The investigation of post-thaw chilled storage and the applicability of large-scale cryopreservation in chub (Squalius cephalus) sperm

Chub (reophillic cyprinids) is one of the most sensitive bioindicator fish of environmental changes following anthropogenic activities. The improvement of different biotechnological procedures could help support its conservation and strengthen the natural populations. The aim of this study was to compare the effects of two different hormonal agents (carp pituitary extract and Ovopel™) on various motility parameters (pMOT-%, DAP-μm, VCL μm s-1, VSL-μm s-1, LIN-%, ALH-μm, BCF-Hz) of fresh and cryopreserved/thawed sperm (stored at 4 °C for 6 h). Additionally, we sought to develop a novel, large-scale cryopreservation method for chub sperm, assessing freezing methods (Styrofoam box and a controlled-rate freezer) and different containers (0.5, 5 mL straw and 4 mL cryotube) for sperm cryopreservation. The results of this study indicated no difference between the carp pituitary extract and Ovopel treated groups in either the fresh or frozen/thawed sperm (at 0, 3, 6, hour post thawing, P = 0.4351). In contrast, the quality of the thawed chub sperm was negatively affected after 3 h chilled storage in both hormonal treatments (P = 0.0036, P < 0.0001). When assessing the motility parameters of the sperm between the 5 mL straw and 4 mL cryotube groups cryopreserved in a Styrofoam Box, no difference was observed (P = 0.103). Additionally, sperm loaded in 4 mL cryotubes showed no difference in motility when cryopreserved with either the Styrofoam box or controlled-rate freezer methods (P = 0.109). A similar hatching rate was observed in sperm preserved using the Styrofoam box (35 ± 7 %) and controlled rate freezer (25 ± 9 %) methods (P = 0.300). In a second fertilization trial, hatching rate was similar between control (72 ± 19 %) and cryopreserved (4 mL cryotube and Styrofoam box, 61 ± 5 %) groups. (P = 0.257). Based on our findings and its standard features (less species specific, precise dose calculation), Ovopel can be a good candidate for the stimulation of spermiation in chub sperm prior to cryopreservation. Furthermore, our study presents a novel and applicable method for the large-scale cryopreservation of chub sperm.

The growth performance of pond-reared common carp (Cyprinus carpio) larvae propagated using cryopreserved sperm

The aim of our study was to determine the efficacy of utilizing cryopreserved common carp sperm (in comparison to fresh sperm) for propagation at a Hungarian aquaculture facility. The sperm was frozen in 5 mL straws using an extender method that was previously tested in common carp. Sperm motility was monitored using a computer-assisted sperm analysis system. The hatching and malformation rates among the specimens were recorded before the stocking of larvae in both groups. The growth (body weight, total length) and survival rates of the fish were measured during the pre-nursing (from May to June: between 1 and 26 days post hatching) and grow-out periods (from June to October: between 26 and 105 days post hatching) of the same year. The fresh sperm, which was collected and pooled prior to fertilization, showed high MOT (97%), pMOT (92%), VCL (106 µm s-1), LIN (75%), and ALH (1.84 µm). Prior to the fertilization trial of the cryopreserved sperm, low MOT (34%), pMOT (14%), and VCL (61 µm s-1) values were observed in frozen-thawed sperm. A significantly higher hatching rate was measured in the fresh sperm group (87%) when compared to the cryopreserved sperm group (42%). No significant difference in the overall malformation rate was observed in larvae originating from either the fresh or frozen sperm. A significant difference between the two test groups was observed in the incidence of deformed tails (fresh: 20%, cryopreserved: 55%). Except for one sampling period, no significant difference in the body weight and total length of the fish larvae was found between the two groups throughout the pre-nursing and grow-out periods. A significantly higher larvae survival rate was noted in the fresh sperm (72%) as compared to the cryopreserved group (43%) by the end of the pre-nursing stage. However, no significant difference in survival rate was observed for the cryopreserved sperm (96%) in comparison to the fresh sperm (95%) by the end of the grow-out stage. The results of this study showed, for the first time in large-scale pond culturing, an equal growth and viability in larvae propagated from cryopreserved sperm when compared to fresh sperm (despite the limited available rearing ponds provided by the commercial company).

