Recent research finding

No.33 Physical properties of R(+) alpha Lipoic acid by Complexation with γ-Cyclodextrin


Continued from No.21_RALA-CD Alpha Lipoic acid γcyclodextrin complex

What is alpha Lipoic acid?

Alpha Lipoic acid exists in nature and is an essential cofactore of mitochondrial enzyme complexes. Glucose taken into cells is changed into pyruvic acid by glycolytic pathway. Pyruvic acid is changed into acetyl CoA by pyruvate dehydrogenase complex (PDC), then acetyl CoA is oxidized at TCA cycle and electron transfer system followed by generation of ATP. Lipoic acid is essential for PDC and glucose metabolism. Continuous high blood glucose level causes generation of advanced glycation end products (AGEs). It is explained that AGEs cause the complications of diabetes mellitus and aging. Alpha Lipoic acid which can works for conversion from glucose to energy is now very popular as anti glycation materials.

Energy generation from Glucose and ALA


The carbon atom at C6 of Alpha Lipolic acid is chiral and the molecule exists an two enantiomers R-(+)-Lipoic acid (RALA) and S-(-)-lipoic acid (SALA). Only the RALA exists in nature and is an essential cofactor of four mitochondrial enzyme complexes. Since RALA (mp. 46-49℃) is unstable compound, it is easily decomposed and generates sticky insoluble polymer. Therefore, RALA has not been commercially available, but only racemic compound (mp. 60-62℃).
RALA-CD inclusion complexes were prepared, and their stability against heat and acid conditions were evaluated.

RALA-CD complex

* CD complexation procedure has been applied to patent and NOT disclosed. (JP2010-172420)

Analysis of RALA by HPLC

Unit Integrated HPLC System LC-2010C (Shimadzu)
Column CHIRALPAK AD-RH (Daicel) (4.6 mm I.D. x 150 mm)
Flow and temp. 0.6 mL/min, 25℃
Mobile phase 25mM H3PO4:CH3CN=70:30
Detector UV 215 nm
Injection volume 10μL
Retention time 35min (SALA), 38min (RALA)


Efficiency of complexation process


RALA contents in RALA-CD complexes which were made by mixing RALA and CD (1:1 mol ratio) were analyzed by HPLC.

RALA (theoretical) 15.6% 13.7% 12.3%
RALA (analyzed) 11.7% 13.2% 11.9%
Yield* 75.5% 96.6% 96.7%

* Yield (%) = RALA (analyzed) /RALA (theoretical)

Stabilizing effect of CDs on RALA

Residual ratio of RALA under heated condition

(Light shielding, 70℃, saturated humidity, 2h)

Each samples were treated under the test conditions (light shielding, 70℃ and saturated humidity) for 2 hours, then residual RALA content was analyzed. The results were shown as residual ratio of RALA against initial value.

Evaluation of RALA-γCD complex

Stability of RALA in water condition

RALA contents in each samples were 0.5mg/mL.

Stability of RALA in Water (90℃)

Stability of RALA in heated water

RALA didn't dispersed in water. RALA was polymerized under heated condition.

Taste masking effect by γCD

Sensory test

Healthy adult aged 20's to 60's (Male 8, Female 7)

(Both RALA-γCD and RALA-MCC contain 11% of RALA)
*RALA-MCC:Physical mixture of RALA and crystalline cellulose.

Panelist didn't know the content of test sample.
Panelist rinses the mouth then lick the test sample followed by evaluation its pungency in the mouth.

No pungency = 0
1 (less pungency) to 10 (strong pungency)

【Screening and judge】
Two panelists who gave 1 score to γCD were eliminated.
Sum total of each sample were evaluated.


Pungent taste of RALA was decreased by γCD complexation.

Safety evaluation of RALA-γCD

Acute toxicity test



試験群:雄雌各5匹 検体投与量:2000mg/kg体重
対照群:雄雌各5匹 注射用水を投与


Body weight transition

mean ± S.D. (g)

Body weight (Male)

Group 0 day 7 days 14 days Dead (%)
Test 33.0±0.9 37.5±1.8 39.5±2.8 0 (0%)
Control 33.0±1.0 37.9±1.4 40.5±2.1 0 (0%)

Body weight (Female)

Group 0 day 7 days 14 days Dead (%)
Test 26.9±1.1 28.9±1.4 30.5±2.0 0 (0%)
Control 27.1±1.4 30.4±1.1 32.7±1.3 0 (0%)

LD50 > 2000mg/kgBW (Mice)



RALA can make inclusion complex by αCD, βCD and γCD.
The stability of RALA was improved by making inclusion complex with CD.
RALA-γCD complex was stable even in solution.
The pungency taste of RALA was decreased by γCD.
LD50 of RALA-γCD complex was > 2000mg/kgBW (mice).

RALA-γCD complex is now available as functional food materials !