The structures of illudalic acid (I) and illudinine (11) reported here (Chart I) are both derivable from the same basic "protoilludane" skeleton (111) as those of illudin S and M,lapb illudol'o and marasmic acid.a Illudalic acid was isolated as "a fourth crystalline compound"4 accompanying illudin M in culture liquids of the basidiomycete, Clitocybe illudens. It was acidic and had a molecular weight (cryoscopic) of 365. However, mass spectrometric determination gave the molecular weight 276. This, together with the elemental analysis, led to the correct formula, C16H16O5. The circumstances of isolation of illudinine suggest that it has a special biogenetic relationship to illudalic acid. The alkaloid was obtained from a strain of the fungus originally selected for enhanced production of illudalic acid. In time, this strain apparently mutated, and instead of illudalic acid produced a new compound, illudinine. Illudalic acid (I) had λmax 247, 270 (sh) and 332 mp (ε 29.000, 12,000 and 760) shifting to 260 and 347 mp (ε 16,000 and 2000) in sodium hydroxide solution. The compound dissolved in sodium bicarbonate solution with evolution of carbon dioxide. Potentiometric titration in 80% methyl Cellosolve gave pKa 7.85. The nmr spectrum showed two low-field proton signals, one at τ -2.4 (singlet, which disappeared on adding D2O) and the other at -0.2 (singlet). The first could be assigned to a strongly chelated phenol, and the second to an aldehyde. Acetylation of illudalic acid with acetic anhydride-pyridine at room temperature gave a mixture of products. From this, a crystalline monoacetate (IV) in which the phenolic function was intact was isolated. In the nmr spectrum of IV, a triplet at 3.1 (J = 6 cps), resulting from a shift of the one at 4.2 in the parent compound, indicated the presence in I of a proton α to a secondary hydroxyl. This methine proton was coupled to a methylene group which gave a doublet at τ 6.58. Illudalic acid gave carbonyl bands at 1683 and 1649 cm-1, and characteristic aromatic absorption at 1624 and 1580 cm-1 in its ir spectrum. The 1649-cm-1 band was compatible with an o-hydroxyaldehyde. The position of the band, and the nmr signal (τ -2.4) for the chelated phenol, are in good agreement with values found for o-hydroxy benzaldehydes. The band at 1683 cm-1 was shifted to 1727 cm-1 in the monoacetate which also exhibited bands at 1767 and 1187 cm-1. This, in conjunction with the nmr evidence (signal at τ 4.2 shifting to τ 3.1 on acetylation) and reaction with sodium bicarbonate, was best explained by a δ-lactol structure. The evidence thus far accounted for 10 of the 15 carbon atoms. The other 5 carbon atoms were accounted for by the remaining signals in the nmr spectrum: singlets at τ 6.88 and 7.28, two protons each, and a singlet at τ 8.33, six protons, were compatible only with a cyclopentane possessing a gem-dimethyl group, and fused to the benzene ring. The values are similar to those of 2,2-dimethylindanes, e.g., the indanol derivative V. On treatment with strong alkali, illudalic acid afforded an isomeric lactonic acid. The ir spectrum (vmax 1740, 1680 cm-1) and the nmr spectrum (singlets at τ 7.22, 6.78, 5.55 and 4.47 (two protons each) and a singlet at τ 8.82 (six protons)) indicated structure VI. Formation of VI clearly involves a Canizzaro-type reaction of the aromatic aldehyde and the aldehyde derived from the opening of the lactol ring. Since the aromatic aldehyde has been shown to be ortho to the phenolic hydroxyl, the formation of a δ-lactone allows a complete definition of orientation of substituents in the aromatic ring of I. On heating, acid VI was decarboxylated, and the resulting lactone VII (vmax 1725 cm-1) gave a one-proton singlet at τ 3.2. Hydrogenation of illudalic acid with reduced platinum oxide catalyst in acetic acid gave the acid VIII, C16H20O5, vmax 1682 cm-1. The nmr spectrum showed singlets at τ 5.33, 7.03 and 7.3 (two protons each), two triplets at 7.03 (superimposed on the two-proton singlet) and 6.25, and a singlet at 8.85 (6 H) for the gem-dimethyl. It is interesting to note that another metabolite of Clitocybe illudens, illudoic acid, C15H18O5, resembles this compound closely. Examination of the spectral characteristics of illudoic acid and of its (methylated and acetylated) derivatives led to the tentative structure IX. On hydrogenation over 30% palladized carbon, illudalic acid gave the lactol X in which the aldehyde group is reduced to a methyl. It showed vmax at 1680 cm-1 for the lactol, and the hydrogen-bonded aldehyde absorption at 1649 cm-1 had disappeared. Nmr signals at τ 8.85 (6 H, singlet), 7.84 (3 H, singlet), 7.29 (2 H, singlet), 7.0-6.9 (4 H, a singlet superimposed on a doublet), and 4.25 (1 H, triplet) were in full agreement with this proposed structure. Illudinine, II (mp 228-229' dec; mol wt 271 (mass spectrum); vmax 1690, 1640, 1605 and 1565 cm-1), analyzed for C16H17O3N, and had one O-methyl group. Its ultraviolet absorption spectrum varied with pH as shown in Table I. On treatment with diazomethane it formed a methyl ester (XI) which could be reduced to a primary alcohol (XII), indicating the presence of a carboxyl group. Illudinine showed nmr signals at τ 1.73 (1 H, doublet), 1.47 (1 H, doublet) and 0.6 (1 H, singlet), characteristic of pyridine ring protons of an isoquinoline. Absence of any other low-field signals, and presence of two methylene singlets (6.97, 6.91) and a two-methyl singlet (8.83) suggested the presence of a gem-dimethyl cyclopentane ring fused to the benzene ring of the isoquinoline. Catalytic hydrogenation of XI yielded the tetrahydro derivative XIII in which the low-field signals had disappeared, and there was a singlet (τ 5.59) and a multiplet (τ 6.60) for protons adjacent to nitrogen. On pyridine hydrochloride cleavage of the methoxyl groups illudinine underwent simultaneous decarboxylation to yield an isoquinoline (XIV). Comparison of the ultraviolet absorption spectra of XIV and its methiodide in neutral, acidic and alkaline solution with those of 5-, 6-, 7-, and 8-isoquinolinols under similar conditions established XIV as an 8-hydroxyisoquinoline. It has been possible to obtain this same isoquinoline by treatment of illudalic acid with ammonia and subsequent decarboxylation. This reaction demonstrates the relationship between XIV and I and establishes the structure of illudinine as II. It suggests that illudinine may be derived biogenetically from the protoilludane skeleton III via illudalic acid. This would be in harmony with the observation that illudalic acid could no longer be isolated from the culture that produced illudinine. Like other members of this family of metabolites, illudinine incorporated mevalonic acid-2-C 14.