Cytochalasan intermediate

The heterocycle 43 was needed as an intermediate in a cytochalasan synthesis.10 Disconnection of the 1,3-diCO relationship between the two ketones reveals the amide 44 that is the acetoacetyl derivative of phenylalanine ethyl ester 45. 

Finally, a thia Diels-Alder reaction representing a less common cycloaddition type in natural product synthesis shall be discussed. Thus, Vedejs et al. have included such a cycloaddition into an elegant strategy aimed at the synthesis of macrocyclic [ll]-cytochalasans such as zygosporin E 7-76 [536-538]. Thus, release of the thioaldehyde 7-73 from its phenacyl sulfide precursor in the presence of the silyloxydiene 7-74 yielded 7-75 as 2 1 mixture with its C20 epimer. Fortunately, equilibration of this mixture raised the ratio up to 10 1. Several subsequent steps yielded the tetracyclic intermediate 7-77 cleavage of its thioether moiety then liberated the 11-membered macrocycle present e.g. in zygosporin E 7-76 (Fig. 7-16). 

Heterocyclic compound (24), an intermediate in a cytochalasan synthesis can be made from (25) by a 1.3-dicarbonyl route. Amide (25) is an acetoacetyi derivative of the naturally occurring artf.no acid phenylalanine (26) so this is a... 

It is evident that the final validity of this general biogenetic scheme requires additional experimental data, e.g., incorporation of tryptophan into the chaetoglobosins and cytochalasin G, isolation of intermediates of the biogenetic sequence, and discovery of new cytochalasans, possibly with the as yet unknown basic skeletons and structural elements derived from other natural amino acids. 

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