The structures of flazin and YS were determined to be β-carboline derivatives, 1 and 2, substituted with a hydroxymethyl-furan moiety at the 1-position. In 1936, Higashi first found a highly fluorescent compound in sake (Japanese rice wine) lees and named it flazin. Flazin has also been found in Japanese rice vinegar, soy sauce and miso (fermented soy bean paste), but its structure had not been determined. YS (yellow substance) was also isolated from an old sake and soy sauce. Although structural and synthetic studies of YS were reported recently, the spectroscopic data of natural and synthetic YS were inconsistent. Now, we report the structures of flazin and YS isolated from soy sauce. Flazin and YS were isolated from Japanese soy sauce (Ichibiki brand tamari). Crude flazin was precipitated from ether extracts after standing for one week at 20°C, filtered, washed with ether to give a crystalline powder (mp 220-225°C), further purified by recrystallization from methanol to yield flazin (mp 230-232°C) with IR (KBr) νmax 3420, 1601, 1360, 1320 cm⁻¹ and UV (MeOH) λmax 263(26800), 290(22800), 355(11800), 370(12400) nm (ε). The ¹H-NMR spectrum of flazin in DMSO-d₆ showed only broad signals. Flazin was extremely polar with limited solubility in organic solvents and water, requiring derivatization for structural studies. Treatment of flazin with diazomethane in methanol afforded a monomethyl ester (90% yield, mp 199-200°C, MS m/z 322 (M⁺)) whose ¹H-NMR (CDCl₃) indicated a 2,5-disubstituted furan moiety (δ 6.43, d, J=3.5 Hz; 7.38, d, J=3.5 Hz) and a hydroxymethyl group (δ 4.79, br.s). Acetylation of flazin with acetic anhydride/pyridine gave a monoacetate (quantitative yield) with -CH₂OAc (δ 5.23, s). Hydrogenolysis of the monoacetate with H₂/5% Pd-C in methanol gave a methylfuran derivative (95% yield, mp 158-159°C, MS m/z 306 (M⁺)). Further hydrogenation with H₂/20% Pd-C in methanol at 60°C for 2 hr yielded a tetrahydro derivative (85% yield, oil, MS m/z 310 (M⁺)) with a -CHX-CH₂-CH₂-CHX-CH₃ group confirmed by decoupling experiments, transforming the furan moiety to 2,5-disubstituted tetrahydrofuran. The UV and aromatic ¹H-NMR spectra of the methyl ester were similar to methyl β-carboline-3-carboxylate, leading to the conclusion that flazin is 1-(5-hydroxymethyl-2-furyl)-β-carboline-3-carboxylic acid (1). YS was isolated by treating the ether extract with 1N NaOH, acidifying the organic layer with conc. HCl to get YS hydrochloride, which was neutralized with 1N NaOH, extracted with ether, and purified by thin-layer chromatography to yield YS as a yellow powder (mp 186°C, MS m/z 264 (M⁺)). Its ¹H-NMR (CD₃OD) showed signals for a hydroxymethyl group (δ 4.76, s), furan moiety (δ 6.58, d, J=3.5 Hz; 7.21, d, J=3.5 Hz), and aromatic protons. The ¹H-NMR spectrum of YS was similar to flazin methyl ester (except two protons at δ 8.00 and 8.28 ppm) and harmane, with nearly identical UV spectra to harmane, leading to the conclusion that YS is 1-(5-hydroxymethyl-2-furyl)-β-carboline (2). The structure of YS is identical to perlolidin isolated from perennial rye-grass (Lolium perenne L.), Ligusticum chuanxiong (a medicinal plant for angina pectoris) and Korean ginseng, with spectroscopic data consistent with previous reports. The structures of flazin (1) and YS (2) resemble biologically active β-carboline analogs such as pyridindolol (a β-galactosidase inhibitor) and ethyl β-carboline-3-carboxylate (β-CEE, a potent inhibitor of ³H-diazepam binding to brain receptors). Synthetic studies of flazin (1) and biological tests of these β-carboline derivatives are ongoing.