## 4 Polyphenols
### Flavonoids
#### 4.1.3 Flavan-3-ols  
Like flavonols, flavan-3-ols of _U. tomentosa_ contain a hydroxy group at C-3 of ring C. However, unlike the previous subclasses, flavon-3-ols contain a C ring that is saturated and therefore possesses stereochemistry. The stereochemistry of C-2 that links the B and C ring is in the \(S\) configuration for all flavan-3-ols identified from _U. tomentosa_, while the stereochemistry of the hydroxy group can alternate (Figure 5, **35-37**). Procyanidins formed from monomers of flavan-3-ols have been isolated in _U. tomentosa_[2, 3, 86]. The monomers identified in _U. tomentosa_ are the compounds (\(-\))-epicatechin (**35**) and (\(+\))-catechin (**36**) (Figure 5). These compounds are stereoisomers. Several sources have indicated the presence of these monomers in _U. tomentosa_[2, 3, 82, 86, 87]. Procyanidin Type  
Proanthocyanidins are polymeric structures composed of flavan-3-ol monomer subunits (Figure 6). The most prevalent types of proanthocyanidin structures present in _U. tomentosa_ are procyanidins. Procyanidins are comprised of **35** and/or **36** flavan-3-ol monomers. These monomer units are described above and consist of a hydroxylated B ring, with the orientation of the C ring and hydroxy groups being in the _cis_ or _trans_ conformation. The prefix _epi_ is used to indicate a _cis_ configuration as indicated by (\(-\))-epicatechin (**35**). The number of monomers in a procyanidin structure can vary. Structures ranging from 2 to 10 monomers have been identified from polyphenolic assessment of _U. tomentosa_ utilizing mass spectrometry [88]. The molecular weight of procyanidin structures has been indicated to affect bioactivity when consumed, with lower molecular weights (degree of polymerization (DP) \(<\) 3) leading to absorption into the gastrointestinal tract and higher molecular weights (DP \(>\)3) possessing a lower bioavailability [86]. The monomers that comprise procyanidins can be joined via two different types of interflavan linkages, known as A- and B-type linkages. A-type linkages have two linkages: one between C-4 of the C ring and C-6 or C-8 of the B ring and an ether linkage from a hydroxy group on ring A to C-2 of ring C. B-type linkages occur between C-4 of the C ring and C-6 or C-8 of the A ring. The types of interflavan linkages present in procyanidins of _U. tomentosa_ include C-4\(\rightarrow\)C-6 B-type and C-4\(\rightarrow\)C-8 B-type linkages. The most common type of procyanidins found in nature consist of **35** with B-type linkages, which corresponds to those found in _U. tomentosa_[3, 87, 88, 89]. The procyanidin dimer structures present in extracts of _U. tomentosa_ have been identified extensively by [PERSON] and colleagues [2; 3; 86]. The dimer structures identified include procyanidin B1-B7 (Figure 6, **38-44**). These compounds can be more easily identified as reference material exists for these compounds unlike larger procyanidin structures. Some of the dimers have been indicated to possess antibacterial activity when isolated from other plant sources and tested for MIC. Evidence has been found to support the antibacterial activity of **38-40** when extracted from plants. Procyanidin **38** and **39** were isolated from _Antidesmu bunius_ L. and tested against a variety of bacteria. MIC values ranging from 0.12 to 125 \(\upmu\)g/mL were reported against Gram-positive bacteria and less potent MIC values ranging from 7.25 to 125 \(\upmu\)g/mL against Gram-negative bacteria [91]. This study also proposes that the mechanism of action can be attributed to an effect on the cellular membrane, referencing the stronger antibacterial effect on Gram-positive bacteria and previous investigations into the antimicrobial effect of other flavan-3-ols [92]. Additionally, **40** was isolated from _Quercus lex_ L. and demonstrated weak antibacterial activity ranging from 98.3 to 393.176 \(\upmu\)g/mL [93]. Three procyanidin trimers have also been identified by [PERSON] and colleagues. Two of the trimers were characterized using MS/MS alongside commercial standards.