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The structures of the lichen chromones galapagin, lobodirin, mollin, and roccellin, specific com­ pounds of Roccellaceae (lichens), have been es­ tablished as 1, 2, 3, and 4, respectively, by NOE difference spectroscopoy.

Arthonin, a metabolite of the lichen Arthonia endlicheri has been structurally elucidated as (−)-N-benzoyl-L-valinyl N′-benzoyl-L-isoleucinate. The syntheses of arthonin and iso-arthonin [(−)-N-benzoyl-L-isoleucyl-O-benzoyl-L-valinol] are described. In memory to my dear friend Gunther Snatzke.

The structure of the lichen pigment haemoventosin has been revised to 3,4,6,9-tetrahydro-5,10-dihydroxy-7-methoxy-3S-methyl-1,6,9-trioxo-1H-naphtho-[2,3-c]pyran (3), mainly on the basis of long-range δC/δH correlations observed in 2D HMBC NMR experiments and long-range δH/δD isotope effects observed in partial deuteriation experiments with 10-O-acetylhaemoventosin; ortho- and para-quinonoid structures were distinguished by means of the transacetylation inferred in the sodium dithionite reduction of 10-O-acetylhaemoventosin.

A new myltaylane-type sesquiterpene alcohol and nine known sesquiterpenoids were isolated from Bazzania trilobata. The absolute stereostructure of (1S,4S)-cis-5-hydroxycalamenene was revised to be (1R,4R)-cis-5-hydroxycalamenene by the X-ray crystallographic analysis of its p-bromobenzoate derivative. Four previously known sesquiterpenoids were isolated from Porella canariensis, together with an artefact of a pinguisane-type sesquiterpene lactone. Their structures were determined by the use of extensive NMR techniques.

The regioselectivity of deprotonation/alkylation reactions of η6-1,3-dimethoxybenzene-Cr(CO)3 (5), η6-1,3-dimethoxy-5-methylbenzene-Cr(CO)3 (6) and 2-substituted derivatives of these compounds was investigated. It is shown that the regioselectivity highly depends on the reaction conditions. For instance, deprotonation of η6-1,3-dimethoxy-2-(trimethylsilyl)benzene-Cr(CO)3 (10) with n-BuLi followed by silylation or methylation affords 4-substituted products while the use of LiTMP at −78 °C cleanly gives rise to 5-substituted products. The regioselective alkylation of complexes of type 6 at the 5-methyl group is easily achieved. The usefulness of the latter possibility is demonstrated in a synthesis of olivetol dimethyl ether (33).

Lichen chemistry continues to be a flourishing branch of natural product chemistry. Since the last major review by Elix et al. in volume 35 of this series (274) many new and interesting lichen substances have been isolated and synthesized. This suggests that an update is desirable. As in the previous articles new methods for structure elucidation and synthesis, biosynthesis, chemotaxonomy and biological activities of lichen substances will be discussed. Some other relatively recent treatments of the subject need to be mentioned: A short chapter by Culberson and Elix (100) in Harborne’s Methods in Plant Biochemistry treated lichen constituents. Several minor reviews were published in 1984 (382), 1991 (385) and 1994 (386). Volume III of Galun’s Handbook of Lichenology (311) contains a chapter on chemical constituents of lichens including secondary metabolic products, storage products of lichens, carotenoids and phycobiliproteins.

Pakyonol, a new macrocyclic bisbibenzyl from the liverwort Mannia fragrans , has been assigned structure ( 2 ) mainly on the basis of evidence from COSY and n.O.e. difference experiments.