Development of a Liquid-Phase Process for Recycling Resolving Agents within Diastereomeric Resolutions

Abstract Image

Development of a Liquid-Phase Process for Recycling Resolving Agents within Diastereomeric Resolutions

Frederico Castelo Ferreira et al

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Org. Process Res. Dev. 10, 784-793 (2006)

http://pubs.acs.org/doi/abs/10.1021/op0600456?prevSearch=enantiomer%2Brecycling&searchHistoryKey=

This paper describes a liquid-phase process for recycling of resolving agents used in the diastereomeric resolution of chiral bases. The process is applicable to the resolution of any chiral base by an organic acid resolving agent which takes place in a polar solvent. The resolving agent is first of all separated from the diastereomeric complex by addition of aqueous HCl. The initial stage of process development is selection of a water-immiscible extracting organic solvent to recover the resolving agent from the resulting acidic aqueous solution. Either distillation or organic solvent nanofiltration is subsequently used to exchange the resolving agent from the extracting organic solvent back into the polar resolution solvent. This choice between these two technologies for solvent exchange depends on the relative boiling points of the two solvents. The resolution of PPI2, a racemic amine by di-p-toluoyl-l-tartaric acid (DTTA), was selected as an example of a typical resolution used in an organic process. Using the conventional process, this resolution requires 1.75 mol equiv of DTTA for each mole of racemic base fed to resolution, and thus the bulk of the DTTA ends up in the mother liquor. Using the recycling process, DTTA from both mother liquor and crystals was recovered and recycled over seven consecutive resolutions, while the final product enantiomeric excess and resolution yield were maintained at 100% and 40%, respectively. In this way the DTTA requirement was decreased from 1.75 to 0.26 DTTA mol equiv, reducing the amount of fresh resolving agent needed for each resolution by 85%.

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Buckminsterfullerene Synthesis

Buckminsterfullerene (or buckyball) is a spherical fullerene molecule with the formula C60. It has a cage-like fused-ring structure (Truncated icosahedron) which resembles asoccer ball, made of twenty hexagons and twelve pentagons, with a carbon atom at each vertex of each polygon and a bond along each polygon edge.

Reference :

Science 2002295, 1500. (10.1126/science.1068427)

http://www.slideshare.net/anthonycrasto64/anthony-crasto-buckyball

SEQUENCE IS AS FOLLOWS

Chemical structure

Mg, MeCHO

U+2192.svg

Et2O
97 %
Grignard Reaction

Chemical structure

PBr3

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PhH
86 % bromination

Chemical structure

Ph3P

U+2192.svg

Chemical structure + Chemical structure

LiOEt

U+2192.svg

EtOH, CH2Cl2
71 % (2 steps)
Wittig Reaction

Chemical structure

I2, Propylene oxide

U+2192.svg

Cyclohexane
92 %

Chemical structure

NBS, Bz2O2

U+2192.svg

CCl4
Wohl-Ziegler Reaction

Chemical structure

KCN, n-Bu4N+ HSO4

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CH2Cl2, H2O
93 % (2 steps)

Chemical structure

KOH

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Ethylene Glycol

Chemical structure

SOCl2

U+2192.svg

Chemical structure

AlCl3

U+2192.svg

CH2Cl2
51 % (3 steps)
Friedel-Crafts Acylation

Chemical structure

TiCl4

U+2192.svg

o-Dichlorobenzene
85 %Aldol Condensation

Chemical structure

FVP

U+2192.svg

1100 °C, 0.1-1.0 %

Chemical structure

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HYDROXYL GROUP PROTECTION BY PNB

MECHANISM

REACTION

wt/vol

MW

moles

density

equivs.

yield

I

0.091 g

386.71

0.0002

1.0

II

0.059 g

167.12

0.0004

1.5

III

0.064 g

206.33

0.0003

1.3

IV

0.007 g

122.17

0.0001

0.2

V

5.0 mL

VI

0.122 g

535.81

0.0002

(97%)

 

Procedure:  25 mL 1-neck flask, stirbar, septum, N2 inlet

Dissolved 0.059 g II, 0.064 g of DCC and 0.007 g of DMAP in 4.0 mL of dry CH2Cl2.  Stirred at rt.  Added a solution of 0.091 g of alcohol I in 1.0 mL of CH2Cl2.  Stirred for 45 min.  The reaction mixture was then concentrated by rotary evaporation to ~ 0.5 mL.  The product was isolated by flash chromatography on silica gel using 10:90 EtOAc-hexanes as eluant.  The product was a clear, colorless oil.

 

1H NMR (CDCl3, 300 MHz) d 8.29 (d, J = 8.4 Hz, ArH), 8.20 (d, J = 8.4 Hz, ArH), 5.97 (dd, J = 15.8, 5.1 Hz, H3), 5.86 (dt, J = 15.8, 5.5 Hz, H2), 5.58 (dq, J= 15.4, 6.2 Hz, H7), 5.41 (dd, J = 15.4, 7.0 Hz, H6), 4.86 (d, J = 5.5 Hz, H1), 3.95 (dd(apparent t), J = 5.9 Hz, H4), 3.85 (dd(apparent t), J = 6.6 Hz, H5), 1.68 (d, J = 6.2 Hz, H8), 0.87 (s, SiC(CH3)3), 0.85 (s, SiC(CH3)3), 0.02 (s, SiCH3), 0.00 (s, Si(CH )2), -0.01 (s, SiCH3).

ARTEMISININ

ARTEMISININ, PRESENTATION

http://www.slideshare.net/anthonycrasto64/anthony-melvin-crasto-presents-artemisinin-11174931

Artemisinin is a photochemical reaction with singlet oxygen forming a hydroperoxide using teraphenylporphyrin asphotosensitizer followed by an ene reaction. This step is then followed by a thermal Hock rearrangement initiated by trifluoroacetic acid. Another round of oxygen adds another hydroperoxide unit and another rearrangement forms artemisinin itself. This sequence takes place in a continuous flow reactor and in the photochemical step all the tubing is wrapped around the lamp for maximum exposure to light.

artemisinin seeberger

Francois Levesque and Peter Seeberger laid out their plans for scaling up the production of the important anti-malarial drug artemisinin (DOI). Their vision: the industrial production from dihydroartemisinic acid in a single continuous flow reaction

Synthesis of Cyclic Peptides by Amide Bond Rearrangement

thumbnail image: Synthesis of Cyclic Peptides by Amide Bond Rearrangement

Derek Macmillan and colleagues, University College London, UK, report a simple new route to cyclic peptides from unactivated linear precursors. In the presence of a thiol, an N→S acyl shift in linear peptides can give thioesters, key components for native chemical ligation (NCL). These transient C-terminal thioesters can be intercepted by an N-terminal cysteine to form a new amide bond through NCL and result in biologically active cyclic products.

The products are of considerable interest because peptide cyclization is known to increase the therapeutic potential of many peptides by increasing their thermal and proteolytic stability as well as oral bioavailability.

Synthesis of Cyclic Peptides through an Intramolecular Amide Bond Rearrangement
D. Macmillan, M. De Cecco, N. L. Reynolds, L. F. A. Santos, P. E. Barran, J. R. Dorin,
ChemBioChem 2011.
DOI: 10.1002/cbic.201100364

volleyball

DR ANTHONY CRASTO