This document compares the solvent dichloromethane (DCM) to the more eco-friendly solvent 2-methyltetrahydrofuran (2-MeTHF) for use in amino acid incorporation reactions. DCM is classified as hazardous while 2-MeTHF is naturally derived and has good thermal stability. Experiments incorporating amino acids onto Wang resin showed 2-MeTHF had lower racemization levels than DCM. 2-MeTHF is proposed as a safer, more sustainable alternative to DCM for these reactions.

1. Eco-friendly solvent for
1st Amino Acid Incorporation on Wang
Resin:
2-Methyltetrahydrofuran
(2-MeTHF)
Othman Al Musaimi
1

2. Dichloromethane (DCM)
Classified as a highly
hazardous chemical.
Low boiling point 40⁰C.
Occupational Safety and
Health Administration
(OSHA) as well as US
Environmental Protection
Agency (EPA) consider
methylene chloride to be
a potential
occupational carcinogen.
Its alert level has
escalated by EPA, and
reached the prohibition
level 2
EPA is proposing to prohibit the manufacture (including import),
processing, and distribution in commerce of methylene chloride for
consumer and most types of commercial paint and coating removal
under section 6 of the Toxic Substances Control Act (TSCA).

3. 3
2-MeTHF
2-MeTHF is a naturally
derived substance from
(corncobs or bagasse).
High boiling point (82⁰C).
Good thermal stability.
Considerable stability
under acidic conditions.
Peroxides upon exposure
to oxygen, butylated
hydroxytoluene (BHT) (as
low as 50 ppm).

4. Experimental
Amino Acid Incorporation
1. Known amount of Wang resin is swelled in the corresponding solvent (in an ice bath) for 10-20 min.
2. 5 equivalents (with respect to resin) of each amino acid were weighed and dissolved in a minimum amount of the
solvent and sonicated for 10 minutes then placed in an ice bath for 10 min.
3. 0.25 equivalents of DMAP were added to the previously swelled resin, then the amino acid solution was added to the
(resin + DMAP).
4. 2.5 equivalents of N,N-diisopropylcarbodiimide (DIC) were added.
5. The resulting mixture was allowed to react (under mechanical shaking) for 2 hrs at 0⁰C plus 2 hrs at RT.
6. The resin was washed with 2X DMF, then a capping solution consists of acetic anhydride and DIEA (10:20) equivalents
were added to endcap any unreacted amine groups of the Wang resin. Finally, the resin was washed with 2X DMF and 2X
DCM and dried over vacuum.
4
+ DIC

5. 5
Dipeptide Racemization %
(2-MeTHF)
1 Hr RT (Standard) 2,2
H-L-Phe-L-Ser-OH
Methodology Optimization
1 Hr 0⁰C + 1 Hr RT 0,2
2 Hrs 0⁰C + 2 Hrs RT 0,2

6. Loading
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7. Racemization degree determination
H-L-Phe-L-Ser-OH
H-L-Phe-L-His-OH
H-L-Phe-L-Cys-(Acm)-OH
H-L-Phe-L-Leu-OH
H-L-Ser-L-Phe-OH
H-L-Phe-D-Ser-OH
H-L-Phe-D-His-OH
H-L-Phe-D-Cys-(Acm)-OH
H-L-Phe-D-Leu-OH
H-L-Ser-D-Phe-OH
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8. Racemization degree
Solvent Ser Racemization His RacemizationCys(Acm) RacemizationPhe Racemization Leu Racemization
DCM 0.20 5.50 1.30 0.30 0.20
2MeTHF 0.20 1.20 1.10 0.20 0.10

9. Dipeptide formation determination
Dipeptide Fmoc-Gly-OH %
(2-MeTHF)
Fmoc-Gly-OH %
(GVL)
Fmoc-Gly-OH %
(DCM)
Fmoc-Gly-Gly-OH 0.1 0.1 0.1
AAFmoc
AAAAFmoc
9

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neutral, acidic, and basic conditions. Structural Chemistry. 2016; 28: 423-429, 10.1007/s11224-016-0887-6.
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chemicals. Green Chem. 2008; 10: 238-242, 10.1039/b712863k.
6. D. M. Alonso, S. G. Wettstein, J. A. Dumesic, Gamma-valerolactone, a sustainable platform molecule derived from lignocellulosic
biomass. Green Chemistry. 2013; 15: 584, 10.1039/c3gc37065h.
7. E. P. A. (EPA), Regulation of Certain Uses under Toxic Substances Control Act: Methylene Chloride and N-Methylpyrrolidone.
2017, https://www.regulations.gov/document?D=EPA-HQ-OPPT-2016-0231-0001
8. R. Bruckner, Advanced Organic Chemistry: Reaction Mechanisms. 2001: Elsevier Science,
https://books.google.co.za/books?id=1nT6c3TQL8wC
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