ABSTRACT
The total synthesis of the cyclic diterpene ent-tonantzitlolone (ent-1) is presented. Key steps for assembling the macrocyclic core structure of 1 are a highly selective aldol reaction and an E selective ring-closing metathesis reaction. A detailed investigation of these two steps and the final transformations towards the completion of the synthesis is disclosed.
Subject(s)
Diterpenes/chemical synthesis , Macrocyclic Compounds/chemical synthesis , Cyclization , Models, Chemical , StereoisomerismABSTRACT
[structure: see text] The enantioselective total synthesis of the N-acetylcysteamine thioester of seco-proansamitocin, a key biosynthetic intermediate of the highly potent antitumor agent ansamitocin, is described, which twice utilizes the Nagao acetate aldol reaction, as well as an indium-mediated alkynylation of a benzyl bromide followed by carboalumination. The key step is a Heck reaction between two terminal alkenes for merging the two major fragments.
Subject(s)
Cysteamine/analogs & derivatives , Maytansine/analogs & derivatives , Cysteamine/chemistry , Esters , Maytansine/chemical synthesis , Maytansine/chemistryABSTRACT
[structure: see text] The first enantioselective total synthesis of tonantzitlolone, a novel 15-membered macrocyclic diterpene, utilized a Julia olefination, a highly selective, potassium enolate-based anti-Felkin aldol reaction, and an E-selective ring-closing metathesis as key C-C bond-forming steps. The absolute configuration of tonantzitlolone is established.
Subject(s)
Diterpenes/chemical synthesis , Macrocyclic Compounds/chemical synthesis , Indicators and Reagents , Molecular Conformation , Stereoisomerism , ThermodynamicsABSTRACT
Callystatin A is a prominent member of a class of natural products which display promising growth inhibition of cancer cells in their biological profile. The challenging structure and the interesting biological activity of (-)-callystatin A fueled our interest in the synthesis of this marine natural product. We achieved the total synthesis using a highly convergent approach joining four subunits together with a Wittig olefination, a selective Heck reaction and an aldol reaction as the pivotal steps. The aldol reaction as one of the final transformations during the synthesis opens fast access to a variety of structural analogues and circumvents tedious protecting group manipulations. Here we report an improved synthesis utilizing a modified vinyl iodide which shortens the synthesis by two steps. Additionally, first biological results will be reported.