Lankacidins

O- Acetyl-8- O-acyl-lankacidin C Deacylation Corresponding 8-O-Acyllankaddins Streptomyces rochet... 

Lankacldin A Lankacldinol A Lankacidin C Streptomyces rochei, Aspergillus niger Aspergillys sojae Trametes sanguinea... 

In their synthesis of lankacidin antibiotics, an insertion reaction of an azidoformate-derived acyinitrene on the electron-rich dihydrofuran 290 to introduce the sterically hindered C-3 amino appendage in the macrocyclic framework. The oxazoline formation is totally stereospecific with the... 

Sedecamycin is an example with a 17-membered ring that belongs to the lankacidin group of antibiotics. It is a neutral compound since, unlike other macro-lides containing amino sugars, sedecamycin does not contain amino sugar moieties (93). 

Sedecamycin is a macrolide primarily used for treating swine dysentery. As with most macrolides, sedecamycin is extensively metabolized in swine 20 metabolites have been detected, the major ones being lankacidin C, lankacidinol, and lankacidinol A (106). 

Scheme 13 KCN-promoted methanolysis of P-lactam 30 en route to lankacidin C synthesis...

The implementation of this methodology for a synthesis of advanced macro-cyclic precursors of antitumor antibiotics lankacidins, which posses a carbocyclic structure, has been reported by Thomas [77]. In such a route, Scheme 13, one of the key steps is the ring opening of the (3-lactam nucleus in 30 by methanol, assisted by KCN, to give the corresponding (3-amino ester intermediate 31. The latter, upon cyclization and protecting group manipulation, renders 32, which on subsequent elaboration affords lankacidin C. 

Lewis acids can also be exploited for the cleavage of isopropylidene derivatives. One of the mildest examples comes from a synthesis of Lankacidin in which cleavage of an isopropylidene acetal without harm to a p-methoxybenzyl ether was effected with copper(Il) chloride dihydrate in methanol at reflux [Scheme 3.11].13 Alternatively, zinc(II) nitrate hexahydrate in acetonitrile at 50 DC can be used in which case even a primary tert-butyldimethylsilyl ether survives [Scheme 3.12].14 During a synthesis of Quinocarin, Katoh and co-workerscleaved an isopropylidene group using iron(IIT) chloride adsorbed onto silica gel [Scheme 3.13]. 

In the final step of a synthesis of the antitumour antibiotic Lankacidin C, Kende and co-workers55 were faced with the difficult deprotection of a bis-TBS ether [Scheme 4.35] without cleavage of the delicate pyrandione ring. Desilylation failed with all variants of fluoride or HF, but it was finally achieved using aqueous formic acid at 20 °C for 3 h to produce Lankacidin C in 82% yield. 

Various examples of use of alkenyltin/vinyl iodide couplings in natural-product synthesis have been provided Evans and Black [33] have obtained the macrolide insecticide (+)-A83 453A [(+)-lepicidin A] (Scheme 4-7), Burke et al. the ionophore antibiotic X-14547A [34] (Scheme 4-8), Kende et al. [35] lankacidin C (Scheme 4-9), while Han and Wiemer [36] have used the combination alkenyltin/vinyl triflate in the total synthesis of (+)-jatrophone. 

O-Acetyl-8-O-acyf-lankacidin C Deacytation Corresponding 8-O-Acyllankaddins Streptomyces rodtel... 

Lankacidin A Lankacidinol A Lankaddin C Streptomyces rochel, Aspergillus niger As rgillys sojae Trametes sartguirtea... 

Mata, E.G., and Thomas, E.J., Development of a synthesis of lankacidins. An investigation into 17-membered ring formation, J. Chem. Soc., Perkin Trans. 1, 785, 1995. 

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