Antonio Abad

Synthesis of (+)-podocarp-8(14)-en-13-one and methyl-(+)-13-oxo-podocarp-8(14)-en-18-oate from abietic acid

Abstract An efficient method for the preparation of (+)-podocarp-8(14)-en-13-one 6 and methyl-(+)-13-oxo-podocarp-8(14)-en-18-oate 8 from abietic acid is described.

Stereoselective synthesis of polyoxygenated atisane-type diterpenoids

Abstract A new stereoselective approach to polyoxygenated atisane-type diterpenes starting from (S)-(+)-carvone is described. The key steps involve an intramolecular Diels–Alder reaction, an unusual intramolecular diazo ketone cyclopropanation of an unsaturated ketone, and a regioselective endocyclic cleavage of a cyclopropyl carbinyl radical as key synthetic steps. The synthesis of the bioactive polyoxygenated atisanes atis-16(17)-en-3,14-dione ( 2 ) and 3R-hydroxy-atis-16(17)-en-2,14-dione ( 3 ) following this approach is presented.

Spongian pentacyclic diterpenes. Stereoselective synthesis of aplyroseol-1, aplyroseol-2 and deacetylaplyroseol-2

Natural spongian pentacyclic diterpenes aplyroseol-1 19, aplyroseol-2 18 and deacetylaplyroseol-2 17 have been synthesized in enantiomerically pure form from (+)-podacarp-8(14)-en-13-one 3. Key intermediate in these syntheses is a suitably substituted acid-dialdehyde 2, which is prepared from enone 3 by a sequence of transformations involving stereoselective introduction of a C-7 oxygen functionality, photoaddition of acetylene to the C(8)–C(14) double bond to form a cyclobutene ring system, reductive cyanation of the C-13 carbonyl group, hydrolysis of the resulting nitrile group, and ozonolysis of the cyclobutene moiety. An intramolecular participation of the 7α-hydroxy group in the hydrolysis of the 13α-nitrile 8 is set in focus.

Vascular activity of a natural diterpene isolated from Croton zambesicus and of a structurally similar synthetic trachylobane.

The aim of this study was to determine the vasorelaxant activity of a natural diterpene extracted from Croton zambesicus, ent-18-hydroxy-trachyloban-3-one (DT6), and a synthetic diterpene of similar structure, ent-trachyloban-14,15-dione (DT10) in rat aorta. DT6 and DT10 inhibited aorta contraction in a concentration-dependent manner. Both were more potent inhibitors of KCl-evoked contraction than noradrenaline-evoked contraction. Nitric oxide (NO) synthase inhibition did not significantly affect DT6 effect whereas it significantly decreased DT10 inhibitory potency. In fura-2 loaded aorta rings, DT10 simultaneously inhibited KCl-evoked contraction and cytosolic calcium increase in a concentration-dependent manner. Furthermore, DT10 significantly inhibited calcium channel current recorded by the patch-clamp technique in human neuroblastoma cells SH-SY5Y. However, despite potentiation of 8-bromo-cGMP-response, DT6 and DT10 as verapamil depressed acetylcholine-evoked relaxation, DT6 being the most potent, while only DT6 and DT10 depressed SNAP-evoked relaxation. In conclusion, these data suggest that vasorelaxant activity of diterpenes (DT) is associated with the blockade of L-type voltage-operated calcium channels. Inhibition of NO-dependent relaxation by DT could be related to a decrease in NO availability.

Enantioselective synthesis of herbertane sesquiterpenes: synthesis of (−)-α-formylherbertenol

Abstract The synthesis of 4-hydroxy-3-[(1 S )-1,2,2-trimethylcyclopentyl]benzaldehyde [(−)-α-formylherbertenol 1 ], a herbertane-type sesquiterpene isolated from the leafy liverwort Herberta adunca , from β-cyclogeraniol is described. The synthesis is based on the previously described preparation of an enantiopure 1,2,2-trimethylcyclopentane synthon from which the characteristic aromatic moiety of 1 is elaborated, using a Robinson annulation and a palladium-catalysed methoxycarbonylation of an aryl triflate as key synthetic steps. The synthesis of the natural sesquiterpene (−)-α-herbertenol, also a natural sequiterpene, using the same methodology is also described.

Podocarpane-to-spongian skeleton conversion. Synthesis of (+)-isoagatholactone and (–)-spongia-13(16),14-diene

A stereoselective synthesis of the spongian diterpenes (+)-isoagatholactone 5 and (–)-spongia-13(16),14-diene 6 is achieved starting from (+)-podocarp-8(14)-en-13-one 3 (R = H)via the common intermediate β-hydroxy ketone 13.

New route to herbertanes via a Suzuki cross-coupling reaction: synthesis of herbertenediol

Abstract The synthesis of herbertenediol, a relevant member of the herbertane-type sesquiterpene family, is described. The synthesis is based on a new general approach to this group of sesquiterpenes where the herbertane skeleton is constructed using a Suzuki cross-coupling reaction and a [2,3]-sigmatropic Still–Wittig rearrangement as key synthetic steps.

Synthesis of (−)-auricularic acid and its C-4 epimer the absolute configuration of auricularic acid

Abstract A synthesis of (−)-auricularic acid (2a) starting from methyl (+)-13-oxo- podocarp-8(14)-en-19-oate (3a) and a synthesis of its C-4 epimer (2b) starting from methyl (+)-13-oxopodocarp-8(14)-en-18-oate (3b) are described. The absolute configuration of natural auricularic acid is stablished as (4R, 5S, 8S, 9R, 10S, 14S).

Synthesis of oxygenated spongiane-type diterpenoids from carvone

Abstract A new diastereoselective approach to oxygenated spongiane diterpenes starting from ( R )-(−)-carvone is described. The carvone is incorporated as the B ring in the final spongiane framework using a B→AB→ABC→ABCD approach, which involves an intramolecular Diels–Alder reaction and the regioselective ring-opening of a dihydrofuran ring as key synthetic steps. The structure of the key intermediate in this approach has been verified by X-ray crystallography.

Synthesis of Highly Functionalised Enantiopure Bicyclo(3.2.1)- octane Systems from Carvone

The commercially available monoterpene carvone has been efficiently converted into the tricyclo[3.2.1.0(2.7)]octane and bicyclo[3.2.1]octane systems characteristic of some biologically active compounds. The sequence used for this transformation involves as key features an intramolecular Diels-Alder reaction of a 5-vinyl-1,3-cyclohexadiene and a cyclopropane ring opening.