biogenetic engineering by expression of a truncated version of the gene of a
polyketide synthon in a heterologous host Saccharopolyspora erythraea. Only
some selected examples of biologically active natural products with the δ-lactone
framework are represented in Fig. 1.
The biological importance of δ-lactones has sparked enormous interest among
the synthetic chemists and led to the development of a wide variety of powerful
methods for their synthesis. In this chapter, a brief review on selected approaches
for the construction of the saturated δ-lactone framework is presented, focusing
mainly on the ring-closing steps. We have to point out that methods for the
synthesis of unsaturated δ-lactones and their derivatization to saturated δ-lactones
are beyond the scope of this chapter.
2 Lactonization of δ-Hydroxy Acid Derivatives
Lactonization is the most widely used method for the formation of lactones, and
there are numerous examples under this category for the construction of δ-lactones
from the corresponding δ-hydroxy acid derivatives. For example, in 1962, Pappo
Fig. 1 Examples of natural products with δ-lactone framework
Synthesis of Saturated Six-Membered Ring Lactones
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