Synthesis of meta-Carboranyl-(S)-homocysteine Sulfoxide

Synthesis of Charge-Compensated nido-Carboranyl Derivatives of Sulfur-Containing Amino Acids and Biotin

“…For the selective functionalization of nido-carborane at position B(9), we used an approach based on the demethylation of 9-dimethylsulfonio-nido-carborane (12), by analogy with known methods, 27d,e,28a followed by alkylation. Treatment of compound 12 with sodium in the presence of naphthalene followed by the action of cesium fluoride led to the cesium salt 9-methylthio-nido-carborane (13) in a moderate yield (Scheme 2). Alkylation of thioester 13 with the δ-iodo derivative of protected (S)-norvaline ( 14) smoothly led to (nido-carboran-9-yl)-5-methylthionorvaline derivative 15 as a zwitterion.…”

“…s, B10), −37.3 (d, 1B, J = 143.8 Hz, B1). 13 C{ 1 H} NMR (DMSO-d 6 , 126 MHz) (diastereomers I and II): δ 168.0 (C-1, II), 167.8 (C-1, I), 156.7 (q, J = 37.4 Hz, NCO, (I)), 156.5 (q, J = 37.4 Hz, NCO, (II), 115.5 (q, J = 287.9 Hz, CF 3 (I and II)), 53.11 (OMe, II), 53.07 (OMe, I), 49.5 (C-2, II), 48.7 (C-2, I), 44.9 (br s, CH-carborane, I), 44.5 (br s, CH-carborane, II), 42.0 (C-3, II), 41.9 (C-3, I), 23.9 (SMe, II), 22.6 (SMe,I) ,28.63;H,5.61;N,3.71;S,8.49. Found: C,28.64;H,5.34;N,3.79;S,8.25.…”

“…The diastereomers of compounds 10 and 11 were distinguished by chiral HPLC and 1 H, 19 F, and 13 C NMR spectroscopy. In the case of compound 11b, the assignment of signals in the 1 H and 13 C NMR spectra was made based on 2D NMR experiments (Figure 3).…”

“…The residue was treated with a n-hexane−EtOAc mixture 1:1 (20 mL). The precipitate was filtered and washed with Et 13 C{ 1 H} NMR (DMSO-d 6 , 126 MHz) (diastereomers I and II): δ 170.6 (COOH), 157.9 (q, J = 30.8 Hz, COO), 117.2 (q, J = 300.6 Hz, CF 3 ), 51.7 (br s, C-2), 50.8 (br s, CH-carborane), 43.2 and 41.0 (C-5), 37.6 (CHcarborane), 28.7 (br s, C-3), 21.3 and 21.1 (SMe). HRMS (ESI) m/z: [M − CF 3 CO 2 H] − calcd for C 8 H 23 11 B 9 NO 2 S 296.2308; found 296.2304.…”

“Free of Base” Sulfa-Michael Addition for Novel o-Carboranyl-DL-Cysteine Synthesis

“…In this regard, the chemistry of dicarbaboranes [C 2 B 10 H 12 ] and their derivatives has been well investigated [16]. The synthesis of o-carboranes containing unnatural ω-mercapto-amino L-o-carboranyl-alanine 2 [18] as well as o-carboranyl derivatives of (S)-Asparagine 3a and (S)-Glutamine 3b [19], phenylalanine 4 [20] and (S)-m-carboranyl-homocysteine sulfoxide 5 [21], have been published. Our current interest was inspired by the recent synthesis [22] of m-carboranyl-cysteine 6 and its biological evaluation as an agent for Boron Neutron Capture Therapy [23,24] (Figure 1).…”