In this second part of the investigation of volatiles and semivolatiles in Boswellia gum resins, an additional five less common species were analyzed by (SPME-)GC/MS, namely B. ameero, B. elongata, B. neglecta, B. popoviana, and B. rivae. Moreover, the results of hybridization experiments are reported in combination with the volatile composition of their gum resins. Our study shows that B. sacra benefits from an intraspecific cross-pollination, as the resulting hybrid B. sacra var. supersacra has a far higher seed germination rate and viability.

The genus Boswellia comprises many species which are famous for their production of frankincense, a fragrant gum resin. In the published literature, manifold studies on the volatiles and semivolatiles in individual samples of these gum resins exist, yet very few studies have investigated multiple samples. Contradictory results with regard to the volatile composition exist in literature. In this first part of the study, a large sample set (n = 46) of mostly commercially obtained gum resins and essential oils was investigated by solid-phase microextraction gas chromatography/mass spectrometry. A total of 216 compounds were identified or tentatively identified from the four commercially relevant species, namely B. sacra, B. serrata, B. papyrifera, and B. frereana, and the statistical evaluation of the resulting chemical profiles allowed a clear distinction between the species by their volatile profile. With only few exceptions, the designated species was found to be in accordance with the composition reported in reliable literature sources and detected in botanically identified samples. Chemotaxonomic marker substances were suggested to facilitate the differentiation of commercial gum resins or essential oils based on their volatile profile.

The present study aimed at analyzing the odor properties of a group of physiological human metabolites of the odorant 1,8-cineole: 2,3-dehydro-, α2,3-epoxy-, α/β2-hydroxy-, α3-hydroxy-, 4-hydroxy-, 7-hydroxy-, 9-hydroxy-, 2-oxo-, and 3-oxo-1,8-cineole. These metabolites constitute a group of structurally closely related molecules, which differ mainly in nature and position of O-containing functional groups. They thus offer the possibility to correlate odor properties with molecular structure, i.e., to establish structureodor relationships of compounds that are biologically generated from a potent odorant as parent substance. Generally, the metabolites preserved the eucalyptus-like odor quality of 1,8-cineole but showed additional odor notes such as sweet, citrus-like, plastic-like, earthy, musty, and faecal, which made them distinguishable. The individual enantiomers of chiral molecules also exhibited different odors. With the exception of 2,3-dehydro-1,8-cineole, all metabolites showed a highly decreased odor threshold in comparison to 1,8-cineole. The determination of odor qualities and odor thresholds was accomplished by gas chromatography/olfactometry (GC/O) on achiral and chiral GC capillaries. The results were correlated with common theories on structureodor relationships.

Human sperm chemotaxis to follicular fluid has been well established, but the molecular mechanism(s) for this phenomenon are still largely unclear. Studies indicate that odorant receptors expressed on spermatozoa could play a role in this scenario. It has recently been shown that several synthetic floral scents activate the receptors OR1D2, OR4D1, and OR7A5 in vitro and evoke distinct sperm motility patterns in vivo. However, all agonists found so far are of synthetic origin and, thus, the presence of endogenous structural analogues in female bodily fluids is subject to speculation. Therefore, the aim of the study reported herein was to investigate the occurrence of odor compounds in vaginal secretions and follicular fluid by using gas chromatography–olfactometry. Chemically identified constituents of either bodily fluid were then analyzed for activation of recombinant chemoreceptors and candidate ligands were further tested for induction of sperm Ca²⁺ signals. Through using this approach, two novel odorant receptor–ligand pairs are reported and human sperm Ca²⁺ elevations in response to both odorous substances, namely 5α-androst-16-en-3-one and 4-hydroxy-2,5-dimethyl-3(2H)-furanone, are shown.