Pungent compounds. Part I. An improved synthesis of the paradols (alkyl 4-hydroxy-3-methoxyphenethyl ketones) and an assessment of their pungency

Abstract

Eleven members of the homologous series of paradols, of which one, [6] paradol (n-heptyl 4-hydroxy-3-rnethoxyphenethyl ketone), occurs naturally in the seeds of Amomum melegueta Roscoe (Zingiberaceae) (otherwise known as Grains of Paradise, Guinea pepper, or Melegueta pepper), have been synthesised by an improved method. Physical characteristics, including g.1.c. behaviour, and pungency evaluation experiments are described for the series.THE paradols 1 ~2 are a series of phenolic ketones of general formula (1), structurally related to the gingerols (2) and the shogaols (6).3 Representatives of all three types of molecule have been identified l s 3 as pungent principles in the oleoresin of commercial extracts of ginger, prepared from the rhizomes of the tropical plant Ziizgiber oflcinale Roscoe (Zingiberaceae) ; [6]gingerol (3) and [6]paradol (13) have been found in the seeds of Amomum melegueta Roscoe (Zingiberaceae) , variously known as Grains of Paradise, Guinea pepper, or Melegueta pepper .4t The number bracketed before the name designates the number of carbon atoms in the aldehyde which would be produced by a retro-aldol reaction on the gingerol (2). Thus each gingerol (2) is identified by the length of this potentially aldehydic portion of the side chain. To ensure consistency, the same nomenclature has been adopted to cover the shogaols (6) and the paradols ( l ) , though it is recognised that the latter cannot undergo retro-aldol fission.$ B. P. Appl. 45379/1972.

First Total Synthesis of Cytotoxic Diarylheptanoids, Galeon, and Pterocarine

“…[34,35] The cross-aldol condensation of 2 with acetone in the presence of 10% NaOH gave 3 in 93% yield, whereas such condensation of unprotected 4-hydroxy-3-methoxy-cinnamaldehyde led to much a lower yield. Catalytic hydrogenation of 3 under an H 2 atmosphere at room temperature for 24 h not only the reduced double bonds but also removed the protecting benzyl group to afford the corresponding 4 in quantitative yield, which was then subjected to a second aldol condensation reaction with 3-bromo-4-benzyloxybenzaldehyde to give the linear diphenylheptenoid 5 in 85% yield.…”

Evaluation of spices and oleoresin‐VI‐pungency of ginger components, gingerols and shogoals and quality

“…These non-pungent compounds have similar ultra-violet and infrared spectra as gingerols and shogaols (unpublished observations). These may be the homologues with longer side chains (lo)-, (12)-reported to have higher Rf in TLC (Connell & McLachlan, 1972) or the gingediols and gingediacetate which have recently been reported by the Japanese group (Murata, Shinohara & Miyamoto, 1972;Masada et al, 1974). Connell(l970) or Masada et al (1974) do not record if the gingerols having shorter or longer side chains differ in intensity of pungency or have any pungency.…”

“…These may be the homologues with longer side chains (lo)-, (12)-reported to have higher Rf in TLC (Connell & McLachlan, 1972) or the gingediols and gingediacetate which have recently been reported by the Japanese group (Murata, Shinohara & Miyamoto, 1972;Masada et al, 1974). Connell(l970) or Masada et al (1974) do not record if the gingerols having shorter or longer side chains differ in intensity of pungency or have any pungency. However in line with the observations on synthetic analogs of capsaicin (Nelson, 19 19), and the paradols (Locksley, Rainey & Rohan, 1972), it could be expected that highest pungency is noted in the dominant natural product, the (6)-ginger01 and (6)-shogaol and other analogs with shorter and longer side chains have lower or no pungency.…”

Pungency: The Stimuli and Their Evaluation

“…Their contribution to pungency is not known, but in view of the relation of pungency to chain length established in the case of the capsaicin (10,24) and paradol (46) series, minor amounts of these lower and higher homologs would not be expected to contribute significantly to pungency.…”