Efficient synthesis of cryptophycin-52 and novel para- Alkoxymethyl unit A analogues
Cryptophycins are a family of highly cytotoxic, cyclic depsipeptides. They display antitumour activity that is largely maintained for multidrug-resistant tumour cells. Cryptophycins are composed of four building blocks (units A-D) that correspond to the respective amino and hydroxy acids. A new synthetic route to unit A allows the selective generation of all four stereogenic centres in a short, efficient and reliable synthesis and con-tributes to an easier and faster synthesis of cryptophycins. The first two stereogenic centres are introduced by a catalytic asymmetric dihydroxylation, whereas the remaining two stereogenic centres are introduced with substrate control of diastereoselectivity. The stereogenic diol function also serves as the epoxide precursor. The approach was used to synthesise the native unit A building block as well as three paraalkoxymethyl analogues from which cryptophycin-52 and three analogous cryptophycins were prepared. Macrocyclisation of the seco-depsipeptides was based on ring-closing metathesis.
A convenient synthesis of methyl- and isopropyl-benzyl ethers using silver(II) oxide as reagent
Substituted bromomethyl- and chloromethylbenzenes and bis(bromomethyl) benzenes were directly converted, in high yields, to the corresponding methyl- and isopropyl-benzyl ethers by treatment with silver(II) oxide in methanol or isopropanol.
Ortiz,Walls,Yuste,Barrios,Sanchez-Obregon,Pinelo
p. 749 - 756
(2007/10/02)
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