Lignans dibenzylbutyrolactone

However, the enantiomeric control by DPs does not lead to the production of optically pure pinoresinol in plants, because the enantiomeric compositions of pinoresinol from various plant species vary widely and optically pure pinoresinol has not yet been isolated from plants [11,13, 53]. Downstream lignans in the lignan biosynthetic pathway, such as dibenzylbutyrolactone lignans including matairesinol, are optically pure [11, 13, 53]. These facts unequivocally indicate that not only was... 

Some approaches to the stereoselective synthesis of a-hydroxylated lactone lignans have been reported [59,60]. As a short and efficient example, the synthesis of a dibenzylbutyrolactone lignan wikstromol from two diastereo-selective alkylations of malic acid (+) has recently been reported [61]. In order to get high stereoselectivity, isoPr malate was chosen for the synthesis of (+)-wikstromol its formation in six steps with a 20% overall yield is shown in Fig. 10. 

The dibenzylbutyrolactone lignan matairesinol was also found to be an anti-HIV agent [110], although the sample used in this bioassay was not isolated from a Taxus species. Another dibenzylbutyrolactone lignan, arctigenin, as well as its unsubstituted benzyl derivative exhibited anti-HIV replication activity, with EC50 values of 0.16 and 22 ig/mL and therapeutic index values of 5 and 9.1, respectively [111]. 

Kamil, W.M. and Dewick, P.M. (1986b) Biosynthetic relationship of aryltetralin lactone lignans to dibenzylbutyrolactone lignans. Phytochemistry, 25, 2093 102. 

Chenevert synthesized both enantiomers of a dibenzylbutyrolactone lignan using as key step an enzymatic desymmetrization reaction of meso alcohols, Scheme (43) [110]. 

Dao L, Friedman M (1992) Chlorogenic acid content of fresh and processed potatoes determined by ultraviolet spectrophotometry. J Agric Food Chem 40 2152-2156 De A. Lima OO, Braz-Filho R (1997) Dibenzylbutyrolactone lignans and coumarins from Ipomoea cairica. J Braz Chem Soc 8 235-238... 

The lignans are a large group of plant phenolics, biosynthesized from the union of two phenylpropane molecules e.g., both matairesinol (Centaurea species, family Asteraceae) and podophyllotoxin Podophyllum peltatum, family Berberidaceae) are formed from the phenylpropane coniferyl alcohol. Lignans are essentially cinnamoyl alcohol dimers, though further cyclization and other structural modifications result in various structural types, e.g. dibenzylbutyrolactone and epoxy lignan. 

Treatment of dibenzylbutyrolactone 24 with [bis(trifluoroacetoxy)iodo]benzene in trifluoroethanol for one hour gives as the major product spirodienone 25, which has been postulated as an intermediate in the biosynthesis of tetrahy-drodibenzocyclooctene lignans [26] (Scheme 11). 

Analogously, Pelter and co-workers reported that PIFA reacts in CF3CH2OH with readily available rans-2,3-dibenzylbutyrolactones (150) to produce isoste-ganes (32) and steganes (33) (Scheme 22). After that, they improved the yields of 32 and 33 by treating 150 with PIFA in aqueous MeOH followed by treatment with TFA via the quinol intermediate 151 [108]. Related synthetic studies toward lignans have also been performed by the same group [109-111]. 

The stegane lignans are thought to originate biogenetically from the same pathway as the podophyllotoxin lignans, a common precursor being the dibenzylbutyrolactone yatein, Fig. (6) [35]. 

Another Cyclization Reaction of 2,3-Dibenzylbutyrolactone Type Lignan to... 

As the previous chapters have demonstrated, chiral auxiliaries have found a widespread application in the asymmetric synthesis of lignans. Among them, chiral oxazolidinones have been used extensively due to their ability to produce excellent diastereoselectivities in aldol as well as in numerous other reactions. For example, Kise et al. reported the use of (5)-4-isopropyl-3-(phenylacetyl)-2-oxazolidinone (141) in oxidative homocoupling reactions and its application in the asymmetric synthesis of dibenzylbutyrolactones and dibenzylbutandiols, Scheme (26) [86,87]. Treatment of 3-arylpropanoic acid derivative 142 with LDA in the presence of TiCU yielded a mixture of the dimeric compounds 143 in a ratio of 85 15 to 87 13. The major product having (R,R) configuration was converted into dibenzylbutyrolactones 145 in a three step sequence... 

Dibenzocyclooctene lignans. The skeleton of these natural products is rapidly formed in high yields by the direct oxidation of phenolic dibenzylbutyrolactones. The oxidation process is biomimetic, although the reagent is not. 

A third route to rra 5-2,3-dibenzylbutyrolactones involves oxidative dimerisation of the dianion of a dihydrocirmamic acid (scheme 7) [51,52]. Reduction of the anhydride to the lactone completes the sequence. This approach, which is ideally suited to the preparation of symmetrically substituted lignans, has also been extended to the preparation of unsymmetrically substituted compounds [53]. This is achieved by reacting an a-iodocarboxylate anion with an appropriate carboxamide dianion or carboxylic acid dianion. 

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