Methyl protolichesterinate

Scheme 28. Synthesis of ( )-methyl protolichesterinate and ( )-methyl allo-protoliche-sterinate (512)...

Lichesterylic acid and methyl protolichesterinate have been found in Cetraria islandica (555) the latter ester was prepared from the potassium salt of protolichesterinic acid and methyl iodide 413). Allo-protolichesterinic acid adds diazomethane to form isomeric pyrazoline methylesters, the stereochemistry of which was established by their respective CD spectra. Hydrogenation of allo-protolichesterinic acid with Pd-C in acetic acid produces a mixture of (-)-dihydro-allo-protolichesterinic acid (33), (-)-nephromopsinic acid (34) and (-)-lichesterinic acid (35) (see Scheme 34). 

Usnic acid Methyl a-orcinolcarboxylate Ethyl hematommate Diffractaic acid (+) Protolichesterinic acid Human keratinocyte cell line HaCaT Kumar and Muller (1999)... 

Scheme 29. Synthesis of racemic protolichesterinic acid by carboxylation of y-butyrolactones with methyl methoxymagnesium carbonate...

The ORD spectra shown in Fig. 3 allow an easy differentiation between (-)-methyl dihydro-allo-protolichesterinate (36), (-)-methyl nephromopsinate (37), (-)-methylroccellarate (38) and (-)-methyl dihydroprotolichesterinate (39) (see Fig. 3). 

Martin J, Watts PC, Johnson F (1974) Carboxylations of y-Butyrolactones with Methyl Methoxymagnesium Carbonate. A New Synthesis of dl-Protolichesterinic Acid. J Org Chem 39 1676. 

---