Divergent total synthesis of d-ribo-phytosphingosine and l-ribo-phytosphingosine from d-ribose

Divergent access to a novel 3,4-diaminophytosphingosine-like ceramide via sequential Overman rearrangement

A straightforward approach to a novel phytosphingosine-like ceramide has been accomplished. The cornerstone features of this divergent synthesis are a cascade Overman rearrangement of tris(imidate) to introduce three desired stereogenic centres via sequential chirality transfer and an effective olefin cross-metathesis to install a long side chain. The final unusual phytoceramides were evaluated for their capacity to inhibit the proliferation of cancer cell lines. The preliminary results revealed that compound 21 exhibits promising anticancer activity against HeLa and HCT-116 cells as well as the excellent selectivity in cytotoxicity (malignant vs non-malignant cell lines).

Straightforward access to novel cytotoxic phytosphingosine-like aminotriols from l-erythrose chiron

A divergent approach to a small library of long-chain 6-amino-1,4,5-triols as novel phytosphingosine-type entities, together with their preliminary cytotoxic evaluation, was achieved. Construction of the target compounds addressed two key aspects. First, the installation of a carbon-nitrogen bond via two prototypes of [3,3]-sigmatropic rearrangements and second the introduction of an alkyl side chain unit by using a late stage olefin cross-metathesis process. As shown in cell viability experiments, the corresponding HCl salts proved to be the most cytotoxic derivatives among all the tested substances, with IC₅₀ values in the lower micromolar range on the Jurkat, HeLa and HCT-116 cell lines.

Total Synthesis of Phospholipomannan of Candida albicans

First, total synthesis of the cell surface phospholipomannan anchor [β-Manp-(1 → 2)-β-Manp]_n-(1 → 2)-β-Manp-(1 → 2)-α-Manp-1 → P-(O → 6)-α-Manp-(1 → 2)-Inositol-1-P-(O → 1)-phytoceramide of Candida albicans is reported. The target phospholipomannan (PLM) anchor poses synthetic challenges such as the unusual kinetically controlled (1 → 2)-β-oligomannan domain, anomeric phosphodiester, and unique phytoceramide lipid tail linked to the glycan through a phosphate group. The synthesis of PLM anchor was accomplished using a convergent block synthetic approach using three main appropriately protected building blocks: (1 → 2)-β-tetramannan repeats, pseudodisaccharide, and phytoceramide-1-H-phosphonate. The most challenging (1 → 2)-β-tetramannan domain was synthesized in one pot using the preactivation method. The phytoceramide-1-H-phosphonate was synthesized through an enantioselective A³ three-component coupling reaction. Finally, the phytoceramide-1-H-phosphonate moiety was coupled with pseudodisaccharide followed by deacetylation to produce the acceptor, which on subsequent coupling with tetramannosyl-H-phosphonate provided the fully protected PLM anchor. Final deprotection was successfully achieved by Pearlman's hydrogenation.

Stereoselective Synthesis of β-Amino Ynones by the Addition of Alkynones to Nonracemic Sulfinimines: Formal Total Synthesis of l-Xylo and l-Arabino Phytosphingosines

The addition of silyl enol ethers obtained from ynones to sulfinimines furnished the corresponding β-sulfinamido ynones in a very good yield and diastereoselectivity. The formed ynones serve as precursors amenable for the synthesis of bioactive compounds. This has been illustrated in the synthesis of l-xylo and l-arabino phytosphingosines.