What molecule am I?
Aloin (aka aloin A, barbaloin) is a natural compound found in the exudate of dozens of species of Aloe, flowering succulent plants that grow or are cultivated worldwide. Aloin A has a diastereomer, aloin B1 (aka isobarbaloin), that has similar properties.
Aloin, as barbaloin, was described in 1905 by Hooper Albert Dickinson Jowett* and Charles Etty Potter at Wellcome Chemical Works (Dartford, UK). The authors stated that the compound was first isolated in 1850 and examined during the late 1800s by several researchers. Jowett and Potter reported an empirical formula for barbaloin of C10H18O7, which turned out to be wildly incorrect.
In 1907, French chemist E. Léger reported that barbaloin transforms at 160–165 ºC to a product that he called “β-barbaloin”. It now appears that barbaloin epimerized to isobarbaloin, and what Leger made was a mixture of the two diastereomers2. In the following years, Léger went on to publish more research on the aloins, particularly β-barbaloin.
The aloe species Aloe vera has a long history of use as an herbal medicine, beginning in ancient Greece and Rome. Uses included wound treatment and laxatives. In modern times, a variety of personal care products and over-the-counter (OTC) medications contain extracts of aloe plants. In 2002, however, the US Food and Drug Administration banned the use of aloe-containing products in OTC laxatives because aloin and its derivatives were suspected carcinogens.
Despite that setback, research on the medical value of aloins continues. Last July, Danilo Milardi at the National Research Council of Italy (Catania facility) and collaborators there and at the Universities of Catania and Naples wrote extensively about the therapeutic potential of aloins A and B. They reported these findings:
- “The structural differences between these two epimers suggest that they may exhibit distinct pharmacological properties.”
- “. . . both epimers are not stable in aqueous solution . . . underscor[ing] the importance of addressing issues such as the need for encapsulation into effective drug-delivery systems to enhance stability.”
- “. . . an equimolar mixture of aloin A and aloin B demonstrated an ability to inhibit proteasome in-tube tests, which is suggestive of potential anticancer properties . . .”
- “Higher water stability and increased antiproliferative activity were observed by encapsulation in carbon dot nanoparticles, suggesting a promising potential for further in vivo studies.”
1. CAS Reg. No. 28371-16-6.
2. CAS Reg. No. 452311-56-7.
Aloin hazard information*
| Hazard class** | GHS code and hazard statement | |
|---|---|---|
| Acute toxicity, oral, category 4 | H302—Harmful if swallowed |  |
| Skin corrosion/irritation. category 2 | H315—Causes skin irritation | |
| Serious eye damage, category 2A | H319—Causes serious eye irritation | |
| Specific target organ toxicity, single exposure, respiratory tract irritation, category 3 | H335—May cause respiratory irritation | |
*Compilation of multiple safety data sheets.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.
Winter Remedy Molecules
What’s better than honey to soothe a sore throat? Several former Molecules of the Week are found in various sources of honey, including flavonoids chrysin1, kaempferol2, and quercetin3; and phenolic acids chlorogenic acid4, p-coumaric acid5, and gallic acid6.
But wait—there’s much more. A 2018 review written by Francesca Giampieri and Maurizio Battino at Marche Polytechnic University (Ancona Italy) and coauthors there and at three Spanish universities lists 27 flavonoids and phenolic acids contained in sources of honeys ranging from acacia trees and shrubs (Acacia spp.) to clover (Trifolium spp.) to thyme (Thymus spp.) and their associated health benefits. In addition to the molecules mentioned above, prominent components of some honeys are the flavonoids pinocembrin7 and pinobanksin8 and the phenolic acid syringic acid9.
Pinocembrin and pinobanksin are antioxidants and major components of honey from sunflowers (Helianthus spp.), as identified in 1992 by M. J. Amiot at the National Institute of Agronomic Research (Avignon) and coauthors there and at the Technical Institute of Apiculture (Bures-sur-Yvette, both in France). Pinobanksin is a biosynthetic product of pinocembrin.
Syringic acid, along with pinocembrin, contributes to the antimicrobial properties of honeys, as described in 2006 by Esther O. Agbaje*, T. Ogunsanya, and O.I.R. Aiwerioba at the University of Lagos (Nigeria). The honeys that the researchers studied were effective against some pathogenic bacteria, especially Staphylococcus epidermidis (originally S. albus); the results were similar to those from conventional antibiotics such as ciprofloxacin and tetracycline.
1. CAS Reg. No. 480-40-0.
2. CAS Reg. No. 520-18-3.
3. CAS Reg. No. 117-39-5.
4. CAS Reg. No. 327-97-9.
5. CAS Reg. No. 501-98-4.
6. CAS Reg. No. 149-91-7.
7. CAS Reg. No. 149-91-7.
8. CAS Reg. No. 149-91-7.
9. CAS Reg. No. 149-91-7.
Winter Remedy Molecules
Throughout January, MOTW is featuring key components of natural substances that people use when they have coughs or runny noses.—Ed. See this week's winter remedy.
This molecule was suggested by a reader. We present almost all of the molecules suggested by our readers. If you have a molecule you would like us to consider, please send us a message. And thank you for your interest in Molecule of the Week! —Ed.
Aloin fast facts
| CAS Reg. No. | 1415-73-2 |
| SciFindern name | 9(10H)- Anthracenone, 10-β-D- glucopyranosyl- 1,8-dihydroxy-3- (hydroxymethyl)-, (10S)- |
| Empirical formula | C21H22O9 |
| Molar mass | 418.39 g/mol |
| Appearance | Yellow crystals or powder |
| Melting point | 148–149 ºC |
| Water solubility | 83 g/L (25 ºC) |
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