Black Soldier Fly (Hermetia illucens) Meal as Direct Replacement of Complex Fish Feed for Rainbow Trout (Oncorhynchus mykiss) and African Catfish (Clarias gariepinus)

In the experiments, defatted black soldier fly meal reared on vegetable byproducts was used in the fry rearing of two economically important fish species, African catfish and rainbow trout. Both fish species were reared in a recirculation system and 0-33-66-100% of the complex fry feed was replaced by a defatted prepupae meal of black soldier flies during a 28-day feeding experiment. African catfish was reared at 25 ± 1 °C while rainbow trout was reared at 12 ± 1 °C. The results showed that the growth of African catfish was not significantly reduced when 66% of the feed was replaced by soldier fly meal (mean weight in the control fish group at the end of the experiment was 0.4632 ± 0.2469 g, while the 66% group resulted mean weights of 0.4150 ± 0.1886 g) and the survival did not show any statistically different results (mean survival in control group was 57.48 ± 13.76% while it was 56.6 ± 7.763% in the 66% group). In the case of rainbow trout, replacing the feed entirely with insect meal did not cause a decrease in weight gain (final mean weight in the control group was measured at 1.9640 ± 0.4154 g, while in the group consuming only insect meal, it was 1.9410 ± 0.4248 g) or in survival (in the control group 98.5%, while in the group consuming only insect meal 99.5%). All these preliminary results indicate that black soldier fly meal can be used directly as a nursery feed in fish farming as a partial or total replacement of complete feeds. The results showed that black soldier fly meal could replace 66% of the complex brood feed of African catfish and up to 100% of rainbow trout feed without deterioration of production results. Our experiments have therefore opened the way for further experiments on insect meal in larval rearing.

Repeated hormonal induction of spermiation affects the stress but not the immune response in pikeperch (Sander lucioperca)

Hormonal induction of spermiation, previously reported to be immunogenic in fishes, is a common hatchery practice in pikeperch, Sander lucioperca. The aim of the present study was to investigate the effects of repeated induction of spermiation in pikeperch, following application of either human chorionic gonadotropin (hCG) or salmon gonadoliberine analogue (sGnRHa) on sperm quality indices as well as on immune and stress response. Mature males of pikeperch (n = 7 per group) were stimulated twice with five days between injections of either hCG (hCG; 500 IU kg^-1), sGnRHa (sGnRHa; 50 μg kg^-1) or NaCl (control group; 1 ml kg^-1) to assess spermatozoa motility with a computer-assisted sperm analysis (CASA) system. During second sampling, blood plasma was sampled for humoral innate immune (peroxidase and lysozyme activities, ACH50), stress (cortisol, glucose) and endocrine (testosterone) markers. In addition, the head kidney was dissected to assay the expression of several immune genes (such as il1, c3, hamp, tnf-α and lys genes). The results indicate that hormonal treatment significantly increased sperm production. Sperm sampled after the hormonal treatment maintained its quality throughout the study, regardless of the sampling time. However, it appears that the application of hCG induced elevated cortisol and glucose plasma levels compared to the control group. Almost all immune markers, except the relative expression of hepcidin (hamp gene), were unaffected by the two hormones applied. The results showed that the induction treatment of spermiation processes in pikeperch resulted in an important physiological stress response for which the intensity varied according to the hormonal agent used. However, this stress response (more profound following application of hCG) was weakly associated with innate immune functions. On the other hand, a significant negative correlation between the expression of several important immune markers (peroxidase activity, relative expression of c3 and il1 genes) and sperm quality indices indicates significant involvement of immune status on sperm quality. The results obtained shed light on immune-system-induced modifications to sperm quality. The data presented here highlight the need for careful revision of broodstock management and selection practices where welfare status as well as individual predispositions of fish to cope with the stress should be taken under the consideration.

