasonably stereoselective iodine atom transfer radical addition (ATRA) reactions were developed. Unprotected forskolin afforded an unexpected cyclic ether derivative. Protection of the 1,3-diol as an acetonide led the formation of the iodine ATRA product. Interestingly, by changing the mode of initiation of the radical process, in situ protection of the forskolin 1,3-diol moiety as a cyclic boronic ester took place during the iodine ATRA process without disruption of the radical chain process. This very mild radical-mediated in situ protection of 1,3-diol is expected to be of interest for a broad range of radical and non-radical transformations. Finally, by using our recently developed tert-butylcatechol-mediated hydroalkylation procedure, highly efficient preparation of forskolin derivatives bearing an extra ester or sulfone group was achieved.
Scalarane sesterterpenoids emerged as interesting bioactive natural products which were isolated extensively from marine sponges and shell-less mollusks. Some representatives were also reported recently from superior plants. Many scalarane sesterterpenoids displayed a wide spectrum of valuable properties, such as antifeedant, antimicrobial, antifungal, antitubercular, antitumor, anti-HIV properties, cytotoxicity and stimulation of nerve growth factor synthesis, as well as anti-inflammatory activity. Due to their important biological properties, many efforts have been undertaken towards the chemical synthesis of natural scalaranes. The main synthetic challenges are connected to their complex polycyclic framework, chiral centers and different functional groups, in particular the oxygenated functional groups at the C-12 position, which are prerequisites of the biological activity of many investigated scalaranes. The current work addresses this problem and the synthesis of 17-oxo-20-norscalaran-12α,19-O-lactone is described. It was performed via the 12α-hydroxy-ent-isocopal-13(14)-en-15-al obtained from (-)-sclareol as an accessible starting material. The tetracyclic lactone framework was built following an addition strategy, which includes the intramolecular Michael addition of a diterpenic acetoacetic ester and an intramolecular aldol condensation reaction as key synthetic steps. The structure and stereochemistry of the target compound have been proven by X-Ray diffraction method.
Abstract. This paper presents a review on kaurane diterpenes, covering various aspects of chemical and microbiological transformations of native ent-kaurenoic acid, namely, its reactions via COOH groups, double bonds and rearrangements of the carbon skeleton that lead to a wide range of natural and synthetic derivatives with potential biologic activities and can present convenient synthons for the syntheses of other native ent-kauranes. Ent-kaur-16-en-19-oic acid 1 is one of the intermediate compounds, which is involved in the biosynthesis of diverse ent-kaurane diterpenes, including gibberellins, a group of growth phyto-hormones. Therefore, it is not surprising that many ent-kauranes and their derivatives act as growth regulators in plants [25]. KeywordsThe broad spectrum of presented by the ent-kaurane diterpenes biological activities has motivated countless studies of structural modifi cations of the skeleton, aiming at obtaining the new potentially bioactive substances. These structural transformations have been achieved either chemically or microbiologically, by using microorganism cultures.
Abstract. The accumulated waste fat as production from Faraon quail breeds has been investigated for the fi rst time by using GC-MS technique, preventively converting it via methanolysis to fatty acid methyl esters. The test results, regarding the content of unsaturated fatty acids having a favorable to human body cis-confi guration (77.8%), confi rm their nutritional value and the possibility of using this fat in cosmetic, pharmaceutical and food industries.
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