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In the previous studies1-4) we have isolated from marine gastropods and a bivalve a number of quater nary ammonium compommds. Some of these com pounds were new as the naturral product and the number of the compounds detected in one species was more than expected from the previous literature. Similar complexlty of the compositlon of these compounds in bivalves was also demonstrated by KONOSU et al.5.6) by the finding of a new betaine, atrinine, and the identi fication of 10 compounds. These results stimulated us to further the search for new quatemary ammonium bases in marine molluscs. In this study the specimens of oyster Classostrea gigas collected at Kesennuma Bay, Miyagi Prefecture, in April 1976 were used. They were first freed of lipids with acetone and the residue was then extracted with boiling methanol. The methanol extracts were suc cessively trcated on cnlumns of the anion-excharige resin (Amberlite IRA-400) and the cation-exchange resin (Dowex 50W-X8). The compounds retained on the latter resin were eluted with hydrochloric acid by increasing stepwise the concentration, as described in the previous report3). The final purification was carried out by preparative paper chromatography on Toyo Filter Paper No. 514 with the fbllowing two sol vents: A) 1-butanol-acetic acid-water (4:1:2) and B) 1-propanol-28% ammonium hydroxide-water (7:1:2). The paper chromatographic examination revealed the presenccof 9 compounds reactive to the Dragendorff reagent. Five of them were isolated and identified as choline, glycine betainc, stachydrile, homarine, and trigonelline by comparing their mass spectra with those obtained in the previous study.3) Supplementary data were also available from the uv spectra in the case of homarine and trigonelline and from the ir spectra in tbe case of glycine betaine, choline, and homarine. Com parison by tlc between the isolated and synthesized specimens with the afore-mentioned two solvents on cellulose layers also confirmed their identity. The sixth compound revealed a strong peak at m/e 79 in its mass spectrum indicating the presence of pyridine nucleus. The uv spectrum was in agreement with the above observation in having an absorption maximum at 258 nm (in water) which did not shift by the change of PH. Subsequent pmr study clearly indicated to a struc ture of N-methylpyridinium. The following signals were observed in the spectrum: a singlet (3H) at δ 4 .1 asslgnable to a methyl group attached to a quatemary nitrogen, a triplet (2H) centered at δ 7 .6 assignable to protons at C-3 and C-5, a triplet (1H) at δ 8.0 assignable to a proton at C-4, and a doublet (2H) centered at δ 8.4 assignable to protons at C-2 and C-6 . The final confirmation of tbe structure was attained by com parison wlth synthetic N-methylpyridinium by mass spectrometry, uv spectrometry, and tlc (Rf 0.59 with solvent A and 0.51 with solvent B). The seventh com pound was also characterized by the presence of pyri dine nucleus as indicated by the peak at m/e 79 in the mass spectrum. The pmr spectrum in D2O showed two singlets at δ 2.9 and 4.1 which were assignable respectively to a methyl group attached to the ring and a methyl group attached to a quaternary nitrogen atom. Insufficient sample size did not allow us to further analyze the signals due to other protons on the ring. However, the position of the C-methyl group was pre sumed to be either at C-2 or C-3 from the uv absorp tion maximum at 262 nm in aqueous solution (ref.7) α-picoline 262 nm, β-picoline 263 nm, γ-picoline 255 nm). The uv spectrum of synthetic N-methyl-αpicolinium coincided well with that of the isolated speci men while that of N-methyl-β-picolinium was slightly different in having the maximum at 265 nm. Further evidence was obtained by tlc comparison where the iso lated specimen was distinguishable from N-methyl-β picolinium but was indistinguishable from N-methyl-αpicolinium (Rf 0.56 with both solvents A and B). Attempts to isolate two other compounds were unsuc cessful owing to their insufficient sample size and their structures remain unidentified. Although the present study was not carried out quantitatively it was noticed that glycine betaine was the most abundant. Choline and homarine also were present in considerable amount but the amount of other compounds were quite small. N-Methylpyridinium has been known to be present in the crab, sea anemone, and mussel8). However, no previous report seems available about the occurrence on N-methyl-α-picolinium in the natural source.

Identification of <i>N</i>-Methyl-&alpha;-picolinium and Other Quaternary Ammonium Compounds from the Oyster

Identification of <i>N</i>-Methyl-α-picolinium and Other Quaternary Ammonium Compounds from the Oyster