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Serra S.,CNR Institute of Chemistry of Molecular Recognition
Natural Product Communications | Year: 2012

An expedient and concise synthesis of (S)-trans-γ-monocyclofarnesol is here described. The aforementioned sesquiterpene was prepared starting from enantioenriched (S)-γ-dihydroionone, which was in turn obtained from racemic α-ionone through the combined use of two previously developed processes. Key steps of the presented synthesis are the stereoselective Horner-Wadsworth-Emmons reaction between triethyl phosphonoacetate and γ-dihydroionone and the effective fractional crystallization of the γ-monocyclofarnesol-3,5-dinitrobenzoate esters. By these means the target compound was obtained in good yield and with very high stereoisomeric purity. Source


Serra S.,CNR Institute of Chemistry of Molecular Recognition
Natural Product Communications | Year: 2013

The enantioselective syntheses of both the enantiomeric forms of the four natural tetralones 1a-d are here described. The aforementioned trinorsesquiterpenes were prepared starting either from substituted (S)-3-arylbutanols 5a-c or from substituted (S)-2-arylpropanols 7a-c. The latter chiral building blocks were in turn obtained through two different kinds of enzymatic transformations consisting of the baker's yeast mediated reduction of substituted (E)-3-aryl-but-2-enals 4a-c and the lipase-mediated resolution of racemic 2-arylpropanols 7a-c, respectively. Further key steps of the presented syntheses were C1 and C2 homologation procedures as well as the ring closure of the substituted 4-aryl-pentanoic acids 3a-c. By these means the target compounds were obtained in good yields and with very high stereoisomeric purity. In addition, the trinorsesquiterpene schiffnerone-B was synthesized for the first time and its absolute configuration was unambiguously assigned. Source


Serra S.,CNR Institute of Chemistry of Molecular Recognition
Natural Product Communications | Year: 2012

The enantioselective synthesis of (S)-1-hydroxy-1,3,5-bisabolatrien-10-one 1 is here described. This sesquiterpene was prepared using (S)-3-(2-methoxy-4- methyl-phenyl)butan-1-ol as a chiral building block. Two different pathways were employed and both turned out to be high yielding, affording 1 in good chemical purity and without any racemization of the existing stereocenter. The spectroscopic data of the synthetic (S)-1 were in very good agreement with those reported for the natural compound, which was extracted from Juniperus formosana heartwood and from the leaves of J. chinensis. The positive sign of the measured optical rotation value of synthetic (S)-1 allows the unambiguous assignment of the absolute configuration of (+)-1 as the (S)-enantiomer. This finding corrects the previous configuration determination which indicated the opposite result. At last, since even (R)-3-(2-methoxy-4-methyl-phenyl)butan-1-ol is preparable in high enantiomer purity by mean of a different biocatalytic process, the formal synthesis of natural (R)-1 was also accomplished. Source


Serra S.,CNR Institute of Chemistry of Molecular Recognition
Flavour and Fragrance Journal | Year: 2013

We report the enantioselective synthesis of the ambergris odorants (+)-(S)-γ-ionone, (+)-(S)-γ-dihydroionone, (-)-α-ambrinol, (+)-(S)-γ-coronal, (-)-(S)-γ-homocyclogeranyl chloride and (+)-(S)-γ-homocyclogeraniol. At first, the enantio-enriched (4R,6S)-4-acetoxy-γ-ionone was prepared starting from commercial racemic ionone alpha by means of a chemo-enzymatic process. This chiral building block was then converted into (S)-γ-dihydroionone which was used as the starting material for the synthesis of the aforementioned odorants. © 2012 John Wiley & Sons, Ltd. Source


Serra S.,CNR Institute of Chemistry of Molecular Recognition
Tetrahedron Asymmetry | Year: 2011

A comprehensive study of the lipase-mediated resolution of substituted 2-aryl-propanols is reported. The latter alcohols were submitted to the irreversible acetylation catalyzed either by PPL, CRL, or lipase PS. The enantioselectivity of these transformations was dependent on the type of lipase used. The type of substituents and particularly their position on the aromatic ring strongly affected the selectivity of the reaction. The experiments described prove that PPL is the more versatile lipase catalyzing the acetylation with an enantiomeric ratio (E) value that ranges from 1 up to 144, depending on the substrate used. Conversely, the same transformations were catalyzed by CRL and lipase PS with an enantiomeric ratio value, which is always less than 5. The remarkable behavior of PPL was exploited in the large scale resolution of some substituted 2-aryl-propanols whose enantiomeric forms are relevant building blocks in the enantioselective synthesis of phenolic sesquiterpenes. By these means, the synthesis of (S)-turmeronol B and the formal syntheses of (R)-curcumene, (R)-curcuphenol, (R)-xanthorrhizol, and (R)-curcuhydroquinone were accomplished. © 2011 Elsevier Ltd. All rights reserved. Source

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