Chemical Revision of Hypogymnia hengduanensis

Abstract

A new lichen species with isidia Hypogymnia hengduanensis, containing barbatic acid and atranorin, was described by Wei in 1984. This chemical revision, using the combined methods of microcrystal test (MCT), thin-layer chromatography (TLC), and high-performance liquid chromatography (HPLC) shows that diffractaic acid is the major compound in addition to barbatic acid and atranorin in H. hengduanensis. Lichen substances, in combination with morphology and distribution, are of great importance in the classification of lichens, especially of lichen genus Hypogymnia (Nyl.) Nyl. A new species with isidia, H. hengduanensis Wei, containing barbatic acid and atranorin was described by Wei (Wei 1984, 1986). During the study of the lichen flora of China, extensive collections of the genus Hypogymnia with isidia were examined. Among them, a chemical revision of H. hengduanensis shows that diffractaic acid is the major compound, in addition to barbatic acid and atranorin. As a consequence, the type collections of H. hengduanensis were reexamined by standardized thin-layer chromatography (TLC) and microcrystal test (MCT), in combination with high-performance liquid chromatography (HPLC). MATERIALS AND METHODS Type collection of H. hengduanensis Wei ssp. hengduanensis were examined: Sichuan Province, Kangding district, Yulinkong, Gomba La, on the tree bark of Betula sp., elev. 3,700 m, October 19, 1934, collected by H. Smith 14078 (isotype, HMAS-L). Yunnan Province, Lijiang district, Heibaishui tree farm, on Rhododendron sp., elev. 3,140 m, November 10, 1980, collected by Y. M. Jiang 131 (paratype, HMAS-L). Also, the type collection of H. hengduanensis ssp. kangdingensis Wei was examined: Sichuan Province, Kangding district, Gomba La, on the tree bark of Rhododendron sp., elev. 3,700 m, July 22, 1934, H. Smith 14061 (isotype, HMAS-L). These specimens were analyzed by TLC using the three-solvent-system method standardized for lichen products (Culberson 1974; White & James 1985) except that methyl tert.-butyl ether was used in place of diethyl ether for solvent B (Culberson & Johnson 1982) and MCT (Asahina 1936, 1937). The isotype specimen of H. hengduanensis ssp. hengduanensis was analyzed by high-performance liquid chromatography in addition to MCT and TLC. High-performance Liquid Chromatography.-Thallus fragments were extracted first with benzene at room temperature and then four times with warm (380C) acetone. A portion of the residue was redissolved in 3-5 drops of methanol. Small volumes (2-4 pil) were chromatographed on a precolumn (50 x 4.6 mm I.D.) and an analytical column (250 x 4.6 mm I.D.) filled with YWGCH (C18, 10 im) [Tianjin Second Factory of Chemical Reagents, China] with CH3OH: THF: 0.5% H3PO4 mobile phase of 22.5:22.5:55, v:v:v, at 1 ml/min, at 1,700 psi. Representative retention times for the following different compounds were: diffractaic acid, 2.80 min atranorin, 3.73 min. and barbatic acid, 4.06 min. Identification of atranorin, diffractaic acid, and barbatic acid was made by comparison with authentic samples for both the TLC and HPLC analyses given kindly by S. Huneck. RESULTS AND DISCUSSION The MCT gave abundant crystals of diffractaic acid in GE. By TLC, solvent B showed a strong spot of diffractaic acid (R, class 6; R, X 100 = 58) and a trace of barbatic acid (R, class 6; R, X 100 = 69), which separated just above. Diffractaic and barbatic acids ran together in solvents A (R, class 4) and C (R, class 6). A trace of atranorin was detected in all three solvents. It is clear that the mixture of barbatic and diffractaic acids was mistaken by the senior author for barbatic acid in the type description of H. hengduanensis, using solvent C only and without authentic samples for comparison. The HPLC analysis (Fig. 1) agreed with the TLC result: Peak D is the major compound diffractaic acid, and the trace peaks A and B are atranorin and barbatic acid, respectively. By MCT, abundant crystals of the major substance, diffractaic acid, were confirmed in GE, but the low concentrations of atranorin and barbatic acid were not detected. Thus, H. hengduanensis contains diffractaic acid as the major compound accompanied by trace amounts of barbatic acid and atranorin. Diffractaic acid has been reported from some species of Hypogymnia as an accessory compound, often in low concentration, accompanying larger amounts of the p-orcinol depsidone physodalic 0007-2745/98/556-557$0.35/0 This content downloaded from 157.55.39.78 on Mon, 20 Jun 2016 07:30:18 UTC All use subject to http://about.jstor.org/terms 1998] WEI & BI: CHEMICAL REVISION OF HYPOGYMNIA 557