2.2 Synthetic procedure
Iso-oleoyl chloride. As shown in Figure 2 ,iso -oleic acid (5 g, 0.017 mol) in 10 mL of dichloromethane was
added to in a three-neck round bottom flask equipped with a condenser.
The mixture was placed in an ice bath to chill for a couple minutes;
thionyl chloride (2.8 mL, 2.2 equiv.) was then added dropwise viaa syringe. The reaction was heated to reflux at 75 oC
for 2.0 h. When the reaction was completed and cooled, the residual
thionyl chloride and dichloromethane were removed through a vacuum line.Iso -oleoyl chloride was obtained as a viscous yellowish liquid
and was used in a subsequent reaction without further purification.
Ethyl iso-oleoyl arginate hydrochloride. L-arginine ethyl
hydrochloride (3.7 g, 1.0 equiv. toiso -oleoyl chloride) in 30
mL of anhydrous DMF was added to a 50 mL flask with a side arm attached
to the nitrogen line, followed by triethylamine (5.6 mL, 3.0 equiv. to
iso-oleoyl chloride). DMF was treated with activated molecular sieves
for 24 h before use. The iso -oleoyl chloride (4.0 g, 0.013 mol)
was then added to the flask dropwise via an additional funnel.
The flask was capped, stirred at room temperature for 15 minutes, and
then heated at 50 oC for 2 h. The mixture was
dissolved in ethyl acetate and transferred to a separatory funnel. The
organic phase was neutralized with saturated sodium bicarbonate solution
and then washed with water twice. The product was obtained by removing
the organic solvent using rotary evaporator. It was then passed through
a 50 mL SPE column using ethyl acetate:methanol eluent with the
following gradients (9:1, 8:2, 7:3, 6:4, 3:7) to give the desired ethyliso -oleoyl arginate as a viscous light brown product at 76%
yield (Fig. 2, structure 1 ). ATR-FT-IR of the fractionated
products spectroscopic data are provided in SFigure 1
(Supplementary Information) and Figures 3&4 .
Ethyl iso-stearoyl arginate hydrochloride. Ethyliso -oleoyl arginate (Fig. 2, structure 1) was converted
to ethyl iso -stearoyl arginate hydrochloride (Fig. 2,
structure 2) through a general hydrogenation step which can be found in
Ngo et al . (2012). Briefly, in a 4-dram glass vial, ethyliso -oleoyl arginate hydrochloride, 1 (200 mg, 0.43 mmol)
was dissolved in 5 mL of methanol, added by 5 wt% Pd/C (150 mg). The
vial was sealed with a septum cap having a small hole on it. The hole
was to allow the hydrogen gas to enter the reaction mixture. The vial
was then placed in a 300 mL stainless steel parr reactor where it was
sealed, purged with 50 psi of hydrogen gas and reacted for 24 h (3 h for
the ethyl n -oleoyl arginate) at RT. After the reaction, the
suspension was vacuum filtered through a celite packed funnel to remove
the Pd/C. The methanol was evaporated in a rotary evaporator to give the
desired ethyl iso -stearoyl arginate at >99% yield.
The same synthetic procedure was applied to obtain ethyl n -oleoyl
arginate (Fig. 2, structure 3 ) and ethyl n -stearate
arginate (Fig. 2, structure 4 ). Some intermediate and final
products spectroscopic data are provided in SFigure 1
(Supplementary Information) and Figures 3&4 . From these
experimental results, we can generalize that this two-step process is
universal and can be applied to other types of fatty acid feedstocks.
Lauroyl chloride. As shown in Figure 2 , fatty acid such
as lauric acid (2.5 g, 0.012 mol) was dissolved in 30 mL of
dichloromethane and transferred in a three-neck round bottom flask
equipped with a condenser. The mixture was placed in an ice bath to
chill for a couple minutes, thionyl chloride (2.0 mL, 2.2 equiv.) was
then added dropwise via a syringe. The reaction was heated to
reflux at 75 oC for 3.0 h. When the reaction was
completed and cooled, the residual thionyl chloride and dichloromethane
were removed through a vacuum line. Lauroyl chloride was obtained as a
viscous yellowish liquid and was used in a subsequent reaction without
further purification (Fig. 2 ).
Ethyl lauroyl arginate. L-arginine ethyl hydrochloride (2.3 g,
1.0 equiv. to lauric acid chloride) was dissolved in 15.0 mL of
anhydrous DMF. The L-arginine solution was then transferred into a flask
attached to a side arm with triethylamine (2.5 mL, 3.0 equiv. to lauric
acid chloride) slowly added to it. The lauroyl chloride (1.8 g, 0.0082
mol) was added to the solution dropwise via an dropping funnel.
The flask was capped, stirred at room temperature for 15 minutes and
then heated at 50 oC for 2 h. The product was
extracted with solvent and washed with water. It was then passed through
a short silica gel column using an eluent of 1:1 methanol:ethyl acetate
solution to give the desired pure ethyl lauroyl arginate (5) as
a white solid product at 91% yield.