Development of sperm vitrification protocols for two endangered salmonid species: the Adriatic grayling, Thymallus thymallus, and the marble trout, Salmo marmoratus

Vitrification was applied to the sperm of two endangered fish species of Soča River basin in Slovenia, the Adriatic grayling (Thymallus thymallus) and marble trout (Salmo marmoratus) following testing different cooling devices and vitrifying media. Sperm was collected, diluted in species-specific non-activating media containing cryoprotectants, and vitrified by plunging directly into liquid nitrogen without pre-cooling. Progressive motility, curvilinear velocity, and straightness of fresh and vitrified-warmed sperm were evaluated with computer-assisted sperm analysis (CASA). Fertilization trials were carried out to test the effectiveness of vitrification in the case of grayling. A protocol utilizing a glucose-based extender, 30% cryoprotectants (15% methanol + 15% propylene glycol), 1:1 dilution ratio, and droplets of 2 μl on a Cryotop as cooling device yielded the highest post-thaw motility values for both Adriatic grayling (7.5 ± 6.5%) and marble trout (26.6 ± 15.8%). Viable embryos were produced by fertilizing eggs with vitrified grayling sperm (hatching 13.1 ± 11.7%, control hatching 73.9 ± 10.4%). The vitrification protocol developed in this study can be utilized in the conservation efforts for the two species as an alternative to slow-rate freezing when working in field conditions or when specific equipment necessary for slow-rate freezing is not available.

The comparison of two different extenders for the improvement of large-scale sperm cryopreservation in common carp (Cyprinus carpio)

In our study, a traditionally used (Grayling, already used in cyprinid species) and a newly tested (Pike) extender was tested to avoid sperm agglutination phenomenon following thawing during carp sperm cryopreservation. A large-scale (elevated volume of sperm) freezing method in a controlled-rate freezer using 5 ml straw and 10 ml cryotube was also systematically established. In all experiments, the sperm cryopreserved in using Grayling extender (except only one sample) showed an agglutination phenomenon (damaged and intact cells adhered to each other) after thawing where Pike extender resulted the regular cell suspension. No significant difference was observed between the two cryopreserved groups (Pike and Grayling extender) in all motility parameters using the 0.5 ml straw and the polystyrene box. Similarly, motility parameters did not show a significant difference in the two frozen groups with the 5 ml straw, also in the polystyrene box. A significantly higher progressive motility (pMOT, Grayling: 54% ± 8%, Pike: 37% ± 5%), straight line velocity (VSL, Grayling: 50 ± 5 µm/s, Pike: 39 ± 4 µm/s) and beat cross frequency (BCF, Grayling: 20 ± 1 Hz, Pike: 17 ± 1 Hz) was observed in the case of the grayling extender by the 5 ml straw cryopreserved in a controlled-rate freezer (CRF) compare to the pike extender. A significantly higher VSL (Grayling: 45 ± 3 µm/s, Pike: 38 ± 4 µm/s) was observed by the grayling extender using the 10 ml cryotube than with the pike extender. Despite the randomly occurring differences in a few parameters, our new controlled freezing method using the newly tested Pike extender, the 5 ml straw or the 10 ml cryotube can be a good solution for the preservation of elevated volume of carp sperm.

