Surprising Structural Lability of a Cysteine-S-Conjugate Precursor of 4-Methyl-4-sulfanylpentan-2-one, a Varietal Aroma in Wine of Vitis vinifera L. cv. Sauvignon Blanc
✍ Scribed by Svitlana Shinkaruk; Cécile Thibon; Jean-Marie Schmitter; Pierre Babin; Takatoshi Tominaga; Marie Degueil; Bernard Desbat; Christophe Jussier; Bernard Bennetau; Denis Dubourdieu; Catherine Bennetau-Pelissero
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 313 KB
- Volume
- 5
- Category
- Article
- ISSN
- 1612-1872
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✦ Synopsis
Abstract
4‐Methyl‐4‐sulfanylpentan‐2‐one (1; 4MSP) provides a characteristic aroma compound of wines made from Vitis vinifera L. cv. Sauvignon blanc. 4MSP has a strong box‐tree odor with a very low perception threshold and is derived from the cysteinylated precursor S‐(1,1‐dimethyl‐3‐oxobutyl)cysteine (4; P‐4MSP). P‐4MSP is transformed into 4MSP during alcoholic fermentation and is an excellent marker of varietal aroma potential. An improved synthesis of P‐4MSP as well as of its deuterium‐labeled analogue [D~6~]‐P‐4MSP is described. Several analytical methods (NMR, IR, LSI‐MS, GC/MS, ESI‐MS^n^) were combined to elucidate spontaneous reversible structural changes of P‐4MSP at different pH values. At low pH, P‐4MSP has a linear keto form. The keto–enol tautomerism was observed at neutral pH. At pH 8, the formation of N‐substituted intramolecular hemiaminal was characterized by ESI‐MS and ESI‐MS^n^ experiments. The hemiaminal loses H~2~O at high pH to produce a cycloimine, which is easily opened by acid hydrolysis. The keto–enol tautomerism explained the incorporation of only six D‐atoms during the preparation of the P‐4MSP deuterated standard even if [D~10~]mesityl oxide was used. Derivatization conditions for GC/MS analysis strongly affected the ratio of the monosilylated intramolecular cyclic form and the disilylated linear form of P‐4MSP. The structural changes of P‐4MSP may have a considerable impact on the development of methods of measuring varietal aroma potential.