L-Rhamnal diacetate

Tetronomycin (102), a structurally challenging 3-acyltetronic acid ionophore antibiotic, was isolated from a Streptomyces strain in the early 1980s [71]. The only total synthesis reported so far was accomplished in 1992 by Yoshii and coworkers (Scheme 1.14) [72]. By using as chiral building blocks the ethoxyethyl ether 98 and L-rhamnal diacetate 99, Yoshii reached aldehyde 100, a suitable precursor for the installation of the tetronic moiety. This was achieved by a reaction with the lithium anion of methyl tetronate 101 at —100°C that led to the target after pyridinium chlorochromate (PCC) oxidation and careful deprotection. 

Analogues of daunosamine have been prepared from L-rhamnal diacetate 31 via the known 3-azido-2,3-dideoxy-sugar 32 (Scheme 8). Inversion of configura-... 

Synthesis by Introduction of Two Amino oops. - The 2,4-diamino-2,4,6-trideoxy-L-altroside 111 was synthesized in 10 steps from L-rhamnal diacetate. 

Cycloaddition of trichloroacetyl isocyanate to L-rhamnal diacetate gave the products (9)-(ll), and (9) reacted with a ... 

The L-arabinose derivative 205 provides the starting point for synthesis of the 2-deoxythreose derivative 206, then converted to the acyclic nucleotide analogue 207 (which is twice as active against cytomegalovirus as its (5)-enantiomer). The chiron 208 has been synthesized starting from L-ascorlric acid, while diacetyl-D-rhamnal has been converted to 209 in six steps. The carbohydrate-derived meso epoxide diacetate 210 has been efficiently desymmetrized (to the monoacetate) using... 

Peracetylated D-glucal, D-galactal, and D-rhamnal were selectively deprotected at 04 by treatment with hydrazine acetate in DMF (see Vol.20, Chapter 13, ref.3). The possibility of initial deacetylation at the primary position followed by 4- 6 acetyl migration was excluded on the basis of experiments with deuteroacetylated starting compounds." The 4->6 acetyl migration to give the 3,6-diacetate (14) from its 3,4-isomer (13) has been studied in some detail and optimized in order to prepare (l->4)- and (l- 6)-linked disaccharides from a common carbohydrate aglycon (see Chapter 3). ... 

---