Effect of urine contamination on semen quality variables in Eurasian perch Perca fluviatilis L

The objectives of the present study were to determine values for semen quality variables in the Eurasian perch (i.e., osmolality of seminal plasma as well as sperm motility characteristics analyzed with CASA system) in response to (1) the method of milt collection (stripping or catheterization) and (2) experimental contamination of catheterized semen with urine (0%, 5%, 10%, 20%, 30% and 50% of contamination). Additionally, the effect of short-term chilled storage of experimentally contaminated semen (during the 24 h post semen collection period) on motility characteristics was investigated. Use of a typical stripping procedure resulted in about 5%-10% contamination of semen with urine, what is much less compared with other species. Markedly lesser values of straight line velocity (VSL) and consequently less linearity of spermatozoa movement (LIN) in perch semen, however, occurred as a result of stripping (46 ± 4 μm/s and 38 ± 4% for VSL and LIN, respectively), when compared to sperm collected by catheterization (87 ± 5 μm/s and 77 ± 2% for VSL and LIN, respectively), indicate that even a 10% contamination of semen with urine may have negative effects on quality. Exposure of semen to urine resulted in a significant dose-dependent decrease in the percentage of motile spermatozoa (MOT) and both velocity variables (VSL and VCL). Amount of urine contamination also affected MOT, VCL, VSL and LIN value during short-term storage. In conclusion, it is important to avoid semen contamination by urine when using the stripping procedure in the Eurasian perch, either for controlled reproduction or sperm preservation.

Development of sperm vitrification protocols for freshwater fish (Eurasian perch, Perca fluviatilis) and marine fish (European eel, Anguilla anguilla)

Vitrification was successfully applied to the sperm of two fish species, the freshwater Eurasian perch (Perca fluviatilis) and marine European eel (Anguilla anguilla). Sperm was collected, diluted in species-specific non-activating media and cryoprotectants and vitrified by plunging directly into liquid nitrogen without pre-cooling in its vapor. Progressive motility of fresh and vitrified-thawed sperm was evaluated with computer-assisted sperm analysis (CASA). Additional sperm quality parameters such as sperm head morphometry parameters (in case of European eel) and fertilizing capacity (in case of Eurasian perch) were carried out to test the effectiveness of vitrification. The vitrification method for Eurasian perch sperm resulting the highest post-thaw motility (14±1.6%) was as follows: 1:5 dilution ratio, Tanaka extender, 30% cryoprotectant (15% methanol+15% propylene-glycol), cooling device: Cryotop, 2μl droplets, and for European eel sperm: dilution ratio 1:1, with 40% cryoprotectant (20% MeOH and 20% PG), and 10% FBS, cooling device: Cryotop, with 2μl of sperm suspension. Viable embryos were produced by fertilization with vitrified Eurasian perch sperm (neurulation: 2.54±1.67%). According to the ASMA analysis, no significant decrease in head area and perimeter of vitrified European eel spermatozoa were found when compared to fresh spermatozoa.

Cryosurvival of isolated testicular cells and testicular tissue of tench Tinca tinca and goldfish Carassius auratus following slow-rate freezing

Experiments were carried out to test the efficiency of cryopreservation of whole testicular tissue in tench Tinca tinca and goldfish Carassius auratus and compare it to cryopreservation of isolated testicular cells. Additionally, effects of three cryoprotectants (dimethyl sulphoxyde - Me₂SO, methanol - MeOH and ethylene glycol - EG) at three concentrations (1M, 2M and 3M) on post-thaw cell viability were assessed. Tissue pieces/isolated testicular cells were diluted in cryomedia and cryopreserved by slow-rate freezing (1°C/min to -80°C followed by a plunge into the liquid nitrogen). In both species Me₂SO and EG generally yielded higher cryosurvival of early-stage germ cells than MeOH, while spermatozoa of neither species displayed such a pattern. In most cases a 3M>2M>1M viability pattern emerged in both species for both sample types regardless of the cryoprotectant used. Sample type (dissociated testicular cells vs testicular tissue) did not seem to affect viability rates of tench early-stage germ cells and goldfish spermatozoa, while the opposite was observed for tench spermatozoa and goldfish early-stage germ cells. Additionally, through histological analysis we displayed that tissue structure mainly remained unaltered after thawing in goldfish. These results indicate that cryopreservation of whole testicular tissue is indeed a valid alternative method to cryopreservation of dissociated testicular cells. Early-stage germ cells obtained from cryopreserved testis can be further used in different purposes such as transplantation into suitable donors while viable sperm might be used for fertilization when feasible.

