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Chemistry

Herb Walk

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Herb Walk participants (Stephen, Thomas, Fiona, Helen, Rose) and our guide, Max Drake from The Urban Fringe Dispensary

Herb Walk participants (Stephen, Thomas, Fiona, Helen, Rose) and our guide, Max Drake from The Urban Fringe Dispensary

A couple of weeks ago, Picture It… Chemistry invited a local herbalist (Max Drake from The Urban Fringe Dispensary) to guide fellow plant and chemistry enthusiasts on an evening herb walk in the local Brandon Hill Park in Bristol.

Many of our posts so far have explored the culinary and medicinal uses of the compounds found in plants, and in this post Natalie has again taken her camera along to “the outside” to find out more about the plants and herbs that can be found in a local park, just a small distance from the School of Chemistry. As for previous “expeditions”, this post will mainly show pictures and a few links to get you interested, while we plan to explore some of these plants and molecules in detail in later posts. We looked at around 30 different plants, so the ones mentioned here are just a few examples.

Verbascum (sadly not yet showing its yellow flowers)

Verbascum (sadly not yet showing its yellow flowers)

Our little group consisted of fellow chemists Rose, Stephen and Thomas, as well as Fiona (a friend of Rose), Helen (a student of herbal medicine), our guide Max, and yours truly, camera in hand. Our first stop was at the flower bed at the entrance to Cantock’s Close, where Max showed us some wild opium lettuce, as well as Verbena bonariensis, a cultivated relative of blue vervain, a garden cultivar of Achillea (more about that later), and the Verbascum shown in the picture on the left. While the plant we saw is again likely to be a garden-worthy cultivar, the leaves and roots of the related Verbascum thapsus plant, commonly known as mullein, have been used to treat coughs and ear infections in herbal medicine. This has led to further chemical analysis of the compounds that can be extracted from this plant, such as verbacoside, described in J. Nat. Prod., 1989, 52, 640–643. Mullein has been linked to antimicrobial, antitumor, antiviral, antifungal and antibacterial activity, and it has been suggested that a number of plants have evolved to produce such compounds because they do not have an immune system to protect them from soil bacteria, so have to resort to chemical defences (discussed in Evid. Based Complement. Alternat. Med. 2011; 2011: 239237).

The flower bed on the entrance to Cantock's Close, showing one of the two sandstone nodules in the background.

The flower bed on the entrance to Cantock’s Close, showing one of the two sandstone nodules in the background.

The flower bed also contains two huge sandstone nodules (the smaller one weighs five tons). These were found in 1837 during the excavation of the Great Western Railway Tunnel near St Anne’s, Bristol, by Isambard Kingdom Brunel’s workmen. These nodules date from the Late Carboniferous period over 300 million years ago, and they clearly fascinated Brunel. They arrived in Cantock’s Close in 2009.

View from Brandon Hill Park (Bristol).

View from Brandon Hill Park (Bristol).

We then continued on to Brandon Hill Park, a short distance from the University buildings and a good vantage point for views across the City of Bristol. On our way into the park, Max alerted us to a number of what most gardeners consider to be weeds: dandelion (Tharaxacum officinale), herb robert (Geranium robertianum) and plantains, both broadleaf (Plantago major) and narrowleaf or ribwort (Plantago lanceolata).

Broadleaf plantain (Plantago major)

Broadleaf plantain (Plantago major)

The plantains have been used to stop bleeding, heal cuts and wounds and alleviate bites and stings in herbal medicine, and Max described how he once accidentally confirmed this when he cut himself while cutting up plantain leaves and the cut bled very little. The chemical basis of these observations has been reviewed recently (Journal of Ethnopharmacology 2001, 71, 1–21), suggesting that plantains contain a number of interesting compounds. Interestingly, in North America the broadleaf plantain is sometimes called White Man’s Footprint, because it grows particularly well where grass has been trampled, for example at the entrance to cattle fields.

