The depsidones divaronic acid (24) (8-hydroxy-3-methoxy-1,6-dipropyl-11- oxo -11H- dibenzo [ b,e ][1,4]dioxepin-7-carboxylic acid) and stenosporonic acid (25) (8-hydroxy-3-methoxy-6-pentyl-l-propyl-ll-oxo-l1H-dibenzo[ b,e ][1,4]dioxepin-7-carboxylic acid) have been prepared by unambiguous synthesis, and have been shown to cooccur with colensoic acid, atranorin and chloroatranorin in the lichen Paraparmelia mongaensis. The syntheses employed a novel biomimetic-type approach which involved a Smiles rearrangement of a precursor meta-depside in the key step. This rearrangement has important biosynthetic implications and may account for the natural occurrence of isostructural depside-depsidone pairs.
The depsidones norpannarin (4) and norargopsin (5) have been prepared by unambiguous synthesis and shown to co-occur with nordechloropannarin (7), pannarin (3) and argopsin (2) in Erioderma chilense.
The lichen diphenyl ether epiphorellic acid 1 [6-hydroxy-3-(5′-hydroxy-2′-methoxycarbonyl- 3′-pentylphenoxy)-4-methoxy-2-pentylbenzoic acid] (5) has been prepared by unambiguous synthesis. The synthesis employed a biomimetic -type approach which envolved a Smiles rearrangement of a precursor meta- depside in the key step.
The preparation of a series of porphyrins substituted with butyric acid side chains is described and efforts to achieve the intramolecular cyclization of this substituent are discussed. Attempts to prepare a stable spiro ketone by cyclization onto a β- pyrrolic carbon have not met with success but the synthesis of a seven- membered ring ketone by cyclization onto a meso -carbon has been completed. Reduction of this ketone has led to the synthesis of the petroporphyrin (1d). Some comments are offered concerning the origin of the isomeric petroporphyrin (19a) which bears a methylated six- membered ring sytem fused to the porphyrin macrocycle.
The preparation of a series of porphyrins such as (III), substituted with butyric acid side chains, is described and efforts to achieve the intramolecular cyclization of this substituent are discussed.
345ChemInform Abstract The title compounds (Va) (divaronic acid) and (Vb) (stenosporonic acid) are shown to cooccur with colensoic acid, atranorin, and chloroatranorin in the lichen Paraparmelia mongaensis. A novel biomimetic-type approach to (Va) and (Vb) starts with the readily accessible educts (I) and (II) and involves a Smiles rearrangement of the depside esters (III) to the ethers (IVa), (IVb) as the key step. This rearrangement has important biosynthetic implications and may account for the natural occurrence of isostructural depside-depsidone pairs. Smiles rearrangements of unactivated meta-depsides are reported as model reactions.
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