Alkaloids semi-synthesis

Opium is a cmde exudate obtained from the opium poppy Papaver somniferum, and it provides several medicinally useful alkaloids. One of these is codeine, which is widely used as a moderate analgesic. Opium contains only relatively small amounts of codeine (1-2%), however, and most of the codeine for dmg use is obtained by semi-synthesis from morphine, which is the major component (12-20%) in opium. Conversion of morphine into... 

The tubulin-binding properties of (-)-rhazinilam were discovered through screening of a number of Malaysian plant extracts [60]. Natural (-)-rhazinilam induces tubulin spiralization, inhibiting tubulin assembly in the same way as vinblastine-like alkaloids, and protects microtubules from cold disassembly such as with paclitaxel [67]. This effect has never been observed with other microtubule poisons. For this reason, and despite the in vivo inactivity of (-)-rhazinilam [67], a number of analogues have been prepared by semi-synthesis and total synthesis (see Sections 3.1.3. and 3.2.3.) in order to improve the pharmacological properties of this molecule. 

In this area some interest has lain firstly in the semi-synthesis of alkaloids from certain natural intermediates and secondly in functional group transformations in structural/property studies. 

Petroski RJ, Yates SG, Wdsleder D, Powell EG (1989) Isolation, semi-synthesis, and NMR spectral studies of lohne alkaloids. J Nat Prod 52 810-817 Porter JK (1995) Analysis of endophytic toxins fescue and other grasses toxic to livestock. J Anim Sci 73 871-880... 

Ephedrine A natural or semi-synthetic alkaloid that is used as a decongestant and precursor in methamphela-mine synthesis. 

The pronounced pharmacological activity associated with the tropine and scopine skeletons prompted the synthesis of a number of semi-synthetic derivatives of the solanaceous alkaloids in which various other acids were substituted for tropic acid [390]. Anticholinergic activity was evident in many of these synthetic atropine-like molecules, but only two, benztropin (Cogentin, Cobrentin, 7) and ethylbenzatropin (Ponalide, 8), have found clinical use in Parkinsonism. Neither the latter nor tigloidine (9), originally isolated from... 

The iV-oxide of indicine (100) does disply anti-tumor activity with less toxic effects than related pyrrolizidine alkaloids it has recently been tested on humans 176). Some semi-synthetic quaternary pyrrolizidine derivatives block neuromuscular transmissions, and their synthesis and biological activities have recently been reviewed 19, 261). 

A diterpene alkaloid, initially isolated from the bark of the pacific yew Taxus brevifolia, has 11 chiral centers so the number of possible diastereoisomers exceeds 2000. An important chemotherapeutic agent. Lack of adequate supply from natural sources and chirality of the molecule were the reasons for the development of a semi-synthetic conversion from baccat-ins, which are relatively abundant in other yew species whereas full synthesis is multistep and costly [55,56],... 

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