Enantioselective Total Synthesis of the Natural γ-Tocopherol Metabolite (S)-γ-CEHC [(S)-LLU-α]

Concise Synthesis of (S)-δ-CEHC, a Metabolite of Vitamin E

Carboxyethyl hydroxychromans (CEHCs) are natural metabolites of vitamin E (VE). Their urinary levels can serve as useful biomarkers for the nutritional assessment of VE. Moreover, specific biological activities of CEHCs deserve further investigation. Here, we report a concise method to build up a chiral 6-hydroxychroman scaffold of VE and CEHCs. The first total synthesis of (S)-δ-CEHC was accomplished in 40% overall yield and 97% ee using a chiral synthon derived from naturally occurring (-)-linalool.

Synthesis of (2R,8' S,3' E)-δ-tocodienol, a tocoflexol family member designed to have a superior pharmacokinetic profile compared to δ-tocotrienol

A group of side chain partially saturated tocotrienol analogues, namely tocoflexols, have been previously designed in an effort to improve the pharmacokinetic properties of tocotrienols. (2R,8'S,3'E,11'E)-δ-Tocodienol (1) was predicted to be a high value tocoflexol for further pharmacological evaluation. We now report here an efficient 8-step synthetic route to compound 1 utilizing naturally-occurring δ-tocotrienol as a starting material (24% total yield). The key step in the synthesis is oxidative olefin cleavage of δ-tocotrienol to afford the chroman core of 1 with retention of chirality at the C-2 stereocenter.

6-Hy-droxy-7,8-dimethyl-chroman-2-one

The title compound, C₁₁H₁₂O₃, is essentially planar, with an r.m.s. deviation of 0.179 Å from the mean plane through the 14 non-H atoms in the mol­ecule. The benzene ring and the pyranone mean plane are inclined at 13.12 (6)° to one another and the pyran­one ring adopts a flattened chair conformation. In the crystal, O—H⋯O hydrogen bonds and C—H⋯O contacts form R₁²(6) rings and link mol­ecules into chains along b. Additional C—H⋯O contacts generate inversion dimers, with R₂²(8) ring motifs, and form sheets parallel to (-102) which are linked by C—H⋯π interactions.

5,6-Dimethyl-1,2,9,10-tetra-hydro-pyrano[3,2-f]chromene-3,8-dione

The title mol­ecule, C₁₄H₁₄O₄, lies on a twofold rotation axis that bis­ects the central benzene ring, with only one half-mol­ecule in the asymmetric unit. The pyran­one systems adopt distorted twist- boat conformations, with the two methyl­ene C atoms displaced by 0.537 (1) and 0.163 (2) Å from the best-fit plane through the remaining five C and O atoms (r.m.s. deviation = 0.073 Å). In the crystal, bifurcated C—H⋯(O,O) hydrogen bonds link pairs of adjacent mol­ecules in an obverse fashion, stacking mol­ecules along c. These contacts are further stabilized by very weak π–π inter­actions between adjacent benzene rings with centroid–centroid distances of 4.1951 (4) Å. Additional C—H⋯O contacts link these stacks, giving a three-dimensional network.

Stereoselective synthesis of the C15-C26 fragment of the antitumor agent (-)-dictyostatin

The synthesis of the C15-C26 fragment of (-)-dictyostatin is reported in 10 steps and 28% overall yield. The key steps are the two stereoselective sulfoxide-directed processes: a Reformatsky-type reaction and a β-keto sulfoxide reduction.