Viniferin Forms Compared: A Structural Guide to Resveratrol Oligomers

The viniferins are resveratrol oligomers — dimers, trimers, and tetramers produced by oxidative coupling of the stilbene monomer. Five forms are commercially relevant as reference standards: epsilon-viniferin, delta-viniferin, alpha-viniferin, vitisin A, and vitisin B. The Greek-letter names are historically entrenched but structurally opaque. What actually distinguishes these compounds is the regiochemistry of their inter-resveratrol bonds, which determines scaffold type, biosynthetic relationships, and analytical behavior.

The coupling mode, not the Greek letter, is the useful sorting principle. ε-Viniferin and α-viniferin both arise from 8–10′ coupling; δ-viniferin, vitisin A, and vitisin B all involve 3–8′ coupling. Within each group, oligomer size and cyclization state further differentiate the members.

ε-Viniferin: the 8–10′ dimeric anchor

ε-Viniferin is the 8–10′ oxidative dimer of resveratrol, first isolated from Vitis vinifera by Langcake and Pryce in 1977 (Experientia, 33, 151–152). The 8–10′ connectivity generates a 2,3-diaryl-2,3-dihydrobenzofuran core with chiral centers at C-7a and C-8a. The trans configuration predominates in nature; the cis isomer is sometimes designated ω-viniferin in the literature.

Because the 8–10′ dihydrobenzofuran motif recurs throughout the higher oligomers, ε-viniferin functions as a biosynthetic hub. Trimers such as gnetin H and miyabenol C, and tetramers including vitisin A and vitisin B, are assembled by convergent coupling of ε-viniferin with resveratrol or with other dimers rather than by stepwise addition of monomers (Keylor, Matsuura & Stephenson, Chem. Rev., 2015, 115, 8976–9027).

δ-Viniferin: the 3–8′ regioisomer

δ-Viniferin (CAS 71126-73-5) shares the same molecular formula as ε-viniferin but differs in coupling regiochemistry. It is the 3–8′ oxidative dehydrodimer — the second major product of resveratrol phenoxyl radical coupling alongside the 8–10′ pathway. Both dimers carry the dihydrobenzofuran scaffold; the distinction lies in which carbons of the two resveratrol units are joined.

The 3–8′ dimer is biosynthetically significant because fungal laccases from Botrytis cinerea convert resveratrol to δ-viniferin efficiently. Pezet isolated a laccase-like stilbene oxidase from the pathogen that dimerized resveratrol to ε-viniferin in 97% yield, but other fungal oxidases favor the 3–8′ pathway, producing δ-viniferin and related 8–8′ dimers such as pallidol (Pezet, Phytopathology, 1998; Cichewicz et al., J. Nat. Prod., 2000).

α-Viniferin: the cyclotrimer

α-Viniferin (CAS 62218-13-7) is a resveratrol trimer — not a dimer — which makes it the clearest example of why Greek-letter nomenclature cannot be read as a size indicator. The structure is a cyclotrimer: three resveratrol units arranged in a ring closed by three 8–10′ dihydrobenzofuran linkages. The stereochemistry was confirmed by Kitanaka and co-workers in 1990 using heteronuclear correlation NMR (Chem. Pharm. Bull., 38, 2531–2534).

The cyclotrimer scaffold is assembled biosynthetically from ε-viniferin rather than from three independent resveratrol monomers. In biomimetic oxidation studies using horseradish peroxidase, (+)-ε-viniferin cyclizes to α-viniferin in 42% yield, establishing the direct biogenic relationship between the dimer and the trimer (Niwa et al., Chem. Lett., 1997, 26, ×××–×××; Keylor et al., Chem. Rev., 2015, 115, 8976–9027).

Vitisin A and vitisin B: tetramers

The tetrameric branch introduces a second naming system. Vitisin B is also known as R-viniferin (or r-viniferin); vitisin A is also known as R2-viniferin. Both names appear in the grapevine literature, and both should be indexed alongside the CAS number to avoid ambiguity.

Vitisin B / R-viniferin (CAS 142449-90-9) is the 3–8′ homocoupling product of two ε-viniferin radicals. It is the direct oxidative dimer of the dimer — a linear tetramer with two dihydrobenzofuran units joined through 3–8′ bonds. Niwa and co-workers isolated vitisin B in 6% yield from biomimetic peroxidase-mediated homocoupling of (+)-ε-viniferin (Tetrahedron, 2003, 59, ×××–×××; Keylor et al., Chem. Rev., 2015, 115, 8976–9027).

Vitisin A / R2-viniferin (CAS 142449-89-6) is a cyclized derivative of vitisin B. Acidic treatment of vitisin B in methanol effects a quantitative cyclization to vitisin A, converting the linear tetramer to a more constrained scaffold with an additional ring closure (Niwa et al., Tetrahedron, 2003, 59, ×××–×××; Keylor et al., Chem. Rev., 2015, 115, 8976–9027). The two tetramers share the same molecular formula but differ in ring connectivity.

The pyranoanthocyanin naming collision

"Vitisin A" and "vitisin B" also denote pyranoanthocyanin wine pigments — condensation products of grape anthocyanins with pyruvic acid (vitisin A) or acetaldehyde (vitisin B). These are flavonoid derivatives, not stilbenoids, and they bear no structural relationship to the resveratrol tetramers described above.

The collision is not a trivial indexing issue. An unconstrained search for "vitisin B" returns literature from both the stilbenoid and wine-pigment fields. The only reliable disambiguators are CAS number, compound class specification (stilbenoid tetramer vs. pyranoanthocyanin), and molecular formula cross-check. A procurement record that lists only the common name without CAS or class risks sourcing the wrong material.

Sourcing

Sylverity supplies ε-viniferin (CAS 62218-08-0), δ-viniferin (CAS 71126-73-5), α-viniferin (CAS 62218-13-7), vitisin A (CAS 142449-89-6), and vitisin B (CAS 142449-90-9) as Research Use Only (RUO) reference standards. Each lot ships with HPLC purity data and a Certificate of Analysis. Safety Data Sheet (SDS) is available on request.

Materials are for laboratory and analytical applications only. Not for human consumption, therapeutic use, or consumer resale.

For lot-specific documentation, quantity, or custom analytical requirements, contact the laboratory directly.