Myrmicarin

If, however, compound 390 is treated with a stronger acid (TFA), it undergoes diastereoselective dimerization reduction of the initial reaction product gives 391 (Scheme 113). It is suggested that in vivo dimerization of myrmicarin 215B may provide the key to the biosynthesis of the more complex myrmicarins such as M430 <2006T5287>. 

The decahydrocyclazine skeleton is also found in the alkaloid 395, currently known only by the designation 261C. This compound bears a passing resemblance to some of the myrmicarins (Section 16.6.5.2), but occurs in the skin of a totally different animal species, namely poisonous frogs of the genus Mantella <2003H(59)745>. 

Often, in the synthesis of natural products containing the indolizidine substructure, it is necessary to modify a preformed indolizidine ring. This is the case in the synthesis of (+)-myrmicarin 217 191 where the key step is the closure of the third ring through an electrophilic substitution on the pyrrole nucleus (Scheme 45) <2000JOC2824>. 

Scheme 4 Total synthesis of (-)-myrmicarins 237A and 237B...

Recently, Settambolo et al. [194] reported a formal synthesis of (S)-myrmi-carin 217 (206) using a sequence of reactions slightly modified from the one described in Scheme 4. Indeed, rather than to cyclize directly the diester (S)-207, the latter was first transformed into the aldehyde 219 (Scheme 7) that was further intramolecularly cyclodehydrated into ester 220. The latter can be converted into (S)-myrmicarin 217 (206) via the alcohol (S)-209 as described previously by Sayah et al. [192] (see Scheme 5). 

Angew. Chem. Int. Ed. Engl. 44, 3668-3688, 2005 Kent, M. and Tepe, J.J., One-pot Friedel-Crafts/ Robinson-Gabriel synthesis of oxazoles using oxazolone templates, J. Org. Chem. 70, 4211 213, 2005 Movassaghi, M. and Ondrus, A.E., Enantioselective total synthesis of tricyclic myrmicarin alkaloids, Org. Lett. 7, 4423 426, 2005 Paizs, C., Katona, A., and Retey, J., The interaction of heteroaryl-acrylates and alanines with phenylalanine ammonia-lyase form parsley. Chemistry 12, 2739-2744, 2006. Cuprous ions have been observed to promote a Friedel-Crafts acylation reaction (Kozikowski, A.P. and Ames, A., Copper(l) promoted acylation reactions. A transition metal-mediated version of the Friedel-Crafts reaction, J. Am. Chem. Soc. 102, 860-862, 1980). 

Two new 3,5-disubstituted indolizidines, (-)-myrmicarin 237A and (+)-myrmicarin 237B, Fig. (7), were isolated as the major components of the poison gland secretion of the afiican ant Myrmicaria eumenoides [22]. NMR data analysis ( H, COSY, COLOC and... 

Figure 8 Myrmicarin 237A (13) and 237B (14), which were identified using (13C,13C)-2D-INADEQUATE.50...

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