Stimulus-triggered enhancement of chilling tolerance in zebrafish embryos

Background

Cryopreservation of zebrafish embryos is still an unsolved problem despite market demand and massive efforts to preserve genetic variation among numerous existing lines. Chilled storage of embryos might be a step towards developing successful cryopreservation, but no methods to date have worked.

Methods

In the present study, we applied a novel strategy to improve the chilling tolerance of zebrafish embryos by introducing a preconditioning hydrostatic pressure treatment to the embryos. In our experiments, 26-somites and Prim-5 stage zebrafish embryos were chilled at 0°C for 24 hours after preconditioning. Embryo survival rate, ability to reach maturation and fertilizing capacity were tested.

Results

Our results indicate that applied preconditioning technology made it possible for the chilled embryos to develop normally until maturity, and to produce healthy offspring as normal, thus passing on their genetic material successfully. Treated embryos had a significantly higher survival and better developmental rate, moreover the treated group had a higher ratio of normal morphology during continued development. While all controls from chilled embryos died by 30 day-post-fertilization, the treated group reached maturity (~90–120 days) and were able to reproduce, resulting in offspring in expected quantity and quality.

Conclusions

Based on our results, we conclude that the preconditioning technology represents a significant improvement in zebrafish embryo chilling tolerance, thus enabling a long-time survival. Furthermore, as embryonic development is arrested during chilled storage this technology also provides a solution to synchronize or delay the development.

Improvement of common carp (Cyprinus carpio) sperm cryopreservation using a programable freezer

The applicability of a programmable freezer for the increased-scale cryopreservation of common carp sperm was investigated. The effect of different equilibration times, cryopreservation methods, extenders, dilution ratios, activating solutions on the post-thaw motility of common carp sperm was investigated. The suitable post-thaw storage time-interval as well as fertilizing capacity of cryopreserved sperm was also examined. The motility, curvilinear velocity (VCL) and straightness (STR) values did not decrease significantly during 60min of equilibration neither in equilibrated nor thawed groups. Motility parameters of thawed sperm were similar using a conventional cryopreservation technique using a polystyrene box [motility (33%), VCL (47μm/s) and STR (88%)] and a programmable freezer: [motility (32%), VCL (54μm/s) and STR (89%)]. The highest motility and VCL was measured with a sugar based extender (grayling extender) at a ratio 1:9 (motility: 52%, VCL: 76μm/s) and 1:20 (motility: 49%, VCL: 76μm/s). The activating solution for cyprinids (ASC) could prolong sperm movement up for 2min. A storage time of six hours following thawing did not have a significant effect on the motility parameters of thawed carp sperm. Agglutination was observed during cryopreservation of an elevated volume of sperm whereas motility 47%, VCL 62μm/s and STR 91% were measured after thawing. Fertilization rate with thawed sperm (32%) was significantly lower compared to the control group (73%). According to our results, the developed method using a programmable freezer is suitable for the cryopreservation of elevated number of straws. However, carp sperm agglutination during freezing may have a negative effect on the fertilizing capacity.

Basic forms of supramolecular self-assembly organized by parallel and antiparallel hydrogen bonds in the racemic crystal structures of six disubstituted and trisubstituted cyclopentane derivatives

