Präparative Stereochemie

Velluz, L; Valls, J.; Mathieu, Joachim

doi:10.1002/ange.19670791706

Cited by 18 publications

(4 citation statements)

References 87 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A stereospecific ketonization could either be mediated by the enzyme or it could be due to a stereoelectronic effect of the carbonyl group [ll] and/or asymmetric induction [9] through the chiral centre at C-2.…”

Section: Discussionmentioning

confidence: 99%

Stereochemistry of the Enzymatic Cyclisation of 4,2',4'-Trihydroxychalcone to 7,4'-Dihydroxyflavanone by Isomerases from Mung Bean Seedlings

1970

View full text Add to dashboard Cite

The stereochemistry of the enzyme mediated chalcone-flavanone isomerisation has been investigated. Cyclisation of 4,2',4'-trihydroxychalcone catalysed by either one of the two chalconeflavanone isomerases isolated from mung bean seedlings (Phaseolus aureus Roxb.) leads to the (-)(2 5)-7,4'-dihydroxyfiavanone.When 4,2',4'-[a-2H]trihydroxychalcone is the substrate, deuterium is located preferentially in the equatorial position at C-3 of the flavanone as was shown by nuclear magnetic resonance measurements. Conversely, when the cyclisation is carried out in 2H20 with the unlabeled chalcone, deuterium is preferentially located in the axial position at C-3 of the flavanone. The mechanistic implications of these results are discussed. In experiments described in this paper the absolute configuration at (3-2 was determined by circular dichroism measurementswith 7,4'-dihydroxyflavanone which had been obtained with two isomerase enzymes from mung bean seedlings (Phaseolus aureus Roxb.) [3]. We also investigated whether the cyclisation to the 7,4'-dihydroxyflavanone represents a formal cis-or trans-addition to the double bond of the chalcone (I). The idea of this experiment is the following. When a chalcone deuterated at the u-position is cyclised stereospecifically to the flavanone without deuterium exchange, deuterium will appear in either the axial or the equatorial position a t C-3 of the flavanone. Conversely, when the reaction is carried out in 2H20 deuterium must appear in the opposite position at C-3 of the flavanone. METHODS Synthesis of 4,2',4'-[a-2H]Trihydroxycha2cone ( I I I )300 mg of 7,4'-[3-2H]bisbenzyloxyflavanone [6] were dissolved in 8 ml of absolute dioxane and stirred with 5°/0 Na02H in 2H,0 for 3 h a t room temperature. At the end of this time thin layer chromatography (on silica gel with benzene-isopropanol-methanol, 96 : 6 : 1, v/v/v) showed 4,4'-bisbenzyloxy-2'-hydroxychalcone (RF = 0.89) to be the only product. After addition of ether to the reaction mixture alkali was removed by washing with 2H,0 and subsequently with H,O. After removal of ether the dried residue was stirred for 2 h at room temperature with 1 g of BBr, and 30 ml of methylene chloride. The solvent and BBr, were removed in wacuo and H,O was added. The reaction product was extracted with ether and after the ether solution had been washed with water to neutrality, it was applied to 16 sheets of Whatman 3MM and chromatographed with 50°/, methanol. The zone with RF = 0.40 was eluted from the paper with methanol and the chalcone recrystallized from methanol-water. [6] were dissolved in a small amount of methanol and treated for 10 min with 2 N NaOH. After acidification with H,SO,, the solution was extracted with

show abstract

Section: Discussionmentioning

confidence: 99%

Stereochemistry of the Enzymatic Cyclisation of 4,2',4'-Trihydroxychalcone to 7,4'-Dihydroxyflavanone by Isomerases from Mung Bean Seedlings

1970

View full text Add to dashboard Cite

show abstract

“…Cycloartenyl acetate ( 82) is much more susceptible to attack by chromic acid at C-1 1 than at C-1. The 11-ketone ( 83) is obtained in 25 % yield.82 The derived epoxide (84) isomerises to the 12-ketone (85) under mild conditions, in accordance with the remarkable tendency of the cyclopropyl group to stabilize a positive charge a to the ring.…”

Section: Cozhmentioning

confidence: 86%

Chapter 10. Terpenoids and steroids

Turner¹

1967

Annu. Rep. Prog. Chem., Sect. B

View full text Add to dashboard Cite

BIOGENETIC-TYPE syntheses continue to attract attention. Cyclisation of the terminal epoxides of simpler terpenes gives polyclic systems. Of particular interest is the terminal epoxide (1) of geranylgeranyl acetate,' which, on brief treatment with stannic chloride in benzene, gives the tricyclic product (2) with six asymmetric centres all having the stereochemistry of the natural diterpenoids. Mechanisms involving either a concerted cyclisation or a stepwise process via mono-and bi-cyclic carbonium ions are proposed. The non-enzymic cyclisation of squalene 2,3-epoxide leads to the tricyclic compounds (3) and (7; R = c~H ) ( 8 ; R =

show abstract

“…* Selectivity: even though diversity is a goal, one expects to form only a single product from a given set of inputs. [10] Accordingly, an M-CR, as a synthetic route, is the ultimate in maximal convergence. [9] Maximizing atom economy avoids wasteful atom loss from the starting materials.…”

Section: M-crsmentioning

confidence: 99%

Maximizing Synthetic Efficiency: Multi-Component Transformations Lead the Way

Bienaymé¹,

Hulme

Oddon³

et al. 2000

Chem. Eur. J.

1,088

301

View full text Add to dashboard Cite

With the emergence of high-throughput screening in the pharmaceutical industry in the early 1990's, organic chemists were faced with a new challenge: how to prepare large collections of molecules (the libraries) to "feed" the high-throughput screen? The unique exploratory power of some reactions (such as the 40 year-old Ugi four-component condensation) was soon recognized to be extremely valuable to produce libraries in a time- and cost-effective manner. Over the last five years, industrial and academic researchers have made these powerful transformations into one of the most efficient and cost-effective tools for combinatorial and parallel synthesis.

show abstract

Präparative Stereochemie

Cited by 18 publications

References 87 publications

Stereochemistry of the Enzymatic Cyclisation of 4,2',4'-Trihydroxychalcone to 7,4'-Dihydroxyflavanone by Isomerases from Mung Bean Seedlings

Stereochemistry of the Enzymatic Cyclisation of 4,2',4'-Trihydroxychalcone to 7,4'-Dihydroxyflavanone by Isomerases from Mung Bean Seedlings

Chapter 10. Terpenoids and steroids

Maximizing Synthetic Efficiency: Multi-Component Transformations Lead the Way

Contact Info

Product

Resources

About