Juan D. Hernández

Generation of the new quirogane skeleton by a vinylogous retro-Michael type rearrangement of longipinene derivatives

Abstract A new tricyclic hydrocarbon skeleton, named quirogane, was prepared by a vinylogous retro-Michael type molecular rearrangement of (4R,5S,7R,8R,9S,10R,11R)-7,8-diacetyloxy-9-mesyloxy-1-oxolongipin-2-ene (5). A remarkable difference in chemical behavior as compared to the corresponding 2,3-dihydroderivative of 5 is explained in terms of the stability of anionic intermediates, which were evaluated by AM1 calculations. The structure of the quirogane skeleton was confirmed by single crystal X-ray diffraction analysis of quirogadiene 6. A [2+2] photochemical cyclization of 6 afforded the highly strained pentacyclic sesquiterpenoid (10).

Oplopanes from the leaves of Senecio mexicanus

Abstract The leaves of Senecio mexicanus afforded three known oplopane derivatives previously found in the roots of the plant and a new oplopane whose structure and stereochemistry followed from X-ray crystallography.

Minor oplopanes from Senecio mexicanus

Abstract Oplopenone and four new oplopane derivatives were isolated from the roots of Senecio mexicanus. Their structures follow from spectral data and the stereochemistry of three of these compounds was determined by single crystal X-ray diffraction studies.

Longipinene derivatives from Stevia origanoides

Abstract The roots of Stevia origanoides afforded three new longipinene derivatives, their structures being established by spectroscopic methods and chemical transformations. The structure and stereochemistry of one of these compounds is further supported by single crystal X-ray analysis of a derivative.

Isolation and preparation of two longipinene derivatives from Stevia subpubescens

Abstract The roots of Stevia subpubescens Lag. afforded longicyclene, longipin-2-ene-7β,9α-diol-1-one diangelate and longipin-2-ene-7β,9α-diol-1-one 7-angelate-9-seneciate. A synthetic pathway involving the protection of the C-7 hydroxyl group of longipin-2-ene-7β,9α-diol-1-one with p-nitrobenzoyl chloride allowed the preparation of the 7-angelate-9-seneciate, while the diangelate was prepared by direct esterification.

Areolal, a thymol from Piptotrix areolare

Abstract From the roots of Piptotrix areolare, a new natural thymol aldehyde, areolal, was obtained, and the structure elucidated by spectral analysis and chemical methods.

A regioselective Wagner–Meerwein rearrangement directed towards the six-membered ring of the longipinane skeleton

Abstract A Wagner–Meerwein rearrangement was selectively promoted towards the six-membered ring of (1R,3S,4S,5S,7R,9R,10R,11R)-7,9-diacetyloxy-1-hydroxylongipinane ( 7 ) to generate a series of compounds which contain a new carbocyclic skeleton named uruapane. Their structures were elucidated by 1D and 2D NMR data in combination with the X-ray diffraction analysis of 9 . Molecular modeling was used to study the reaction mechanism and deuterium labeling was employed to confirm two consecutive hydride shifts which occurred during formation of 8 .

Longipinene derivatives from Stevia porphyrea

The new longipinene derivatives 8α-angeloyloxy-7β-hydroxy-9α-isovaleroyloxylongipin-2-en-1-one, 7β-angeloyloxy-8α,9α-dihydroxylongipin-2-en-1-one and 7β-angeloyloxy-9α-hydroxy-8α-isovaleroyloxylongipin-2-en-1-one together with five known longipinenes, friedelin and stigmasterol were isolated from the roots of Stevia porphyrea. The positional assignment of individual ester residues was done by HMBC experiments.

An oplopane from Senecio mexicanus

Abstract The roots of Senecio mexicanus afforded a new oplopane derivative whose structure was elucidated by spectroscopic methods and by treatment with p -toluenesulphonic acid, which yielded three isomeric substances. The stereochemistry of the natural product followed from X-ray crystallography and its absolute configuration from the optical activity.

Longipinene derivatives from Stevia serrata

Five new longipinene derivatives, together with three known substances, were isolated from the roots of Stevia serrata. The new structures were established by spectroscopic and chemical methods.