Highly efficient synthesis of chiral aminoalcohols and aminodiols with camphane skeleton

Synthesis and Investigation of Pinane-Based Chiral Tridentate Ligands in the Asymmetric Addition of Diethylzinc to Aldehydes

A library of pinane-based chiral aminodiols, derived from natural (−)-β-pinene, were prepared and applied as chiral catalysts in the addition of diethylzinc to aldehydes. (−)-β-Pinene was reacted to provide 3-methylenenopinone, followed by a reduction of the carbonyl function to give a key allylic alcohol intermediate. Stereoselective epoxidation of the latter and subsequent ring opening of the resulting oxirane with primary and secondary amines afforded aminodiols. The regioselectivity of the ring closure of the N-substituted secondary aminodiols with formaldehyde was examined and exclusive formation of oxazolidines was observed. Treatment of the allylic alcohol with benzyl bromide provided the corresponding O-benzyl derivative, which was transformed into O-benzyl aminodiols by aminolysis. Ring closure of the N-isopropyl aminodiol derivative with formaldehyde resulted in spirooxazolidine. The obtained potential catalysts were applied in the reaction of both aromatic and aliphatic aldehydes to diethylzinc providing moderate to good enantioselectivities (up to 87% ee). Through the use of molecular modeling at an ab initio level, this phenomenon was interpreted in terms of competing reaction pathways. Molecular modeling at the RHF/LANL2DZ level of theory was successfully applied for interpretation of the stereochemical outcome of the reactions leading to display excellent (R) enantioselectivity in the examined transformation.

Stereoselective synthesis and application of isopulegol-based bi- and trifunctional chiral compounds

A new family of isopulegol-based bi- and trifunctional chiral ligands such as triols, tetrols, aminodiols and aminotriols was developed from commercially available (−)-isopulegol with antibacterial, antifungal and antioxidant activities.

Stereoselective Syntheses and Application of Chiral Bi- and Tridentate Ligands Derived from (+)-Sabinol

A library of bidentate diols, as well as tridentate triols and aminodiols, derived from (+)-sabinol, was synthesized in a stereoselective manner. Sabinol was transformed into allylic trichloroacetamide via Overman rearrangement of the corresponding trichloroacetimidate. After changing the protecting group to Boc, the enamine was subjected to stereospecific dihydroxylation with OsO₄/NMO, resulting in the (1R,2R,3R,5R)-aminodiol diastereomer. The obtained primary aminodiol was transformed to a secondary analogue. The ring closure of the N-benzyl-substituted aminodiol with formaldehyde was investigated and regioselective formation of the spiro-oxazolidine ring was observed. Hydroboration or dihydroxylation of sabinol or its benzyl ether with OsO₄/NMO resulted in the formation of sabinane-based diols and triols following a highly stereospecific reaction. Treatment of sabinol with m-CPBA afforded O-benzoyl triol as a diastereoisomer of the directly dihydroxylated product, instead of the expected epoxy alcohol. The resulting aminodiols, diol, and triols were applied as chiral catalysts in the reaction of diethylzinc and benzaldehyde from moderate to good selectivity.

Antiviral activities of compounds from aerial parts of Salvia plebeia R. Br

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia plebeia R. Br. is an edible plant widely spread in many countries. It has been used as a traditional medicine to treat common cold, flu, cough, hepatitis, hemorrhoids, etc. The purpose of the study is to explicate antiviral compounds responsible for its traditional use for the common cold or flu.

MATERIALS AND METHODS

The methanolic extract of the aerial parts of S. plebeia was extracted with CHCl₃, EtOAc, and n-BuOH, successively. The EtOAc and CHCl₃ fractions were subjected to a successive of chromatographic method, which led to the isolation of fourteen compounds. Inhibition activities of the isolated compounds were evaluated against influenza A (H1N1) neuraminidase.

RESULTS

Chemical investigation of the methanolic extracts of S. plebeia resulted in the isolation of two novel benzoylated monoterpene glycosides, named as plebeiosides A (1) and B (2), together with twelve known compounds including four flavonoids (4-5, 7, 10), two sesquiterpenoids (8, 12), four phenolics (9-10, 13-14), a steroid (6), and a triterpenoid (3). Their chemical structures were elucidated based on spectroscopic data and absolute stereochemistries of 1 and 2 were determined by comparison of optical rotations of their hydrolysates with literature values. Compounds 5, 7, 9, and 11 exhibited potent enzymatic inhibition against H1N1 neuraminidase (IC₅₀ values ranging from 11.18±1.73 to 19.83±2.28μM). Furthermore, two flavonoids (5 and 7) and one rosmarinic acid methyl ester (9) reduced cytopathic effects of the H1N1 virus during replication.

CONCLUSIONS

The antiviral activities of the flavonoids and phenolics isolated from the extracts of S. plebeia supported the traditional application of this medicine on common cold or flu. In this study, benzoylated monoterpene glycosides were first found to exist in this species. Moreover, the present study suggested potential of three compounds (5, 7, and 9) to be new lead structures for the development of new neuraminidase inhibitors in the future.