Steroids semi-synthesis

Semi-synthesis of steroids has been a rich field for the derivation of a whole range of structures at a time when total synthesis was unknown and although subsequently for certain compounds notably estrone remarkable developments have led to total synthesis, the use of natural intermediates has proved a major contribution. In this area, work initiated on semi-synthetic transformations of plant... 

The preceding information is summarised as follows. Table 3 Semi-Synthesis of Steroids... 

Among the worldwide total of 30000 known natural products, about 80% stems from plant resources. The number of known chemical structures of plant secondary metabolites is four times the number of known microbial secondary metabolites. Plant secondary metabolites are widely used as valuable medicines (such as paclitaxel, vinblastine, camptothecin, ginsenosides, and artemisinin), food additives, flavors, spices (such as rose oil, vanillin), pigments (such as Sin red and anthocyanins), cosmetics (such as aloe polysaccharides), and bio-pesticides (such as pyrethrins). Currently, a quarter of all prescribed pharmaceuticals compounds in industrialized countries are directly or indirectly derived from plants, or via semi-synthesis. Furthermore, 11% of the 252 drugs considered as basic and essential by the WHO are exclusively derived from plants. According to their biosynthetic pathways, secondary metabolites are usually classified into three large molecule families phenolics, terpenes, and steroids. Some known plant-derived pharmaceuticals are shown in Table 6.1. 

Sucrow provided one of the few examples for the use of an Eschenmoser-Claisen rearrangement involving simple diastereoselection in natural product synthesis (Scheme 7.30) [72, 73]. In a semi-synthesis of sigmastatrienol, the syn isomer 88 was preferentially formed as a consequence of the (Z)-configuration of allylic alcohol 87. Subsequent reduction to the tertiary amine followed by Cope elimination completed the installation of the steroid s side chain [74]. 

GlycoUpids, Synthesis of Imaging Techniqnes Lipids Labeling Techniqnes Lipids Lipidomics Lipids, Semi-synthetic Steroid and Triterpene Biosynthesis PHYSICAL PROPERTIES PHASE BEHAVIOR AND PHASE TRANSITIONS... 

Girgenti E, Ricoux R, Mahy JP (2004) Desi and synthesis of a Mn(III)-porphyrin steroid conjugate used as a new cleavable affinity label on the road to semi-synthetic catalytic antibodies. Tetrahedron 60 10049-10058... 

The synthesis of 1,2,3-selenadiazoles by the action of selenium dioxide on semi-carbazones, and their pyrolysis to the corresponding acetylenes (see Vol. 2, p. 720 Vol. 3, p. 673) has been applied to several examples incorporating steroid, phenanthrenyl, fluorenyl, and naphthyl residues. The method may prove useful as a route to pharmacologically active 17-ethynyl-steroids. A large number of aryl-1,2,3-selenadiazoles as well as the three isomeric 4-[(2-, 3-, and 4-)pyridyl]-... 

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