A selection of stereoisomeric 2-hydroxy-1-cyclopentanecarboxamides, a 4-tert-butyl derivative and three tert-butyl derivatives of the respective carboxylic acid were subjected to X-ray crystallography. The optically active molecules (I)--(VI) form racemic crystals. Each racemic structure is basically determined by two intermolecular hydrogen bonds of O--H...O==C--XH and O==C--X--H...OH types (X = O, NH). The partially similar patterns of close packing observed reflect five basic forms of supramolecular self-assembly. In the racemic crystals of chiral molecules, there are homo- and heterochiral chains of molecules formed by the principal (O--H...O==C) hydrogen bonds. These chains assemble either in a parallel or antiparallel mode. The parallel homochiral chains (hop) observed in structure (II), (1R*,2R*)-2-hydroxy-1-cyclopentanecarboxamide, demand the polar space group Pca2(1), while the parallel heterochiral chains (hep) are organized in antiparallel layers with space group P2(1)/n in structure (VI), (1R*,2S*,5R*-5-tert-butyl-2-hydroxy-1-cyclopentanecarboxylic acid). Heterochiral chains in an antiparallel array (hea) are found in (I), (1R*,2S*)-2-hydroxy-1-cyclopentanecarboxamide, and (V) [(1R*,2S*4S*)-4-tert-butyl-2-hydroxy-1-cyclopentanecarboxylic acid, space group P2(1)/c]. Structures (IV), (1R*,2S*,4R*)-4-tert-butyl-2-hydroxy-1-cyclopentanecarboxylic acid, and (III), (1R*,2R*,4S*)-4-tert-butyl-2-hydroxy-1-cyclopentanecarboxamide, reveal that homochiral chains in an antiparallel array (hoa; cross-linked by heterochiral dimers held together by the second hydrogen bonds) can be formed by either translation (space group P1) or a screw axis (space group P2(1)/c). These alternatives are denoted hoa1 and hoa2. Similarly, within each pattern (hea, hep and hop) two slightly different alternatives can be expected. The partial similarities in the identified five patterns of hydrogen bonding are described by graph-set notations. Structures (I), (IV) and (V) can be characterized by a common supramolecular synthon, while the highest degree of similarity is shown by the isostructurality of (I) and (V).

[Preparation and steric structure elucidation of saturated or partially saturated isoindolo[2,1-a][3,1]benzoxazinones, -[1,2-b][2,4]benzoxazepinones, cyclopentane- and -cyclohexane[b]pyrrolo[2,1-a][3,1]-benzoxazines]

The reactions of 2-carboxybenzaldehyde (1) with 1,3- or 1,4-aminoalcohols (2a-i, 3a,b) were used to prepare partially or fully saturated tetra- and pentacyclic compounds containing a condensed 1,3-oxazino- or oxazepinoisoindolone moiety and one terminal saturated carbocycle. Isoindolo[2,1-a][3,1]benzoxazinones (4a-d, 6, 7), stereoisomeric isoindolo[1,2-b][2,4]benzoxazepinones (5a-c) hexahydrocyclopentane[b]pyrrolo[1,2-a][3,1]-benzoxazinone (10a,b), octahydroindolo[1,2-b]- and decahydroindolo[1,2-a]benzoxazinone (11a,b and 12a,b) and related pentacyclic derivatives (4e-g) were prepared. The diastereomers 5a-c differ in the ring annelation or in the position of the NCHO hydrogens and annelational hydrogens. The stereostructures of these compounds were elucidated by means of 1H and 13C NMR spectroscopy, including DNOE, DEPT, 2D-HSC measurements and X-ray analysis.

[Saturated heterocyclic compounds. 216 (1). Synthesis, structure and ring opening of trans-perhydro-1,4-benzoxazepin-3-one derivatives]

trans-Perhydro-1,4-benzoxazepin-3-ones 2a-e were synthesized and transformed to condensed-skeleton perhydro-trans-1,4-benzoxazepines 3a,b, the thiones 4a,b, the urea derivatives 5a,b, and N-acylated compounds 6a-e. Compounds 6b,d were ring-opened by hydrochloride acid in ethanol to yield trans-2 (1-carbethoxyethoxy)-1-(acylaminomethyl)-cyclohexane derivatives 7b,d. The 1H- and 13C-nmr investigation and X-ray analysis of 5b and 6c,d proved that the expected N-acylated derivatives were formed and that both rings of the annolated compounds have a chair conformation.

