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The structure of gamma-oryzanol is:

γ-Oryzanol structure

What does the "gamma" in its name mean?

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No designations such as alpha-oryzanol, beta-oryzanol, etc. appear to be in use, and according to this WebMD entry, as well as this PubChem document, another name for gamma-oryzanol is simply "oryzanol".

There seems to be some ambiguity as to just what oryzanol, or gamma-oryzanol refers to. According to Chemical Book:

Gamma Oryzanol is a mixture of 6 substances derived from rice bran oil, including sterols and ferulic acid, called Cycloartanyl Ferulate or Triterpene alcohol ferulate.

But then other sources, including this US National Institutes of Health publication, consider gamma-oryzanol composed of four components:

There are four main components of γ-oryzanols, namely, cycloartenyl ferulate, 24-methylene cycloartenyl ferulate, campesteryl ferulate, and sitosteryl ferulate [original publication: Lerma-García M. J., Herrero-Martínez J. M., Simó-Alfonso E. F., Mendonça C. R. B., Ramis-Ramos G. Composition, industrial processing and applications of rice bran γ-oryzanol. Food Chemistry. 2009;115(2):389–404. doi: 10.1016/j.foodchem.2009.01.063

Further confusing the issue is that the PubChem article referenced above gives a single structure for gamma oryzanol (the same as that given in the OP), but does not include any physical properties that one would expect for a single pure compound (i.e. no melting point, solubility, vapor pressure data) although it does give the molecular weight. Again, PubChem lists "oryzanol" as a synonym and does not have any other oryzanol-named compound in it's database.

Summary TL/DR:
The gamma in "gamma-oryzanol" doesn't refer to a specific structure or isomer and there is no corresponding compounds named alpha-oryzanol, beta-oryzanol, etc. Rather, the term gamma-oryzanol is also simply called "oryzanol" and it refers to a combination of several different moieties as described above.

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  • $\begingroup$ Is it possible that this name is related to the type or location of the ring? $\endgroup$ – M. A Ghajari Apr 20 '17 at 15:29
  • $\begingroup$ That's sure the first thing you'd think, but I don't see where there's a significant functional group "gamma" to another. Also, you'd expect the term in that context to differentiate from another conformation like an alpha or beta position and there is just nothing in any chemical database I can find referring to anything but "gamma" or simply oryzanol. Maybe there is some historical significance to the naming, but I'm not sure what that would be. As far as modern nomenclature, I think of PubChem as being a pretty authoritative source. $\endgroup$ – airhuff Apr 20 '17 at 15:43
  • $\begingroup$ No problem. If you found the answer useful, the way we say thanks here is by accepting the answer (with the check box next to the answer). Cheers... $\endgroup$ – airhuff Apr 21 '17 at 5:49
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Some works directly mention the alpha and beta designated substances – that were (incl. gamma) rather fractions obtained during first historic isolations:[1]

(…) Oryzanol occurs in the unsaponifiable fraction of rice bran oil and is so named because it was first discovered in rice bran oil (Orysae Sativa L.) (Kaneko and Tsuchiya, 1954)[2] and contained a hydroxyl group. Oryzanol was originally considered a single compound but later was determined to be a mixture of ferulic acids esterified with normal sterols or triterpene alcohols, called α-, β- and γ-oryzanol, of which γ-oryzanol has been the most commonly mentioned. The sterol components of γ-oryzanol are primarily campesterol and sitosterol, and the triterpene alcohol components are cycloartenol and 24-methylene cycloartanol (…)

Other text sound like alpha a beta fractions were not oryzanol at all:[3]

(…) During their studies, a number of lipid fractions were isolated from rice bran oil; the third (gamma) fraction isolated was oryzanol[2]. Its chemical composition was later identified as a mixture of ferulic acid esters of various plant sterols (…)

(Hard to tell, the article[2] is in Japanese.)

As airhuff already said in his answer, γ-oryzanol (or just oryzanol) is a mixture of various sterol ferulates, which now usually are listed by their chemical names, however a couple of notable compendia[4,5] list the two major[6] formerly isolated constituents under names oryzanol A and C (no B, since it turned out to be a mixture of A and C[7]).

Fig. - structures

  • (I) oryzanol A, CAS 21238-33-5, cycloartenyl ferulate,
    9,19-cyclo-5α-lanost-24-en-3β-yl (2E)-3-(4-hydroxy-3-methoxyphenyl)prop-2-enoate

  • (II) oryzanol C, CAS 469-36-3, 24-methylenecycloartanyl ferulate,
    24-methylidene-9,19-cyclo-5α-lanostan-3β-yl (2E)-3-(4-hydroxy-3-methoxyphenyl)prop-2-enoate

Your structure happens to be oryzanol A.


References:

  1. Huang, C. J. Potential Functionality and Digestibility of Oryzanol as Determined Using in Vitro Cell Culture Models, Dissertation thesis, Louisiana State University and Agricultural and Mechanical College, 2003.
  2. Kaneko, R.; Tsuchiya, T. New Compound in Rice Bran and Germ Oils. J. Chem. Soc. Jpn. 1954, 57, 526–529.
  3. Wheeler, K. B.; Garleb, K. A. Gamma Oryzanol—Plant Sterol Supplementation: Metabolic, Endocrine, and Physiologic Effects. International Journal of Sport Nutrition 1991, 1 (2), 170–177.
  4. O’Neil, M. J.; Heckelman, P.; Koch, C.; Roman, K. The Merck Index, 14th ed.; 2006.
  5. Hill, R. A.; Makin, H.; Kirk, D.; Murphy, G. Dictionary of Steroids; CRC Press, 1991.
  6. Xu, Z.; Godber, J. S. Purification and Identification of Components of γ-Oryzanol in Rice Bran Oil. J. Agric. Food Chem. 1999, 47 (7), 2724–2728.
  7. Shimizu, M.; Ohta, G. Studies on the Constituents of Rice Bran Oil. V. Reexamination of Oryzanol-B. Chem. Pharm. Bull. 1960, 8 (2), 108–111.
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