Narrowleaf plantain, also called ribwort (Plantago lanceaolate)

Narrowleaf plantain, also called ribwort (Plantago lanceolata).

Tansy (Tanacetum vulgare)

Tansy (Tanacetum vulgare)

We continued, discussing elderflowers on our way to a bed full of herbs below Cabot Tower, where we spent a while looking at the different plants there: feverfew, borage, lemon balm, comfrey, c(h)amomile, sage, mint, lavender, fennel, angelica, nigella, rosemary, thyme, nepeta, as well as tansy. This last one, Tanacetum vulgare, has found use as an insect repellent and insecticide, as well as a wormifuge in herbal medicine. Tansy oil is volatile and toxic and contains a number of compounds including thujone, which can also be found in absinthe. We also discussed that natural fluctuations in growing conditions mean that tinctures and plant extracts cannot be standardised very easily, which, as Max agreed, can make it more difficult to understand and administer some herbal remedies.

On leaving the bed of herbs, we walked past a cultivar of Hypericum, which is know in herbal medicine as St. John’s Wort (Hypericum perforatum) and often prescribed for the treatment of depression in alternative medicine.

Hypericum cultivar, relative of Hypericum perforatum, St John's Wort.

Hypericum cultivar, relative of Hypericum perforatum, St John’s Wort.

Max and I had discussed how our chemical understanding of plant remedies often lags behind their successful application, further complicated if the extraction or synthesis of individual components is challenging. In addition, some compounds do not show activity in isolation, while the natural blend of compounds appears to be effective. This has been postulated to be the case for St. John’s Wort, as summarised on Wikipedia. Two of the key compounds extracted from this plant are hyperforin and hypericin. Enantioselective synthesis of hyperforin has recently been achieved in 18 steps (J. Am. Chem. Soc., 2013, 135, 644–647), which might help with its study. Some of the potential uses of hypericin have been discussed in the following paper: Current Pharmaceutical Design, 2005, 11, 233-253.

Max Drake, holding a bit of yarrow (Achillea millefolia) to illustrate how this looks like a circulatory system.

Max Drake, holding a bit of yarrow (Achillea millefolium) to illustrate how this looks like a circulatory system.

In a patch of grass, Max spied some yarrow, Achillea millefolium, one of the few examples where the outward appearance and structure of a plant relates to its uses (sympathetic magic): the yarrow looks like a network of veins and arteries and has indeed been used to benefit the circulatory system. The isolation of achilleine was described in 1954 (J. Am. Chem. Soc., 1954, 76, 1353–1354) and describes faster blood clotting, but more recent work suggests that multiple other compounds can also be found in extracts from this plant (Food Chemistry 2013, 141, 4152–4160).

We agreed to go on for a little longer than our allotted hour and took in some lime trees, where the flowers are used to make limeflower tea, thought to be calming, as well as astringent geranium flowers and ox-eye daisies. In an area where the grass was left to grow, Max also found some red clover and told us about its uses for perimenopausal symptoms as well as breast cancer.

Red clover (Trifolium pratense).

Red clover (Trifolium pratense).

Red clover (Trifolium pratense) produces compounds that have estrogen-like effects (phytoestrogens), which can potentially interfere with other treatments described by conventional medicine and accelerate the growth of cancers responding to hormones. On the other hand, these effects may be beneficial in some cases, making the use of red clover controversial, as discussed on this page from the University of Maryland Medical Centre. An article in the Clinical Medicine, the journal of the Royal College of Physicians, provides an overview of the review of different herbal medicines (Clin. Med. 2013, 13, 7-12), which references a full review of red clover published in 2002 (Journal of Herbal Pharmacotherapy 2002, 2, 49-72).

We concluded our walk with a discussion of the uses and properties of hawthorn and then headed home with a better understanding of the plants around us. Many thanks to Max Drake for providing us with expert guidance, and to Rose, Fiona, Stephen, Thomas and Helen for coming along!

Contributors: Natalie Fey (photography and words), Rose Silvester (information about Brunel’s sandstone nodules).

 

 

 

 

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