Tuliposide A

6-Tuliposides A (6-PosA) and B (6-PosB) are major secondary metabolites in tulip (Tulipa gesneriana), having an acyl group at the C-6 position of D-glucose. They serve as precursors of the antimicrobial α-methylene-γ-butyrolactones tulipalins A (PaA) and B (PaB). The conversions of 6-PosA/6-PosB to PaA/PaB are catalyzed by tuliposide-converting enzymes A and B (TCEA and TCEB), respectively. A minor Pos, 1-PosA, which has the acyl group at the C-1 position of D-glucose, has been identified in some wild tulip species, but availability of this compound is limited. Here, by using the TCEs, we established a facile enzymatic process for 1-PosA synthesis from the naturally occurring 1,6-diacyl-glucose type of Pos (PosD and PosF). We first discovered that TCEA and TCEB react preferentially with PosD and PosF, respectively, to form 1-PosA and the corresponding Pa derived from the 6-acyl group, demonstrating that the TCEs specifically acted on the 6-acyl group, but not the 1-acyl group, of the substrates. Using TCEB, 300 mg of PosF was completely converted to 1-PosA and PaB in 10 min at room temperature. Then, 160 mg of 1-PosA (75% molar yield) was purified by column chromatography. This one-step enzymatic process dramatically improves accessibility to 1-PosA.

6-Tuliposides A (PosA) and B (PosB) are glucose esters accumulated in tulip (Tulipa gesneriana) as major defensive secondary metabolites. Pos-converting enzymes (TgTCEs), which we discovered previously from tulip, catalyze the conversion reactions of PosA and PosB to antimicrobial tulipalins A (PaA) and B (PaB), respectively. The TgTCEs, belonging to the carboxylesterase family, specifically catalyze intramolecular transesterification, but not hydrolysis. In this report, we synthesized analogues of Pos with various alcohol moieties, and measured the TgTCE activity together with a determination of the kinetic parameters for these analogues with a view to probe the substrate recognition mechanism of the unique non-ester-hydrolyzing TgTCEs. It was found that d-glucose-like structure and number of the hydroxyl group in alcohol moiety are important for substrate recognition by TgTCEs. Among the analogues examined, 1,2-dideoxy analogues of PosA and PosB were found to be recognized by the TgTCEs more specifically than the authentic substrates by lowering Km values. The present results will provide a basis for designing simple, stable synthetic substrate analogues for crystallographic analysis of TgTCEs.

Tulipalin A induced phytotoxicity is a persistent allergic contact dermatitides documented in floral workers exposed to Alstroemeria and its cultivars.[1] The causative allergen is tulipalin A, a toxic glycoside named for the tulip bulbs from which it was first isolated.[2] The condition is characterized by fissured acropulpitis, often accompanied by hyperpigmentation, onychorrhexis, and paronychia. More of the volar surface may be affected in sensitized florists. Dermatitis and paronychia are extremely common conditions and diagnostic errors may occur. A thorough patient history, in conjunction with confirmatory patch testing with a bulb sliver and tuliposide A exposure, can prevent misdiagnosis. We report a case of Tulipalin A induced phytotoxicity misdiagnosed as an unresolved tinea manuum infection in a patient evaluated for occupational exposure.