Peptide Synthesis made Efficient using Sonication

Solid Phase Peptide Synthesis (SPPS) is the common method for peptide synthesis. Ultrasonication is a reliable tool to intensify solid phase peptide synthesis resulting in higher yields, improved purity, no racemization and significantly accelerated reaction speed. Hielscher Ultrasonics offers various ultrasonic solutions for peptide synthesis, cleavage, and dissolving.

Ultrasonic Peptide Synthesis

Ultrasonication is already widely applied as intensifying method in organic synthesis and is well known for its advantages such as drastically reduced reaction times, higher yields, less by-products, the initiation of pathways, which could not be achieved in other ways, and/or better selectivity. Great benefits can be also obtained, when sonication is coupled into peptide synthesis reactions. Research results have demonstrated that ultrasonically assisted peptide synthesis achieves optimized yield of peptides with high purity, without racemization within a short reaction time.

Graphic demonstrating the Merrifield solid phase peptide synthesis. Ultrasonication is used to promote and enhance the synthesis reaction as well as for cleavage of the synthesized peptides from the resin.
Graphic: ©Conejos-Sanchez et al., 2014)

Solid Phase Peptide Synthesis Improved with Ultrasound

Solid Phase Peptide Synthesis (SPPS) is a chemical reaction that allows the assembly of a peptide chain through successive reactions of amino acid derivatives on an insoluble porous support. However, the traditional solid-phase peptide synthesis is a relatively inefficient and slow process. Therefore, ultrasonic intensification of peptide synthesis is a highly regarded tool for a more efficacious and rapid synthesis of peptides.
Silva et al. (2021) compared “classical” fluorenylmethoxycarbonyl (Fmoc)-solid phase peptide synthesis (SPPS) with ultrasound (US)-assisted SPPS based on the preparation of three peptides, namely the fibroblast growth factor receptor 3(FGFR3)-specific peptide Pep1 (VSPPLTLGQLLS-NH2) and the novel peptides Pep2 (RQMATADEA-NH2) and Pep3 (AAVALLPAVLLALLAPRQMATADEA-NH2).
US-assisted SPPS led to a 14-fold (Pep1) and 4-fold time reduction (Pep2) in peptide assembly compared to the “classical” method. Interestingly, ultrasound-assisted SPPS yielded Pep1 in higher purity (82%) than the “classical” SPPS (73%). The significant time reduction combined with high crude peptide purity attained prompted the research team to apply US-assisted SPPS to the large peptide Pep3, which displays a high number of hydrophobic amino acids and homooligo-sequences. Remarkably, the synthesis of this 25-mer peptide was attained within less than 6 hours (347 min) in moderate purity (approx. 49%).

Faster peptide synthesis via solid phase peptide synthesis using ultrasonic agitation.
(Study and analysis: Wołczański et al., 2019)

Merlino et al. (2019) also conducted a comprehensive study of the ultrasonic effects on Fmoc-based solid-phase peptide synthesis, which allowed for the synthesis of different biologically active peptides (up to 44-mer), with a remarkable savings of material and reaction time. They demonstrated that ultrasoniction did not exacerbate the main side reactions and improved the synthesis of peptides endowed with “difficult sequences”, placing the ultrasonically-promoted solid-phase peptide synthesis (US-SPPS) among the current high-efficient peptide synthetic strategies.

The availability of high-performance systems for the ultrasonic (sonical) synthesis of peptides allows for significantly improved synthesis rates and an increase of the purity of raw products. (cf. Wołczański et al., 2019)

The investigation of racemization. Comparison of significant 1H NMR spectra of models peptides synthesized manually using the classical approach at room temperature vs ultrasonic method at elevated temperature. Chemical shifts of His and Cys α-protons and methylene group of Acm (left panels), ɣ-methyl protons of Val (right panels) show that sonication at 70°C does not cause racemization.
(Study and analysis: Wołczański et al., 2019)

Ultrasonic Cleavage of Peptides

After solid-phase peptide synthesis (SPPS), synthesised peptides must be cleaved from the polymeric resins. This step is also known as deprotection. When common shaking and ultrasonication for peptide cleavage from resin are compared, the shaking method requires approx. 1 hour, whilst ultrasonic cleavage can be accomplished in 15 to 20 min. The ultrasonic peptide cleavage can be applied to the cleavage of protected amino acids and peptides linked to polystyrene resins through benzylic ester bonds.

Ultrasonic cleavage of peptides from polystyrene resin gives high yields of peptides in high purity, without racemization, within a rapid procedure.
(study and graphic: ©Anuradha and Ravindranath, 1995)

Many peptide syntheses are performed in syringes (e.g., fritted syringe reactors). Hielscher’s ultrasonic syringe agitator sonicates the peptide solution coupling the ultrasound waves through the syringe wall into the liquid. The ultrasonic syringe agitator is one of the most popular ultrasonic solutions for the ultrasonically-assisted synthesis of peptides.
The ultrasonic cuphorn is a suitable tool to sonicate up to 5 reactor vessels, whilst the VialTweeter can hold up to ten reaction tubes plus additionally five larger vessel via clamp-on accessory.
For other reactor types such as the Merrifield or Kamysz solid-phase reactor and other polypropylene or borosilicate vessels / reactors, Hielscher offers customized clamp-on ultrasonic systems for indirect sonication.
For solid phase peptide synthesis in multiwell / microtiter plates, the UIP400MTP is the ideal device. Ultrasonic cavitation is indirectly coupled uniformly into the numerous sample wells for superior mass transfer and synthesis reaction. Watch the video below to see the UIP400MTP in action!
Of course, larger strirred glass reactors, e.g. for solution-phase synthesis, can be easily equipped with ultrasonic probes (a.k.a. sonotrodes or ultrasonic horns) of any size.