Identification of tuliposide G, a novel glucoside ester-type tuliposide, and its distribution in tulip

Identification of tuliposides K-M in tulip bulbs via an enzyme reaction-based screening method using a tuliposide-converting enzyme

Tuliposides (Pos) are major defense-related secondary metabolites in tulip, having 4-hydroxy-2-methylenebutanoyl and/or (3S)-3,4-dihydroxy-2-methylenebutanoyl groups at the C-1 and/or C-6 positions of d-glucose. The acyl group at the C-6 position is converted to antimicrobial lactones (tulipalins) by an endogenous Pos-converting enzyme. Based on this enzyme activity, we examined tulip bulb extracts and detected HPLC peaks that disappeared following the reaction by the Pos-converting enzyme. Spectroscopic analyses of the three purified compounds revealed that one of them was a glucose ester-type Pos, while the other two were identified as a glucoside ester-type Pos. These compounds were designated as PosK, L, and M. They were specific to bulbs, with the highest content in the outermost layer, but they were markedly less abundant than PosG, the minor bulb Pos we identified earlier. The study results suggest that tulip bulbs contain at least four minor Pos in addition to the major 6-PosA. Although PosK-M were present in almost all of the tested tulip cultivars, they were detected in only a few wild species, indicative of their potential utility as chemotaxonomic markers in tulip. Identification of PosK-M as 6-PosA derivatives unveils the biosynthetic diversity of Pos, the well-known group of secondary metabolites in tulip.

Occurrence of Z-2-oxo-4-methyl-3-pentene-1,5-dioic acid and its regioisomer 4-methylene-2-oxo-glutaric acid in tulip tissues

Although Z-2-oxo-4-methyl-3-pentene-1,5-dioic acid (Z-OMPD) has been identified as a major dicarboxylic acid in tulip tissues, its biosynthetic pathway has not been elucidated. Herein, Z-OMPD was isolated from tulip leaves and chemically synthesized. Comparisons of these samples revealed that Z-OMPD exists as a tautomeric mixture at physiological pH. As a regioisomer of Z-OMPD, we enzymatically and chemically prepared 4-methylene-2-oxo-glutaric acid (4-MEOG) for the first time. Using these compounds as standards, the occurrence of Z-OMPD and 4-MEOG in various tissues of the tulip cultivar "Murasakizuisho" was evaluated directly and by 2,4-dinitrophenylhydrazone derivatization. Z-OMPD was found to be abundant in the aerial tissues, whereas 4-MEOG was almost absent from all tissues. Stability analyses of Z-OMPD and 4-MEOG revealed that no double bond isomerization occurred at physiological pH, suggesting that enzyme systems are responsible for Z-OMPD biosynthesis in tulip tissues.

Tuliposides H-J and Bioactive Components from the Bulb of Amana edulis

Three new tuliposides H-J (1-3) and 11 known compounds were obtained from the methanolic extracts of the bulbs of Amana edulis for the first time. Their structures were elucidated by NMR, MS, and IR spectroscopic data, optical rotation, and Mosher's method. The melanogenesis properties of all the isolates were evaluated in B16 melanoma cells. Consequently, tributyl citrate (9) had anti-melanogenesis activity but was cytotoxic toward B16. (+)-Pyroglutamic acid (4), (+)-butyl 5-oxopyrrolidine-2-carboxylate (6), (-)-3-hydroxy-2-methylbutyrolactone (10), and 5-(hydroxymethyl)furfural (12) had increased melanin productions and tyrosinase activities. Those active components could be further studied as the candidates against melanoma and vitiligo for skin diseases or whitening/hypopigmentation for hair.