[Preparation and steric structure of condensed-skeleton saturated diphenyl-substituted isoindolones]

The Friedel-Crafts reaction of benzene with cis-4-cyclohexene-1,2-dicarboxylic anhydride (1) yields trans-5-phenyl-cis-2-benzoylcyclohexanecarboxylic acid (2), which gave cyclohexane-condensed pyridazinone (3) with hydrazine, and cis-4,5-tetramethylene-1,2-oxazin-8-one (4) with hydroxylamine. From 2 with ethylenediamine, the saturated imidazol[2,3-a]iso-indolone (5) was prepared, while the reaction of 2 with 1,3-diaminopropane furnished a mixture of two isomeric pyrimido[2,3-a]isoindolones (6a,b) in the relative positions of the benzene ring and cyclohexane annelation hydrogens. From the reaction of 2 with 3-aminopropanol, the oxazino[2,3-a]isoindolone (7) was obtained. The reaction of 2 with cis-2-hydroxymethylcyclohexylamine gave the tetracyclic (8), while 2 and diendo-3-hydroxymethylbicyclo[2.2.1]hept-5-enyl-2-amine yielded the isomers (9a,b), which differ in the mutual positions of the phenyl group on the quaternary carbon and cyclohexane annelation hydrogens. 1H and 13C-nmr spectra and DNOE and 2D-HSC measurements proved that the 5-phenyl group is cis-equatorial to the two annelated hydrogens of the cyclohexane ring.

[Synthesis of quinazolino-1,3-benzothiazine derivatives]

The ring-closure reactions of N-(3,4-dimethoxyphenylthio-methyl)-2-nitrobenzamide derivatives 5a,b with phosphoryl chloride gave 4-(2'-nitrophenyl)-2H-1,3-benzothiazine derivatives 7a,b, which on reduction yielded 4-(2'-aminophenyl)-3,4-dihydro-2H-1,3-benzothiazines 8a,b. Reaction of these compounds with phosgene led to the derivatives 9a,b of a new heterocyclic ring system, 6H,8H-quinazolino[3,4-c] [1,3]benzothiazine. The structures of the title compounds were proved by their ir and nmr (1H, 13C) spectra.

[Synthesis of tert-butylcyclopentane-fused 1,3-oxazines and 1,3-thiazines]

Chlorosulphonyl isocyanate (CSI) addition to 4-tert-butylcyclopentene furnished the azetidinone (3) in a stereospecific reaction. Azetidinone 3 was transformed by ring opening esterification and lithium aluminium hydride (LAH) reduction to the 2-hydroxy-methyl-4-tert-butyl-1-cyclopentylamine (6). The N-methyl-aminoalcohol (8) was prepared from amino esters (5) with ethyl chloroformate and subsequent LAH reduction. By different ring-closure methods, a number of tert-butyl-cyclopentante-fused 1,3-oxazines and 1,3-thiazines were synthesized. A comparative study of the prepared compounds was performed by IR, 1H- and 13C-NMR, DEPT and DNOE measurements.

Effects of N-substitution on the fragmentations of some cyclohexene-fused 2-N-phenyliminoperhydro-3,1-oxazines and related thiazines

Six cyclohexene-fused 2-N-phenyliminoperhydro-3,1-oxazines and four related thiazines were prepared and their mass spectrometric behavior was studied by means of metastable ion analysis and exact mass measurement. In most of the fragmentations, extensive rearrangements took place. The decompositions through the retro-Diels-Alder reaction initiated by the double bond dominated in the case of the unsubstituted compounds. The effect of the double bond, however, was greatly outweighed by the effect of the substituent on the ring nitrogen atom. In comparison with the unsubstituted compounds, both electron-releasing (methyl) and electron-withdrawing (benzyl) substituents increased the contribution of the ring cleavage reactions in the heterocyclic part of the molecule; in the case of the benzyl group the loss of the substituent also became important. For isomeric compounds, the relative peak intensities were so different that such compounds were easy to differentiate.