Macrolactonisation

Several reaction were examined the dehydrobromination of bromoalkanes, the esterification of benzoic acid with 1-bromobutane and the macrolactonisation of [Pg.138]

Fig. 5. Incorporation of [1- C/ O2]-, [1- C, 2-2H3]acetates and 02 into colletodiol and an acyl substitution mechanism for macrolactonisation...

The synthetic strategy for obtaining avermectin B g involves preparation of the northern segment (C 28 unit) and the southern segment (C.j-C3o unit), followed by coupling of the above two segments, macrolactonisation, stereocontrolled glycosylation and adjustment of the functionality [118],... 

Brady. P.A. Bonar-Law. R.P. Rowan. S.J. Suckling, C.J. Sanders, J.K.M. Living macrolactonisation Thermodynamically-controlled cyclisation and interconversion of oligocholates. Chem. Commun. 19%. 319-320. 

As part of their investigations towards the synthesis of the cytotoxic marine natural product diazonamide A, Feldman et al. discovered a noteworthy atroposelective macrolactonisation reaction. Thus, the ring closure of the configurationally flexible model bisindole depicted in Scheme 5.29 afforded the corresponding lactone as a single isomer. The bulk of the NB0C2 group was... 

Other approaches to make macrocyclic ring systems exist as well. Smith and Ott prepared the central framework of (-)-macrolactin A by using a Mitsunobu reaction to prepare a linear precursor for the final ring closure reaction with a Stille reaction. The Mitsunobu reaction proceeded in 74% yield the Stille reaction, in contrast, took seven days and provided the desired macrocyclic intermediate 60 in 42% yield. In an inverse approach, Williams and Meyer prepared (+)-amphidinolide K by preparing a seco-acid macrolactonisation precursor via Stille reaction and then using the Mitsunobu reaction to close the ring to form 61. ... 

Fig. 1.8 Biosynthesis of erythromycin A (7) by the DEBS system, an example of a modular t5rpe I PKS. The three DEBS proteins harbour six elongating modules and a loading module. The TE domain catalyses a macrolactonisation releasing 6-dEB (13), which is further modified to yield (7)...

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