Automated synthesis instrumentation

In the DoE approach, first process variables are screened to determine which are important to the outcome (excipient type, percentage, mixture time, etc.). The next step is optimization, when the best settings for the important variables are determined. In particular, response surface methodologies have been successfully applied in both drug discovery and development [33]. Advances in supporting software, automated synthesis instrumentation, and high-throughput analytical techniques have led to the broader adoption of this approach in pharmaceutical discovery and chemical development laboratories [34],... 

RB Merrifield, JM Stewart, N Jemberg. Instrument for automated synthesis of peptides. Anal Chem 38, 1905, 1966. 

A 48-membered library of 2-arylbenzoxazoles has been prepared by the condensation of substituted 2-aminophenols with a series of acid chlorides. The reactions proceeded in the absence of a base in sealed tubes in an automated microwave instrument, which used sequential rather than parallel reaction processing. Comparisons to the conventional thermal conditions demonstrated the importance of the high temperatures and pressures achieved under microwave heating, which ensured that the reactions proceeded efficiently (Scheme 3.16)26. An analogous synthesis ofbenzoxazolesby the cyclocondensation reaction of 2-aminophenols with S-methylisothioamide hydroiodides on silica gel, under microwave irradiation, has also been reported (Scheme 3.16)27. 

The instrument chosen for the evaluation of carbohydrate synthesis was an ABI-433 peptide synthesizer (Fig. 2). The instrument was adapted for carbohydrate synthesis and customized coupling cycles were developed. A specially designed low-temperature reaction vessel was installed and interfaced with a commercially available cooling device.13 The necessary reagents were loaded onto the instrument ports and reaction conditions were programmed on the computer, in a fashion similar to the automated synthesis of peptides. 

Liquid chromatography/mass spectrometry (LC/MS)-based techniques provide unique capabilities for pharmaceutical analysis. LC/MS methods are applicable to a wide range of compounds of pharmaceutical interest, and they feature powerful analytical figures of merit (sensitivity, selectivity, speed of analysis, and cost-effectiveness). These analytical features have continually improved, resulting in easier-to-use and more reliable instruments. These developments coincided with the pharmaceutical industry s focus on describing the collective properties of novel compounds in a rapid, precise, and quantitative way. As a result, the predominant pharmaceutical sample type shifted from nontrace/pure samples to trace mixtures (i.e., protein digests, natural products, automated synthesis, bile, plasma, urine). The results of these developments have been sig-... 

SEQUOS is an automated synthesis tool for drug discovery and process development it is an automated synthesis system which maintains precise control of reaction time, temperature and reactant concentration ratios, which allows syntheses to be conducted on a continuous basis from 50 mg up to the gram scale. By modification of the SEQUOS system it is also possible to produce quickly 100 g or kilogram quantities of target compounds utilizing the same instrument and reaction conditions. This eliminates the time and effort currently required for scale-up [37]. 

High-throughput preparative HPLC coupled to electrospray ionization mass spectrometry (Chapter 17), which disposes upon a signal for collecting detected compounds of the defined molecular mass, is one of the highly promising new developments in this area. Such systems can be incorporated for synthesis purposes into the periphery of automated multicomponent systems, thus making a valuable contribution to the rationalization and quality enhancement of combinatorial synthesis processes. The combination of automated synthesis, purification and on-line instrumental identification (NMR, IR, MS) will become feasible in the near future, and as a matter of routine operation. Analytic methods of structure elucidation will then also be able to be combined with automated combinatorial chemistry. 

Tetrameric peptides syntheses are performed on a Symphony synthesizer (Rainin Instruments, Protein Technologies, Inc. Woburn, MA) by Fmoc solid-phase stepwise peptide synthesis on trilysine core. These instructions are easily adaptable to other automated peptide synthesis instruments. 

Synthesis on solid supports was first developed by Merrifield [1] for the assembly of peptides. It has expanded to include many different applications including oligonucleotide, carbohydrate, and small-molecule assembly (see Chapters 11 and 14). The repetitive cycle of steps involved in the solid-phase synthesis of biopolymers can be performed manually using simple laboratory equipment or fully automated with sophisticated instrumentation. This chapter examines typical solid-phase reaction kinetics to identify factors that can improve the efficiency of both manual and automated synthesis. The hardware and software features of automated solid-phase instruments are also discussed. The focus of this discussion is not on particular commercial model synthesizers but on the basic principles of instrument operation. These considerations can assist in the design, purchase, or use of automated equipment for solid-phase synthesis. Most contrasting features have advantages and disadvantages and the proper choice of instrumentation depends on the synthetic needs of the user. 

Automated synthesis can ran unattended and is less prone to human error than manual synthesis. As the biopolymer assembly process was automated, there was a tendency to produce longer sequences. This, in turn, required better synthetic methods, which has led to continual improvements in solid-phase chemistries and instrument design. 

The goal of an automated peptide synthesis instrument is to produce the purest peptide in a reasonable amount of time with little waste of reagents and solvents. This can be achieved with efficient chemistries and reliable instrument hardware and software. 

Because of the inherent ability of solid-phase synthesis to be integrated and automated, numerous instruments were built from the onset of solid-phase chemistry, and this development culminated after the introduction of combinatorial chemistry methods. Operational simplicity of solid-phase synthesis contributed to the development of multiple solid-phase synthesis, where numerous reaction vessels are handled at the same time. In 1989, Schnorrenberg and Gerhardt" introduced the automated multiple synthesis of peptides in parallel fashion. Multiple synthesis in a continuous flow manner was also later reported. 

Different instruments are now available for automated synthesis on solid phase. The Applied Biosystems peptide synthesizer ABl 433 (Fig. 3) was chosen as an initial platform due to its wide availability and the few modifications necessary for its application to oligosaccharide synthesis. The custom-made reaction vessel is constructed of jacketed glass to allow cooling. The building blocks are placed in cartridges to be delivered sequentially. The synthesizer allows for nine different solvents and reagents. A new, more versatile and less... 

A recent development in this context is the Liberty system introduced by CEM in 2004 (see Fig. 3.25). This instrument is an automated microwave peptide synthesizer, equipped with special vessels, applicable for the unattended synthesis of up to 12 peptides employing 25 different amino acids. This tool offers the first commercially available dedicated reaction vessels for carrying out microwave-assisted solid-phase peptide synthesis. At the time of writing, no published work accomplished with this instrument was available. 

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