The
preparation of 2-deoxy-l-ribose derivatives or mirror
image deoxyribonucleosides (l-deoxyribonucleosides) from d-ribose is reported. Starting from inexpensive d-ribose,
an acyclic d-form carbohydrate precursor was synthesized
to study a unique carbonyl translocation process. In this novel radical
reaction, not only was the configuration of the sugar transformed
from the d-form to the l-form, but also deoxygenation
at the C(2) position of the sugar was successfully achieved. This
is one of the most practical methods for converting a d-sugar
to a 2-deoxy-l-sugar in a one-step reaction. To further identify
the reaction product, radical reactions followed by treatment with
1,3-propanedithiol and then benzoylation were performed to afford
a dithioacetal derivative. The stereochemistry and configuration of
the 2-deoxy-l-ribose dithioacetal derivative were confirmed
by its X-ray crystal structure. To further apply this methodology,
a diethyl thioacetal derivative was formed, followed by selective
benzoyl protection, and an NIS-initiated cyclization reaction to give
the desired ethyl S-l-2-deoxyriboside, which
can be used as a 2-deoxy-l-ribosyl synthon in the formal
total synthesis of various l-deoxyribonucleosides, such as l-dT.