Total synthesis automated

This method presents several advantages it is fast (20 min total synthesis time), efficient, clean and readily automated. A high specific radioactivity (20-25 GBq pmol starting from 10 - 50 MBq of [ F]fluoride) is obtained for mod-... 

In 2006, Ley reported the application of a continuous flow-through platform for the preparation of the neolignan natural product Grossamide (Scheme 8.48) [63], This was the first report of the enantioselective total synthesis of Grossamide utilizing a fully automated and scalable flow reactor with supported-reagents and scavengers. This principle has a wider impact on multiple step assembly of libraries and natural products. 

Scheme 8.48 Total synthesis of Grossamide utilizing a fully automated reactor with supported reagents and scavengers.

The first successful efforts in enzyme total synthesis involved ribonuclease in the late 1960s and were disclosed in simultaneous publications by Merrifield and Gutte at the Rockefeller [200] and Denkwalter and co-workers at Merck [45, 46, 201-203]. The Rockefeller group s bovine ribonuclease A (RNase A) synthesis utilized automated, stepwise Boc/Bzl chemistry to assemble the 124 amino acid sequence. Following conversion to the S-sulfonate derivative and purification by ion-exchange and gel chromatography, the material was reduced to the firee sulf-hydryl form and air oxidized to form the four disulfide bonds. Upon further purification the protein was shown to be identical to the native enzyme by paper... 

The first enantioselective total synthesis of the 2-aryl-2,3-dihydro-3-benzofuran-carboxyamide neolignan grossamide was also developed using a fully automated and scalable fiow reactor [39]. 

Several different synthesis routes of paclitaxel have been published. The total synthesis has been first achieved independently by two teams in 1994, the Holton s and the Nicolaou s [41-43]. The third synthetic route was accomplished by Danishefsky s group in 1996 [44]. Total synthesis of Taxol is a complex task for chemists given the fact that the molecule consists of four complicated rings (A, B, C rings and the oxetane ring) and has 11 chiral centers. The synthesis processed more than 20 steps, and only 0.07% and 2.7% production rates for the Holton s and Nicolaou s routes were obtained, respectively [41, 42]. Mukaiyama et al. have proposed an improved method for the asymmetric total synthesis of Taxol by a different way [45]. An automated synthesizer with a 36-step synthesis sequences for intermediate of Taxol was developed by Doi et al. (2006) [46]. Due to the complexity of Taxol structure, the expensive chemical reagents, and the strict requirement for reaction, the process of the total synthesis of Taxol is multiple-step, costly, and commercially unfeasible for industrial application for Taxol manufacture. 

Doi T, Euse S, Miyamoto S, Nakai K, Sasuga D, Takahashi T (2006) A formal total synthesis of taxol aided by an automated synthesizer. Chem Asian J 1 370-383. doi 10.1002/ asia.200600156... 

Obviously, it is not necessary to stop at the dipeptide stage. Repetition of the deprotection-coupling sequence leads to larger and larger peptides. Merrifield designed a machine that would carry out the required series of manipulations automatically, each cycle requiring only a few hours. In this way, the first total synthesis of the protein insulin was accomplished. More than 5000 separate operations were required to assemble the 51 amino acids in the two separate chains thanks to the automated procedure, this took only several days. 

Peptide chemistry has made headlines this year with the publication of the first total synthesis of an enzyme. Ribonuclease A, a peptide or rather protein with 124 amino acid residues was prepared by two independent groups and by two quite different procedures, the now well-established Merrifield automated solid-state synthesis and a fragment condensation method with 19 preassembled parts. Regarding the Merrifield method, improved attachment and removal of the polymeric peptide support have been reported. A new peptide synthesis proceeds through sulfen-amides by an oxidation-reduction process . Peptides can also be obtained from N-protected aminothiolic aryl esters and sulfen-amino acids with selective removal of a protective o-nitrophenyl-sulfenyl group... 

The first total synthesis of an enzyme, ribonuclease A, was reported in 1969 [7]. In this work, accomplished almost simultaneously by research groups at Rockefeller University and at Merck and Company, 19 amino acids were assembled into the protein that has 124 units in a definite sequence (Figure 15.2). In one technique, each amino acid was added in sequence after the first, valine, was fully bound to an insoluble substrate. To do this, 369 chemical reactions requiring 11,931 steps were carried out in an automated apparatus. A three-dimensional picture of the enzyme illustrates the formation of helical and sheetlike portions (Figure 15.3). Much can be learned about protein behavior and conformation by studying simpler molecules, such as synthetic polypeptides, which are polymers of a single a-amino acid. 

Will this allow syntheses to be automated It depends how difficult syntheses are (and will provide a way of quantifying this). It may be that the best possible synthesis is not required, provided that a good route is available, as assessed by total cost (including waste disposal and safety precautions), by time required, by certainty of success, by ease of using robots to follow the procedure, and so on. 

These are total systems or even plants made for parallel automated organic synthesis, typically in the liquid phase. In this section, no commercial devices (typically not relying on micro flow processing) are considered, but rather only specialty apparatus developed in the framework of chemical micro processing. 

Nucleotides and nucleic acids are critical tools in the areas of gene expression, therapeutics, and diagnostics. However, there are certain challenges associated with their large-scale purification and subsequent characterization. While solid-state oligonucleotide synthesis is relatively simple and can be totally automated, intra- and intermolecular associations may occur involving shorter sequences that may hybridize with the desired full length... 

Several chalcone-based libraries (see Fig. 4.11, section 4.2.2) were combined to give a total of over 74,000 discretes (82) and, while no mention of time and resources required was made in the paper, the significant effort required to develop the automated equipment for the synthesis of medium-large libraries in solution in-house was surely paid back by the potential to continuously produce primary lead-seeking libraries in solution in large quantities. Only a few specialized companies may invest so heavily in combinatorial automation, but any interested party can access these companies to contract a library synthesis starting from a proprietary chemistry of interest. 

Liquid-liquid two-phase extractions are sometimes suitable for parallel synthesis. Manual multichannel pipettes can handle a few tens of solutions and recover the desired liquid phase after the extraction. If numbers of individuals increase, partial or total automation is necessary and mono- or multichannel robotic pipettes deliver solutions and withdraw either the top or the bottom phase of a liquid-liquid system with extreme accuracy, transferring it to other reaction vessels. They allow the sequential preparation of medium-large libraries but are very time consuming when large libraries of > 1000 members are involved. 

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